Optional源码解析与实践

1 导读

NullPointerException在开发过程中经常遇到，稍有不慎小BUG就出现了，如果避免这个问题呢，Optional就是专门解决这个问题的类，那么Optional如何使用呢？让我们一起探索一下吧！

2 源码解析

2.1 Optional定义

Optional类是Java8为了解决null值判断问题而创建的容器类，在java.util 下,使用Optional类可以避免显式的null值判断，避免null导致的NullPointerException。首先，Optional是一个容器，它可以保存类型T的值，也可以为null的容器对象。Optional容器只能存一个值。

2.2 Optional的属性

1）源码：
  1. <span class="com">/**</span>
  2. <span class="com">* Common instance for {@code empty()}.</span>
  3. <span class="com">*/</span>
  4. <span class="kwd">private <span class="pln"> <span class="kwd">static <span class="pln"> <span class="kwd">final <span class="pln"> <span class="typ">Optional <span class="pun">&lt;?&gt; <span class="pln">EMPTY  <span class="pun">= <span class="pln"> <span class="kwd">new <span class="pln"> <span class="typ">Optional <span class="pun">&lt;&gt;();</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  7. <span class="com">/**</span>
  8. <span class="com">* If non-null, the value; if null, indicates no value is present</span>
  9. <span class="com">*/</span>
  10. <span class="kwd">private <span class="pln"> <span class="kwd">final <span class="pln">T value <span class="pun">;</span> </span> </span> </span> </span>

根据源码可以看到Optional有两个属性，一个是为空值准备的EMPTY和泛型值value;

2.3 Optional的方法

Optional除toString()、hashCode() 、equals()等Object的方法外，还包含以下方法。

2.3.1 私有构造方法
  1. <span class="com">/**</span>
  2. <span class="com">* Constructs an empty instance.</span>
  3. <span class="com">*</span>
  4. <span class="com">* @implNote Generally only one empty instance, {@link Optional#EMPTY},</span>
  5. <span class="com">* should exist per VM.</span>
  6. <span class="com">*/</span>
  7. <span class="kwd">private <span class="pln"> <span class="typ">Optional <span class="pun">() <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span>
  8. <span class="pln"> <span class="kwd">this <span class="pun">. <span class="pln">value  <span class="pun">= <span class="pln"> <span class="kwd">null <span class="pun">;</span> </span> </span> </span> </span> </span> </span> </span>
  9. <span class="pun">}</span>
  12. <span class="com">/**</span>
  13. <span class="com">* Constructs an instance with the value present.</span>
  14. <span class="com">*</span>
  15. <span class="com">* @param value the non-null value to be present</span>
  16. <span class="com">* @throws NullPointerException if value is null</span>
  17. <span class="com">*/</span>
  18. <span class="kwd">private <span class="pln"> <span class="typ">Optional <span class="pun">( <span class="pln">T value <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span>
  19. <span class="pln"> <span class="kwd">this <span class="pun">. <span class="pln">value  <span class="pun">= <span class="pln"> <span class="typ">Objects <span class="pun">. <span class="pln">requireNonNull <span class="pun">( <span class="pln">value <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  20. <span class="pun">}</span>

分别是创建一个空实例和构造一个具有当前值的实例。

2.3.2 创建方法
1）源码
  1. <span class="kwd">public <span class="pln"> <span class="kwd">static <span class="pun">&lt; <span class="pln">T <span class="pun">&gt; <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="pln">T <span class="pun">&gt; <span class="pln">empty <span class="pun">() <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  2. <span class="pln"> <span class="lit">@SuppressWarnings <span class="pun">( <span class="str">"unchecked" <span class="pun">)</span> </span> </span> </span> </span>
  3. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="pln">T <span class="pun">&gt; <span class="pln">t  <span class="pun">= <span class="pln"> <span class="pun">( <span class="typ">Optional <span class="pun">&lt; <span class="pln">T <span class="pun">&gt;) <span class="pln">EMPTY <span class="pun">;</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  4. <span class="pln"> <span class="kwd">return <span class="pln">t <span class="pun">;</span> </span> </span> </span>
  5. <span class="pun">}</span>
  6. <span class="kwd">public <span class="pln"> <span class="kwd">static <span class="pln"> <span class="pun">&lt; <span class="pln">T <span class="pun">&gt; <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="pln">T <span class="pun">&gt; <span class="pln">of <span class="pun">( <span class="pln">T value <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  7. <span class="pln"> <span class="kwd">return <span class="pln"> <span class="kwd">new <span class="pln"> <span class="typ">Optional <span class="pun">&lt;&gt;( <span class="pln">value <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  8. <span class="pun">}</span>
  9. <span class="kwd">public <span class="pln"> <span class="kwd">static <span class="pln"> <span class="pun">&lt; <span class="pln">T <span class="pun">&gt; <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="pln">T <span class="pun">&gt; <span class="pln">ofNullable <span class="pun">( <span class="pln">T value <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  10. <span class="pln"> <span class="kwd">return <span class="pln">value  <span class="pun">== <span class="pln"> <span class="kwd">null <span class="pln"> <span class="pun">? <span class="pln">empty <span class="pun">() <span class="pln"> <span class="pun">: <span class="pln">of <span class="pun">( <span class="pln">value <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  11. <span class="pun">}</span>
2）方法说明
  • empty(）: 创建一个空的 Optional 实例
  • of(T t) : 创建一个 Optional 实例，当 t为null时抛出异常
  • ofNullable(T t): 创建一个 Optional 实例，但当 t为null时不会抛出异常，而是返回一个空的实例

3）测试代码

  1. <span class="kwd">public <span class="pln"> <span class="kwd">static <span class="pln"> <span class="kwd">void <span class="pln">main <span class="pun">( <span class="typ">String <span class="pun">[] <span class="pln">args <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  2. <span class="pln"> <span class="typ">Integer <span class="pln">value1  <span class="pun">= <span class="pln"> <span class="kwd">null <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  3. <span class="pln"> <span class="typ">Integer <span class="pln">value2  <span class="pun">= <span class="pln"> <span class="lit">1 <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  4. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  5. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional1  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">empty <span class="pun">();</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  6. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1创建了" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  7. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  8. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1失败了" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  9. <span class="pln"> <span class="pun">}</span> </span>
  10. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  11. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional2  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">of <span class="pun">( <span class="pln">value1 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  12. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2创建了" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  13. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  14. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2失败了" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  15. <span class="pln"> <span class="pun">}</span> </span>
  16. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  17. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional3  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">ofNullable <span class="pun">( <span class="pln">value1 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  18. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional3创建了" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  19. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  20. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional3失败了" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  21. <span class="pln"> <span class="pun">}</span> </span>
  22. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  23. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional4  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">of <span class="pun">( <span class="pln">value2 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  24. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional4创建了" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  25. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  26. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional4失败了" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  27. <span class="pln"> <span class="pun">}</span> </span>
  28. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  29. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional5  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">ofNullable <span class="pun">( <span class="pln">value2 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  30. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional5创建了" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  31. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  32. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional5失败了" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  33. <span class="pln"> <span class="pun">}</span> </span>
  34. <span class="pun">}</span>

4）运行结果

2.3.3 值获取方法
1）源码
  1. <span class="kwd">public <span class="pln">T get <span class="pun">() <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span>
  2. <span class="pln"> <span class="kwd">if <span class="pln"> <span class="pun">( <span class="pln">value  <span class="pun">== <span class="pln"> <span class="kwd">null <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  3. <span class="pln"> <span class="kwd">throw <span class="pln"> <span class="kwd">new <span class="pln"> <span class="typ">NoSuchElementException <span class="pun">( <span class="str">"No value present" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  4. <span class="pln"> <span class="pun">}</span> </span>
  5. <span class="pln"> <span class="kwd">return <span class="pln">value <span class="pun">;</span> </span> </span> </span>
  6. <span class="pun">}</span>
2）方法说明

get(): 如果Optional不为空，则返回该Optional容器中的值，否则抛出NoSuchElementExceptio 。

3）测试代码
  1. <span class="kwd">public <span class="pln"> <span class="kwd">static <span class="pln"> <span class="kwd">void <span class="pln">main <span class="pun">( <span class="typ">String <span class="pun">[] <span class="pln">args <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  2. <span class="pln"> <span class="typ">Integer <span class="pln">value1  <span class="pun">= <span class="pln"> <span class="kwd">null <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  3. <span class="pln"> <span class="typ">Integer <span class="pln">value2  <span class="pun">= <span class="pln"> <span class="lit">1 <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  4. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional1  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">ofNullable <span class="pun">( <span class="pln">value1 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  5. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional2  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">of <span class="pun">( <span class="pln">value2 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  6. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  7. <span class="pln"> <span class="typ">Integer <span class="pln">result <span class="pun">= <span class="pln">optional1 <span class="pun">. <span class="pln">get <span class="pun">();</span> </span> </span> </span> </span> </span> </span> </span>
  8. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的值是：" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  9. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  10. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的值获取失败,原因:" <span class="pun">+ <span class="pln">e <span class="pun">. <span class="pln">getMessage <span class="pun">());</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  11. <span class="pln"> <span class="pun">}</span> </span>
  12. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  13. <span class="pln"> <span class="typ">Integer <span class="pln">result <span class="pun">= <span class="pln">optional2 <span class="pun">. <span class="pln">get <span class="pun">();</span> </span> </span> </span> </span> </span> </span> </span>
  14. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2的值是：" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  15. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  16. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2的值获取失败,原因:" <span class="pun">+ <span class="pln">e <span class="pun">. <span class="pln">getMessage <span class="pun">());</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  17. <span class="pln"> <span class="pun">}</span> </span>
  18. <span class="pun">}</span>
4）运行结果

2.3.4 判断方法
1）源码
  1. <span class="kwd">public <span class="pln"> <span class="kwd">boolean <span class="pln">isPresent <span class="pun">() <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span>
  2. <span class="pln"> <span class="kwd">return <span class="pln">value  <span class="pun">!= <span class="pln"> <span class="kwd">null <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  3. <span class="pun">}</span>
  4. <span class="kwd">public <span class="pln"> <span class="kwd">void <span class="pln">ifPresent <span class="pun">( <span class="typ">Consumer <span class="pun">&lt;? <span class="pln"> <span class="kwd">super <span class="pln">T <span class="pun">&gt; <span class="pln">consumer <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  5. <span class="pln"> <span class="kwd">if <span class="pln"> <span class="pun">( <span class="pln">value  <span class="pun">!= <span class="pln"> <span class="kwd">null <span class="pun">)</span> </span> </span> </span> </span> </span> </span> </span> </span>
  6. <span class="pln">consumer <span class="pun">. <span class="pln">accept <span class="pun">( <span class="pln">value <span class="pun">);</span> </span> </span> </span> </span> </span>
  7. <span class="pun">}</span>
  8. <span class="kwd">public <span class="pln">T orElse <span class="pun">( <span class="pln">T other <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span>
  9. <span class="pln"> <span class="kwd">return <span class="pln">value  <span class="pun">!= <span class="pln"> <span class="kwd">null <span class="pln"> <span class="pun">? <span class="pln">value  <span class="pun">: <span class="pln">other <span class="pun">;</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  10. <span class="pln"> <span class="pun">}</span> </span>
  11. <span class="kwd">public <span class="pln">T orElseGet <span class="pun">( <span class="typ">Supplier <span class="pun">&lt;? <span class="pln"> <span class="kwd">extends <span class="pln">T <span class="pun">&gt; <span class="pln">other <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  12. <span class="pln"> <span class="kwd">return <span class="pln">value  <span class="pun">!= <span class="pln"> <span class="kwd">null <span class="pln"> <span class="pun">? <span class="pln">value  <span class="pun">: <span class="pln">other <span class="pun">. <span class="pln">get <span class="pun">();</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  13. <span class="pun">}</span>
  14. <span class="kwd">public <span class="pln"> <span class="pun">&lt; <span class="pln">X  <span class="kwd">extends <span class="pln"> <span class="typ">Throwable <span class="pun">&gt; <span class="pln">T orElseThrow <span class="pun">( <span class="typ">Supplier <span class="pun">&lt;? <span class="pln"> <span class="kwd">extends <span class="pln">X <span class="pun">&gt; <span class="pln">exceptionSupplier <span class="pun">) <span class="pln"> <span class="kwd">throws <span class="pln">X  <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  15. <span class="pln"> <span class="kwd">if <span class="pln"> <span class="pun">( <span class="pln">value  <span class="pun">!= <span class="pln"> <span class="kwd">null <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  16. <span class="pln"> <span class="kwd">return <span class="pln">value <span class="pun">;</span> </span> </span> </span>
  17. <span class="pln"> <span class="pun">} <span class="pln"> <span class="kwd">else <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span>
  18. <span class="pln"> <span class="kwd">throw <span class="pln">exceptionSupplier <span class="pun">. <span class="pln">get <span class="pun">();</span> </span> </span> </span> </span> </span>
  19. <span class="pln"> <span class="pun">}</span> </span>
  20. <span class="pun">}</span>
2）方法说明
  • isPresent(): 判断optional是否为空，如果空则返回false，否则返回true
  • ifPresent(Consumer c): 如果optional不为空，则将optional中的对象传给Comsumer函数
  • orElse(T other): 如果optional不为空，则返回optional中的对象；如果为null，则返回 other 这个对象。
  • orElseGet(Supplier other): 如果optional不为空，则返回optional中的对象；如果为null，否则调用其他函数并返回调用的结果
  • orElseThrow(Supplier exception): 如果optional不为空，则返回optional中的对象；如果为null，则抛出Supplier函数生成的异常
3）测试代码
  1. <span class="kwd">public <span class="pln"> <span class="kwd">static <span class="pln"> <span class="kwd">void <span class="pln">main <span class="pun">( <span class="typ">String <span class="pun">[] <span class="pln">args <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  2. <span class="pln"> <span class="typ">Integer <span class="pln">value1  <span class="pun">= <span class="pln"> <span class="kwd">null <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  3. <span class="pln"> <span class="typ">Integer <span class="pln">value2  <span class="pun">= <span class="pln"> <span class="lit">1 <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  4. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional1  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">ofNullable <span class="pun">( <span class="pln">value1 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  5. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional2  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">of <span class="pun">( <span class="pln">value2 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  6. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  7. <span class="pln"> <span class="kwd">if <span class="pun">( <span class="pln">optional1 <span class="pun">. <span class="pln">isPresent <span class="pun">()){</span> </span> </span> </span> </span> </span> </span>
  8. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的isPresent结果不为空" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  9. <span class="pln"> <span class="pun">} <span class="kwd">else <span class="pun">{</span> </span> </span> </span>
  10. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的isPresent结果为空" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  11. <span class="pln"> <span class="pun">}</span> </span>
  12. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  13. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的isPresent判空失败,原因:" <span class="pun">+ <span class="pln">e <span class="pun">. <span class="pln">getMessage <span class="pun">());</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  14. <span class="pln"> <span class="pun">}</span> </span>
  15. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  16. <span class="pln"> <span class="kwd">if <span class="pun">( <span class="pln">optional2 <span class="pun">. <span class="pln">isPresent <span class="pun">()){</span> </span> </span> </span> </span> </span> </span>
  17. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2的isPresent结果不为空" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  18. <span class="pln"> <span class="pun">} <span class="kwd">else <span class="pun">{</span> </span> </span> </span>
  19. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2的isPresent结果为空" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  20. <span class="pln"> <span class="pun">}</span> </span>
  21. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  22. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2的isPresent判空失败,原因:" <span class="pun">+ <span class="pln">e <span class="pun">. <span class="pln">getMessage <span class="pun">());</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  23. <span class="pln"> <span class="pun">}</span> </span>
  26. <span class="pln">optional1 <span class="pun">. <span class="pln">ifPresent <span class="pun">( <span class="pln">t <span class="pun">-&gt;{</span> </span> </span> </span> </span> </span>
  27. <span class="pln"> <span class="kwd">int <span class="pln">i  <span class="pun">= <span class="pln">t <span class="pun">+ <span class="lit">1 <span class="pun">;</span> </span> </span> </span> </span> </span> </span> </span>
  28. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1处理后的值是" <span class="pun">+ <span class="pln">i <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  29. <span class="pln"> <span class="pun">});</span> </span>
  30. <span class="pln">optional2 <span class="pun">. <span class="pln">ifPresent <span class="pun">( <span class="pln">t <span class="pun">-&gt;{</span> </span> </span> </span> </span> </span>
  31. <span class="pln"> <span class="kwd">int <span class="pln">i  <span class="pun">= <span class="pln">t <span class="pun">+ <span class="lit">1 <span class="pun">;</span> </span> </span> </span> </span> </span> </span> </span>
  32. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2处理后的值是" <span class="pun">+ <span class="pln">i <span class="pun">);});</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  35. <span class="pln"> <span class="typ">Integer <span class="pln">value3  <span class="pun">= <span class="pln"> <span class="lit">2 <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  36. <span class="pln"> <span class="typ">Integer <span class="pln">result  <span class="pun">= <span class="pln">optional1 <span class="pun">. <span class="pln">orElse <span class="pun">( <span class="pln">value3 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  37. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1执行orElse处理后的值是" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  40. <span class="pln">result  <span class="pun">= <span class="pln">optional2 <span class="pun">. <span class="pln">orElse <span class="pun">( <span class="pln">value3 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span>
  41. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2执行orElse处理后的值是" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  44. <span class="pln">result  <span class="pun">= <span class="pln">optional1 <span class="pun">. <span class="pln">orElseGet <span class="pun">(()-&gt; <span class="pln"> <span class="kwd">new <span class="pln"> <span class="typ">Integer <span class="pun">(- <span class="lit">1 <span class="pun">));</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  45. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1执行orElseGet处理后的值是" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  48. <span class="pln">result  <span class="pun">= <span class="pln">optional2 <span class="pun">. <span class="pln">orElseGet <span class="pun">(()-&gt; <span class="pln"> <span class="kwd">new <span class="pln"> <span class="typ">Integer <span class="pun">(- <span class="lit">1 <span class="pun">));</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  49. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2执行orElseGet处理后的值是" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  50. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  51. <span class="pln">result  <span class="pun">= <span class="pln">optional1 <span class="pun">. <span class="pln">orElseThrow  <span class="pun">(()-&gt; <span class="pln"> <span class="kwd">new <span class="pln"> <span class="typ">RuntimeException <span class="pun">( <span class="str">"值是空的" <span class="pun">));</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  52. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1执行orElseThrow处理后的值是" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  53. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  54. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的orElseThrow抛出异常:" <span class="pun">+ <span class="pln">e <span class="pun">. <span class="pln">getMessage <span class="pun">());</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  55. <span class="pln"> <span class="pun">}</span> </span>
  56. <span class="pln"> <span class="kwd">try <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  57. <span class="pln">result  <span class="pun">= <span class="pln">optional2 <span class="pun">. <span class="pln">orElseThrow  <span class="pun">(()-&gt; <span class="pln"> <span class="kwd">new <span class="pln"> <span class="typ">RuntimeException <span class="pun">( <span class="str">"值是空的" <span class="pun">));</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  58. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2执行orElseThrow处理后的值是" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  59. <span class="pln"> <span class="pun">} <span class="kwd">catch <span class="pln"> <span class="pun">( <span class="typ">Exception <span class="pln">e <span class="pun">){</span> </span> </span> </span> </span> </span> </span> </span>
  60. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2的orElseThrow抛出异常:" <span class="pun">+ <span class="pln">e <span class="pun">. <span class="pln">getMessage <span class="pun">());</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
4）运行结果

2.3.5 过滤方法
1）源码
  1. <span class="kwd">public <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="pln">T <span class="pun">&gt; <span class="pln">filter <span class="pun">( <span class="typ">Predicate <span class="pun">&lt;? <span class="pln"> <span class="kwd">super <span class="pln">T <span class="pun">&gt; <span class="pln">predicate <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  2. <span class="pln"> <span class="typ">Objects <span class="pun">. <span class="pln">requireNonNull <span class="pun">( <span class="pln">predicate <span class="pun">);</span> </span> </span> </span> </span> </span> </span>
  3. <span class="pln"> <span class="kwd">if <span class="pln"> <span class="pun">(! <span class="pln">isPresent <span class="pun">())</span> </span> </span> </span> </span> </span>
  4. <span class="pln"> <span class="kwd">return <span class="pln"> <span class="kwd">this <span class="pun">;</span> </span> </span> </span> </span>
  5. <span class="pln"> <span class="kwd">else</span> </span>
  6. <span class="pln"> <span class="kwd">return <span class="pln">predicate <span class="pun">. <span class="pln">test <span class="pun">( <span class="pln">value <span class="pun">) <span class="pln"> <span class="pun">? <span class="pln"> <span class="kwd">this <span class="pln"> <span class="pun">: <span class="pln">empty <span class="pun">();</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  7. <span class="pun">}</span>
2）方法说明

filter(Predicate p): 如果optional不为空，则执行Predicate p，如果p的结果为true，则返回原本的optional，否则返回空的optional

3）测试代码
  1. <span class="kwd">public <span class="pln"> <span class="kwd">static <span class="pln"> <span class="kwd">void <span class="pln">main <span class="pun">( <span class="typ">String <span class="pun">[] <span class="pln">args <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  2. <span class="pln"> <span class="typ">Integer <span class="pln">value1  <span class="pun">= <span class="pln"> <span class="lit">5 <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  3. <span class="pln"> <span class="typ">Integer <span class="pln">value2  <span class="pun">= <span class="pln"> <span class="lit">6 <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  4. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional1  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">ofNullable <span class="pun">( <span class="pln">value1 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  5. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">optional2  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">of <span class="pun">( <span class="pln">value2 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  8. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">result  <span class="pun">= <span class="pln">optional1 <span class="pun">. <span class="pln">filter <span class="pun">( <span class="pln">t <span class="pun">-&gt; <span class="pln">t  <span class="pun">&gt; <span class="pln"> <span class="lit">5 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  9. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的filter后的值:" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  10. <span class="pln">result  <span class="pun">= <span class="pln">optional2 <span class="pun">. <span class="pln">filter <span class="pun">( <span class="pln">t <span class="pun">-&gt; <span class="pln">t  <span class="pun">&gt; <span class="pln"> <span class="lit">5 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  11. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2的filter后的值:" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
4）运行结果

2.3.6 映射方法
1）源码
  1. <span class="kwd">public <span class="pun">&lt; <span class="pln">U <span class="pun">&gt; <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="pln">U <span class="pun">&gt; <span class="pln">map <span class="pun">( <span class="typ">Function <span class="pun">&lt;? <span class="pln"> <span class="kwd">super <span class="pln">T <span class="pun">, <span class="pln"> <span class="pun">? <span class="pln"> <span class="kwd">extends <span class="pln">U <span class="pun">&gt; <span class="pln">mapper <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  2. <span class="pln"> <span class="typ">Objects <span class="pun">. <span class="pln">requireNonNull <span class="pun">( <span class="pln">mapper <span class="pun">);</span> </span> </span> </span> </span> </span> </span>
  3. <span class="pln"> <span class="kwd">if <span class="pln"> <span class="pun">(! <span class="pln">isPresent <span class="pun">())</span> </span> </span> </span> </span> </span>
  4. <span class="pln"> <span class="kwd">return <span class="pln">empty <span class="pun">();</span> </span> </span> </span>
  5. <span class="pln"> <span class="kwd">else <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  6. <span class="pln"> <span class="kwd">return <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">ofNullable <span class="pun">( <span class="pln">mapper <span class="pun">. <span class="pln">apply <span class="pun">( <span class="pln">value <span class="pun">));</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  7. <span class="pln"> <span class="pun">}</span> </span>
  8. <span class="pun">}</span>
  9. <span class="kwd">public <span class="pun">&lt; <span class="pln">U <span class="pun">&gt; <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="pln">U <span class="pun">&gt; <span class="pln">flatMap <span class="pun">( <span class="typ">Function <span class="pun">&lt;? <span class="pln"> <span class="kwd">super <span class="pln">T <span class="pun">, <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="pln">U <span class="pun">&gt;&gt; <span class="pln">mapper <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  10. <span class="pln"> <span class="typ">Objects <span class="pun">. <span class="pln">requireNonNull <span class="pun">( <span class="pln">mapper <span class="pun">);</span> </span> </span> </span> </span> </span> </span>
  11. <span class="pln"> <span class="kwd">if <span class="pln"> <span class="pun">(! <span class="pln">isPresent <span class="pun">())</span> </span> </span> </span> </span> </span>
  12. <span class="pln"> <span class="kwd">return <span class="pln">empty <span class="pun">();</span> </span> </span> </span>
  13. <span class="pln"> <span class="kwd">else <span class="pln"> <span class="pun">{</span> </span> </span> </span>
  14. <span class="pln"> <span class="kwd">return <span class="pln"> <span class="typ">Objects <span class="pun">. <span class="pln">requireNonNull <span class="pun">( <span class="pln">mapper <span class="pun">. <span class="pln">apply <span class="pun">( <span class="pln">value <span class="pun">));</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  15. <span class="pln"> <span class="pun">}</span> </span>
  16. <span class="pun">}</span>
2）方法说明
  • map(Function<t, u=""> mapper): 如果存在一个值，则对其应用提供的映射函数，如果结果非空，则返回描述结果的Optional。 否则返回一个空的Optional。
  • flatMap(Function< T,Optional> mapper): 如果有值，则对其应用提供的可选映射函数，返回结果，否则返回空的可选函数。 这个方法类似于map(Function)，但是提供的映射器的结果已经是一个可选的，如果调用，flatMap不会用额外的可选的包装它。
  • 区别：map会自动将u放到optional中，而flatMap则需要手动给u创建一个optional
3）测试代码

  1. <span class="pln"> <span class="kwd">public <span class="pln"> <span class="kwd">static <span class="pln"> <span class="kwd">void <span class="pln">main <span class="pun">( <span class="typ">String <span class="pun">[] <span class="pln">args <span class="pun">) <span class="pln"> <span class="pun">{</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  2. <span class="pln"> <span class="typ">User <span class="pln">user1  <span class="pun">= <span class="pln"> <span class="kwd">null <span class="pun">;</span> </span> </span> </span> </span> </span> </span>
  3. <span class="pln"> <span class="typ">User <span class="pln">user2  <span class="pun">= <span class="pln"> <span class="kwd">new <span class="pln"> <span class="typ">User <span class="pun">( <span class="str">"user2名字" <span class="pun">, <span class="lit">19 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  4. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">User <span class="pun">&gt; <span class="pln">optional1  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">ofNullable <span class="pun">( <span class="pln">user1 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  5. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">User <span class="pun">&gt; <span class="pln">optional2  <span class="pun">= <span class="pln"> <span class="typ">Optional <span class="pun">. <span class="pln">of <span class="pun">( <span class="pln">user2 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  6. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"=========map==========" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  7. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的map前的值:" <span class="pun">+ <span class="pln">optional1 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  8. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">String <span class="pun">&gt; <span class="pln">result  <span class="pun">= <span class="pln">optional1 <span class="pun">. <span class="pln">map <span class="pun">( <span class="pln">t <span class="pun">-&gt; <span class="pln">t <span class="pun">. <span class="pln">getName <span class="pun">());</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  9. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的map后的值:" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  12. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2的map前的值:" <span class="pun">+ <span class="pln">optional2 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  13. <span class="pln">result  <span class="pun">= <span class="pln">optional2 <span class="pun">. <span class="pln">map <span class="pun">( <span class="pln">t <span class="pun">-&gt; <span class="pln">t <span class="pun">. <span class="pln">getName <span class="pun">());</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  14. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional2的map后的值:" <span class="pun">+ <span class="pln">result <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  17. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"===========flatMap========" <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span>
  20. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的flatMap前的值:" <span class="pun">+ <span class="pln">optional1 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  21. <span class="pln"> <span class="typ">Optional <span class="pun">&lt; <span class="typ">Integer <span class="pun">&gt; <span class="pln">result2  <span class="pun">= <span class="pln">optional1 <span class="pun">. <span class="pln">flatMap <span class="pun">( <span class="pln">t <span class="pun">-&gt; <span class="typ">Optional <span class="pun">. <span class="pln">ofNullable <span class="pun">( <span class="pln">t <span class="pun">. <span class="pln">getAge <span class="pun">()));</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>
  22. <span class="pln"> <span class="typ">System <span class="pun">. <span class="pln">out <span class="pun">. <span class="pln">println <span class="pun">( <span class="str">"optional1的flatMap后的值:" <span class="pun">+ <span class="pln">result2 <span class="pun">);</span> </span> </span> </span> </span> </span> </span> </span> </span> </span> </span>

标签: Javascript

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