《Java8实战》汇总

参考书籍：《Java8 实战》

一、Lambda表达式

   Lambda 是一个匿名函数。可以写出更简洁、更灵活的代码。作为一种更紧凑的代码风格，使Java的语言表达能力得到了提升。

1.1、Lambda表达式的关键：从匿名类到 Lambda 的转换

示例：

<span style="background-color:#f8f8f8"><span style="color:#333333">  <span style="color:#000000">public</span> <span style="color:#000000">static</span> <span style="color:#000000">void</span> <span style="color:#000000">main</span>(<span style="color:#000000">String</span>[] <span style="color:#000000">args</span>) {           <span style="color:#aa5500">//创建线程--匿名类写法</span>           <span style="color:#000000">Thread</span> <span style="color:#000000">td</span> <span style="color:#981a1a">=</span> <span style="color:#221199">new</span> <span style="color:#000000">Thread</span>(<span style="color:#221199">new</span> <span style="color:#000000">Runnable</span>() {               <span style="color:#000000">@Override</span>               <span style="color:#000000">public</span> <span style="color:#000000">void</span> <span style="color:#000000">run</span>() {                   <span style="color:#000000">System</span><span style="color:#116644">.</span><span style="color:#000000">out</span><span style="color:#116644">.</span><span style="color:#221199">println</span>(<span style="color:#aa1111">"hello,Lamada!"</span>);               }           });           <span style="color:#000000">td</span><span style="color:#116644">.</span><span style="color:#000000">start</span>();                      <span style="color:#aa5500">//lamada写法--面向函数式编程(匿名函数)</span>           <span style="color:#000000">Thread</span> <span style="color:#000000">td1</span> <span style="color:#981a1a">=</span> <span style="color:#221199">new</span> <span style="color:#000000">Thread</span>(() <span style="color:#981a1a">-></span> <span style="color:#000000">System</span><span style="color:#116644">.</span><span style="color:#000000">out</span><span style="color:#116644">.</span><span style="color:#221199">println</span>(<span style="color:#aa1111">"hello,Lamada01!"</span>));           <span style="color:#000000">td1</span><span style="color:#116644">.</span><span style="color:#000000">start</span>();       }</span></span>

1.2、Lambda表达式语法

   Lambda表达式在Java 语言中引入了一个新的语法元素和操作符。这个操作符为 “->” ， 该操作符被称 为 Lambda 操作符或箭头操作符。它将 Lambda 分为两个部分：

• 左侧： 指定了 Lambda 表达式需要的所有参数

• 右侧： 指定了 Lambda 体，即 Lambda 表达式要执行的功能。

（1）语法格式一：无参，无返回值，Lambda 体只需一条语句    示例：Runnable r1 = () -> System.out.println("Hello Lambda!"); （2）语法格式二：Lambda 需要一个参数    示例：Consumer<String> con = （x） -> System.out.println(x); （3）语法格式三：Lambda 只需要一个参数时，参数的小括号可以省略    示例：Consumer<String> con = x -> System.out.println(x); （4）语法格式四：Lambda 需要两个参数，并且有返回值    示例：

<span style="background-color:#f8f8f8"><span style="color:#333333"><span style="color:#000000">Comparator</span><span style="color:#981a1a"><</span><span style="color:#000000">Integer</span><span style="color:#981a1a">></span> <span style="color:#000000">com</span> <span style="color:#981a1a">=</span> (<span style="color:#000000">x</span>, <span style="color:#000000">y</span>) <span style="color:#981a1a">-></span> {   <span style="color:#000000">System</span><span style="color:#116644">.</span><span style="color:#000000">out</span><span style="color:#116644">.</span><span style="color:#221199">println</span>(<span style="color:#aa1111">"函数式接口"</span>);    <span style="color:#770088">return</span> <span style="color:#000000">Integer</span><span style="color:#116644">.</span><span style="color:#000000">compare</span>(<span style="color:#000000">x</span>, <span style="color:#000000">y</span>);};</span></span>

（5）语法格式五：当 Lambda 体只有一条语句时，return 与大括号可以省略    示例：Comparator<Integer> com = (x, y) -> Integer.compare(x, y); （6）Lambda 表达式的参数列表的数据类型可以省略不写，因为JVM编译器通过上下文推断出，数据类型，即“类型推断”    示例：

<span style="background-color:#f8f8f8"><span style="color:#333333"><span style="color:#000000">Comparator</span><span style="color:#981a1a"><</span><span style="color:#000000">Integer</span><span style="color:#981a1a">></span> <span style="color:#000000">com</span> <span style="color:#981a1a">=</span> (<span style="color:#000000">Integer</span> <span style="color:#000000">x</span>,<span style="color:#000000">Integer</span> <span style="color:#000000">y</span>) <span style="color:#981a1a">-></span> {  <span style="color:#aa5500">//Integer 类型可以省略</span>  <span style="color:#000000">System</span><span style="color:#116644">.</span><span style="color:#000000">out</span><span style="color:#116644">.</span><span style="color:#221199">println</span>(<span style="color:#aa1111">"函数式接口"</span>);  <span style="color:#770088">return</span> <span style="color:#000000">Integer</span><span style="color:#116644">.</span><span style="color:#000000">compare</span>(<span style="color:#000000">x</span>, <span style="color:#000000">y</span>);
};</span></span>

  类型推断：Lambda 表达式中的参数类型都是由编译器推断得出的（Lambda 表达式的类型依赖于上下文环境，是由编译器推断出来的）。

二、函数式接口

2.1、什么是函数式接口

（1）只包含一个抽象方法的接口，称为函数式接口。 （2）你可以通过 Lambda 表达式来创建该接口的对象。（若 Lambda 表达式抛出一个受检异常，那么该异常需要在目标接口的抽象方法上进行声明）。 （3）我们可以在任意函数式接口上使用 @FunctionalInterface 注解， 这样做可以检查它是否是一个函数式接口，同时 javadoc 也会包含一条声明，说明这个接口是一个函数式接口。

   作为参数传递 Lambda 表达式：为了将 Lambda 表达式作为参数传递，接收Lambda 表达式的参数类型必须是与该 Lambda 表达式兼容的函数式接口的类型。

2.2、Java 内置四大核心函数式接口

<span style="background-color:#f8f8f8"><span style="color:#333333">   <span style="color:#000000">class</span> <span style="color:#000000">TestConsumer</span> <span style="color:#000000">implements</span> <span style="color:#000000">Consumer</span><span style="color:#981a1a"><</span><span style="color:#000000">String</span><span style="color:#981a1a">></span> {       <span style="color:#000000">@Override</span>       <span style="color:#000000">public</span> <span style="color:#000000">void</span> <span style="color:#000000">accept</span>(<span style="color:#000000">String</span> <span style="color:#000000">t</span>) {           <span style="color:#000000">System</span><span style="color:#116644">.</span><span style="color:#000000">out</span><span style="color:#116644">.</span><span style="color:#221199">println</span>(<span style="color:#aa1111">"消费型接口。。。"</span>);       }   }      <span style="color:#000000">class</span> <span style="color:#000000">TestSupplier</span> <span style="color:#000000">implements</span> <span style="color:#000000">Supplier</span><span style="color:#981a1a"><</span><span style="color:#000000">String</span><span style="color:#981a1a">></span> {       <span style="color:#000000">@Override</span>       <span style="color:#000000">public</span> <span style="color:#000000">String</span> <span style="color:#000000">get</span>() {           <span style="color:#770088">return</span> <span style="color:#221199">new</span> <span style="color:#000000">String</span>();       }   }      <span style="color:#000000">class</span> <span style="color:#000000">TestFunction</span> <span style="color:#000000">implements</span> <span style="color:#000000">Function</span><span style="color:#981a1a"><</span><span style="color:#000000">Integer</span>, <span style="color:#000000">String</span><span style="color:#981a1a">></span> {       <span style="color:#000000">@Override</span>       <span style="color:#000000">public</span> <span style="color:#000000">String</span> <span style="color:#000000">apply</span>(<span style="color:#000000">Integer</span> <span style="color:#000000">t</span>) {           <span style="color:#770088">return</span> <span style="color:#221199">new</span> <span style="color:#000000">String</span>();       }   }   <span style="color:#000000">class</span> <span style="color:#000000">TestPredicate</span> <span style="color:#000000">implements</span> <span style="color:#000000">Predicate</span><span style="color:#981a1a"><</span><span style="color:#000000">String</span><span style="color:#981a1a">></span> {       <span style="color:#000000">@Override</span>       <span style="color:#000000">public</span> <span style="color:#000000">boolean</span> <span style="color:#000000">test</span>(<span style="color:#000000">String</span> <span style="color:#000000">t</span>) {           <span style="color:#770088">return</span> <span style="color:#221199">false</span>;       }   }</span></span>

（1）Consumer<T> : 消费型接口 void accept(T t); 示例：

<span style="background-color:#f8f8f8"><span style="color:#333333"><span style="color:#000000">public</span> <span style="color:#000000">static</span> <span style="color:#000000">void</span> <span style="color:#000000">main</span>(<span style="color:#000000">String</span>[] <span style="color:#000000">args</span>) {       <span style="color:#000000">happy</span>(<span style="color:#116644">1100</span>, (<span style="color:#000000">m</span>) <span style="color:#981a1a">-></span> <span style="color:#000000">System</span><span style="color:#116644">.</span><span style="color:#000000">out</span><span style="color:#116644">.</span><span style="color:#221199">println</span>(<span style="color:#aa1111">"本次吃饭,共消费："</span> <span style="color:#981a1a">+</span> <span style="color:#000000">m</span> <span style="color:#981a1a">+</span> <span style="color:#aa1111">"元"</span>));   }   <span style="color:#000000">public</span> <span style="color:#000000">static</span> <span style="color:#000000">void</span> <span style="color:#000000">happy</span>(<span style="color:#000000">Integer</span> <span style="color:#000000">money</span>, <span style="color:#000000">Consumer</span><span style="color:#981a1a"><</span><span style="color:#000000">Integer</span><span style="color:#981a1a">></span> <span style="color:#000000">con</span>) {       <span style="color:#000000">con</span><span style="color:#116644">.</span><span style="color:#000000">accept</span>(<span style="color:#000000">money</span>);
}</span></span>

（2）Supplier<T> : 供给型接口 T get(); 示例：

<span style="background-color:#f8f8f8"><span style="color:#333333"><span style="color:#aa5500">//Supplier<T> 供给型接口 :</span>    <span style="color:#000000">public</span> <span style="color:#000000">static</span> <span style="color:#000000">void</span> <span style="color:#000000">main</span>(<span style="color:#000000">String</span>[] <span style="color:#000000">args</span>) {       <span style="color:#000000">List</span><span style="color:#981a1a"><</span><span style="color:#000000">Integer</span><span style="color:#981a1a">></span> <span style="color:#000000">numList</span> <span style="color:#981a1a">=</span> <span style="color:#000000">getNumList</span>(<span style="color:#116644">5</span>, () <span style="color:#981a1a">-></span> (<span style="color:#770088">int</span>) (<span style="color:#000000">Math</span><span style="color:#116644">.</span><span style="color:#000000">random</span>() <span style="color:#981a1a">*</span> <span style="color:#116644">100</span>));       <span style="color:#770088">for</span> (<span style="color:#000000">Integer</span> <span style="color:#000000">num</span> : <span style="color:#000000">numList</span>) {           <span style="color:#000000">System</span><span style="color:#116644">.</span><span style="color:#000000">out</span><span style="color:#116644">.</span><span style="color:#221199">println</span>(<span style="color:#000000">num</span>);       }   }   <span style="color:#000000">public</span> <span style="color:#000000">static</span> <span style="color:#000000">List</span><span style="color:#981a1a"><</span><span style="color:#000000">Integer</span><span style="color:#981a1a">></span> <span style="color:#000000">getNumList</span>(<span style="color:#770088">int</span> <span style="color:#000000">num</span>, <span style="color:#000000">Supplier</span><span style="color:#981a1a"><</span><span style="color:#000000">Integer</span><span style="color:#981a1a">></span> <span style="color:#000000">sup</span>) {       <span style="color:#000000">List</span><span style="color:#981a1a"><</span><span style="color:#000000">Integer</span><span style="color:#981a1a">></span> <span style="color:#000000">list</span> <span style="color:#981a1a">=</span> <span style="color:#221199">new</span> <span style="color:#000000">ArrayList</span><span style="color:#981a1a"><></span>();       <span style="color:#770088">for</span> (<span style="color:#770088">int</span> <span style="color:#000000">i</span> <span style="color:#981a1a">=</span> <span style="color:#116644">0</span>; <span style="color:#000000">i</span> <span style="color:#981a1a"><</span> <span style="color:#000000">num</span>; <span style="color:#000000">i</span><span style="color:#981a1a">++</span>) {           <span style="color:#000000">Integer</span> <span style="color:#000000">n</span> <span style="color:#981a1a">=</span> <span style="color:#000000">sup</span><span style="color:#116644">.</span><span style="color:#000000">get</span>();           <span style="color:#000000">list</span><span style="color:#116644">.</span><span style="color:#000000">add</span>(<span style="color:#000000">n</span>);       }       <span style="color:#770088">return</span> <span style="color:#000000">list</span>;
} </span></span>

(3) Function<T, R> : 函数型接口 R apply(T t); 示例：

<span style="background-color:#f8f8f8"><span style="color:#333333"><span style="color:#000000">public</span> <span style="color:#000000">static</span> <span style="color:#000000">void</span> <span style="color:#000000">main</span>(<span style="color:#000000">String</span>[] <span style="color:#000000">args</span>) {   <span style="color:#000000">String</span> <span style="color:#000000">newStr</span> <span style="color:#981a1a">=</span> <span style="color:#000000">strHandler</span>(<span style="color:#aa1111">"\t\t\t 五一四天乐 "</span>, (<span style="color:#000000">str</span>) <span style="color:#981a1a">-></span> <span style="color:#000000">str</span><span style="color:#116644">.</span><span style="color:#000000">trim</span>());   <span style="color:#000000">System</span><span style="color:#116644">.</span><span style="color:#000000">out</span><span style="color:#116644">.</span><span style="color:#221199">println</span>(<span style="color:#000000">newStr</span>);   <span style="color:#000000">String</span> <span style="color:#000000">subStr</span> <span style="color:#981a1a">=</span> <span style="color:#000000">strHandler</span>(<span style="color:#aa1111">"我一定要做数据挖掘"</span>, (<span style="color:#000000">str</span>) <span style="color:#981a1a">-></span> <span style="color:#000000">str</span><span style="color:#116644">.</span><span style="color:#000000">substring</span>(<span style="color:#116644">2</span>, <span style="color:#116644">5</span>));   <span style="color:#000000">System</span><span style="color:#116644">.</span><span style="color:#000000">out</span><span style="color:#116644">.</span><span style="color:#221199">println</span>(<span style="color:#000000">subStr</span>);
}
<span style="color:#aa5500">// 需求：用于处理字符串</span>
<span style="color:#000000">public</span> <span style="color:#000000">static</span> <span style="color:#000000">String</span> <span style="color:#000000">strHandler</span>(<span style="color:#000000">String</span> <span style="color:#000000">str</span>, <span style="color:#000000">Function</span><span style="color:#981a1a"><</span><span style="color:#000000">String</span>, <span style="color:#000000">String</span><span style="color:#981a1a">></span> <span style="color:#000000">fun</span>) {   <span style="color:#770088">return</span> <span style="color:#000000">fun</span><span style="color:#116644">.</span><span style="color:#000000">apply</span>(<span style="color:#000000">str</span>);
}</span></span>

(4) Predicate<T> : 断言型接口 boolean test(T t); 示例：

<span style="background-color:#f8f8f8"><span style="color:#333333"><span style="color:#000000">public</span> <span style="color:#000000">static</span> <span style="color:#000000">void</span> <span style="color:#000000">main</span>(<span style="color:#000000">String</span>[] <span style="color:#000000">args</span>) {   <span style="color:#000000">List</span><span style="color:#981a1a"><</span><span style="color:#000000">String</span><span style="color:#981a1a">></span> <span style="color:#000000">list</span> <span style="color:#981a1a">=</span> <span style="color:#000000">Arrays</span><span style="color:#116644">.</span><span style="color:#000000">asList</span>(<span style="color:#aa1111">"Hello"</span>, <span style="color:#aa1111">"WWW"</span>, <span style="color:#aa1111">"Lambda"</span>, <span style="color:#aa1111">"!!"</span>, <span style="color:#aa1111">"ok"</span>);   <span style="color:#000000">List</span><span style="color:#981a1a"><</span><span style="color:#000000">String</span><span style="color:#981a1a">></span> <span style="color:#000000">strList</span> <span style="color:#981a1a">=</span> <span style="color:#000000">filterStr</span>(<span style="color:#000000">list</span>, (<span style="color:#