lambda表达式10个示例——学习笔记

时间 2020-05-06

标签 lambda 表达式示例学习笔记繁體版

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<div class=" "> <p>摘录：http://www.importnew.com/16436.html</p> <h2>一、lambda实现Runnable</h2> <div class="cnblogs_code"><div class="cnblogs_code_toolbar"><span class="cnblogs_code_copy"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></span></div> <pre><span style="color: #008000;">//</span><span style="color: #008000;"> Java 8以前：</span> <span style="color: #0000ff;">new</span> Thread(<strong><span style="color: #ff0000;">new Runnable() { @Override public void</span></strong><span style="color: #000000;"><strong><span style="color: #ff0000;"> run</span></strong>() { System.out.println(</span>"Before Java8, too much code for too little to do"<span style="color: #000000;">); } }).start();</span></pre> <div class="cnblogs_code_toolbar"><span class="cnblogs_code_copy"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></span></div></div> <div class="cnblogs_code"> <pre><span style="color: #008000;">//</span><span style="color: #008000;">Java 8方式：<span style="color: #ff0000;">用() -> {}代码块替代了整个<span style="color: #ff0000;">匿名类</span></span></span> <span style="color: #0000ff;">new</span> Thread(<span style="color: #ff0000;"><strong> () -></strong></span> System.out.println("In Java8, Lambda expression rocks !!") ).start();</pre> </div> <p>output:</p> <div class="cnblogs_code"> <pre>too much code, <span style="color: #0000ff;">for</span> too little to <span style="color: #0000ff;">do</span><span style="color: #000000;"> Lambda expression rocks </span>!!</pre> </div> <p>若是你的方法不对参数进行修改、重写，只是在控制台打印点东西的话，那么能够这样写：</p> <div class="cnblogs_code"> <pre>() -> System.out.println("Hello Lambda Expressions");</pre> </div> <p>若是你的方法接收两个参数，那么能够写成以下这样：</p> <div class="cnblogs_code"> <pre>若是你的方法接收两个参数，那么能够写成以下这样：</pre> </div> <h2>二、使用Java 8 lambda表达式进行事件处理</h2> <p>编写事件监听：</p> <div class="cnblogs_code"><div class="cnblogs_code_toolbar"><span class="cnblogs_code_copy"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></span></div> <pre><span style="color: #008000;">//</span><span style="color: #008000;"> Java 8以前：</span> JButton show = <span style="color: #0000ff;">new</span> JButton("Show"<span style="color: #000000;">); show.addActionListener(</span><strong><span style="color: #ff0000;">new ActionListener() { @Override public void</span></strong><span style="color: #000000;"><strong><span style="color: #ff0000;"> actionPerformed</span></strong>(ActionEvent e) { System.out.println(</span>"Event handling without lambda expression is boring"<span style="color: #000000;">); } });</span></pre> <div class="cnblogs_code_toolbar"><span class="cnblogs_code_copy"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></span></div></div> <div class="cnblogs_code"> <pre><span style="color: #008000;">//</span><span style="color: #008000;"> Java 8方式：</span> show.addActionListener(<strong><span style="color: #ff0000;">(e) -></span></strong><span style="color: #000000;"> { System.out.println(</span>"Light, Camera, Action !! Lambda expressions Rocks"<span style="color: #000000;">); });</span></pre> </div> <p>output：</p> <div class="cnblogs_code"> <pre>too much code, <span style="color: #0000ff;">for</span> too little to <span style="color: #0000ff;">do</span><span style="color: #000000;"> Lambda expression rocks </span>!!</pre> </div> <h2>三、使用lambda表达式对列表进行迭代</h2> <div class="cnblogs_code"> <pre><span style="color: #008000;">//</span><span style="color: #008000;"> Java 8以前：</span> List features = Arrays.asList("Lambdas", "Default Method", "Stream API", "Date and Time API"<span style="color: #000000;">); </span><span style="color: #0000ff;">for</span><span style="color: #000000;"> (String feature : features) { System.out.println(feature); }</span></pre> </div> <div class="cnblogs_code"><div class="cnblogs_code_toolbar"><span class="cnblogs_code_copy"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></span></div> <pre><span style="color: #008000;">//</span><span style="color: #008000;"> Java 8以后：</span> List features = Arrays.asList("Lambdas", "Default Method", "Stream API", "Date and Time API"<span style="color: #000000;">); features.forEach(n </span>-><span style="color: #000000;"> System.out.println(n));html

</span><span style="color: #008000;">//</span><span style="color: #008000;"> 使用Java 8的方法引用更方便，<span style="color: #ff0000;">方法引用由::双冒号操做符标示， </span></span><span style="color: #008000;">//</span><span style="color: #008000;"> 看起来像C++的做用域解析运算符</span> features.forEach(System.out::println);</pre>java

System.out.println(</span>"Languages which starts with J :"<span style="color: #000000;">);
filter(languages, <strong><span style="color: #ff0000;">(str)</span></strong></span><strong><span style="color: #ff0000;">-&gt;</span></strong>str.startsWith("J"<span style="color: #000000;">));

System.out.println(</span>"Languages which ends with a "<span style="color: #000000;">);
filter(languages, <span style="color: #ff0000;"><strong>(str)</strong></span></span><span style="color: #ff0000;"><strong>-&gt;</strong></span>str.endsWith("a"<span style="color: #000000;">));

System.out.println(</span>"Print all languages :"<span style="color: #000000;">);
filter(languages, <strong><span style="color: #ff0000;">(str)</span></strong></span><strong><span style="color: #ff0000;">-&gt;</span></strong><span style="color: #0000ff;">true</span><span style="color: #000000;">);

System.out.println(</span>"Print no language : "<span style="color: #000000;">);
filter(languages, <strong><span style="color: #ff0000;">(str)</span></strong></span><strong><span style="color: #ff0000;">-&gt;</span></strong><span style="color: #0000ff;">false</span><span style="color: #000000;">);

System.out.println(</span>"Print language whose length greater than 4:"<span style="color: #000000;">);
filter(languages, <span style="color: #ff0000;"><strong>(str)</strong></span></span><span style="color: #ff0000;"><strong>-&gt;</strong></span>str.length() &gt; 4<span style="color: #000000;">);

}shell

</span><span style="color: #008000;">//</span><span style="color: #008000;"> 使用lambda表达式</span> List costBeforeTax = Arrays.asList(100, 200, 300, 400, 500<span style="color: #000000;">); costBeforeTax.stream().map((cost) </span>-> cost + .12*cost).forEach(System.out::println);</pre>微信

</span><span style="color: #008000;">//</span><span style="color: #008000;"> 新方法：<span style="color: #ff0000;">能够用内建方法，也能够本身定义</span></span> List costBeforeTax = Arrays.asList(100, 200, 300, 400, 500<span style="color: #000000;">); </span><span style="color: #0000ff;">double</span> bill = costBeforeTax.stream().map((cost) -> cost + .12*cost)<strong><span style="color: #ff0000;">.reduce((sum, cost) -> sum +</span></strong><span style="color: #000000;"><strong><span style="color: #ff0000;"> cost)</span></strong>.get(); System.out.println(</span>"Total : " + bill);</pre>闭包

<div class="cnblogs_code_toolbar"><span class="cnblogs_code_copy"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></span></div></div> <p>output:</p> <div class="cnblogs_code"> <pre>Total : 1680.0<span style="color: #000000;"> Total : </span>1680.0</pre> </div> <h2>七、经过<span style="color: #ff0000;">过滤</span>建立一个String列表</h2> <div class="cnblogs_code"> <pre><span style="color: #008000;">//</span><span style="color: #008000;"> 建立一个字符串列表，每一个字符串长度大于2</span> List<String> filtered = strList.stream()<strong><span style="color: #ff0000;">.filter(x -> x.length()> 2</span></strong><span style="color: #000000;"><strong><span style="color: #ff0000;">).</span></strong>collect(Collectors.toList()); System.out.printf(</span>"Original List : %s, filtered list : %s %n", strList, filtered);</pre> </div> <p>output:</p> <div class="cnblogs_code"> <pre>Original List : [abc, , bcd, , defg, jk], filtered list : [abc, bcd, defg]</pre> </div> <h2>八、对列表的<span style="color: #ff0000;">每一个元素应用函数</span></h2> <div class="cnblogs_code"> <pre><span style="color: #008000;">//</span><span style="color: #008000;"> 将字符串换成大写并用逗号连接起来</span> List<String> G7 = Arrays.asList("USA", "Japan", "France", "Germany", "Italy", "U.K.","Canada"<span style="color: #000000;">); String G7Countries </span>= G7.stream()<strong><span style="color: #ff0000;">.map(x -> x.toUpperCase())</span></strong>.collect(Collectors.joining(", "<span style="color: #000000;">)); System.out.println(G7Countries);</span></pre> </div> <h2>九、复制不一样的值，建立一个子列表</h2> <div class="cnblogs_code"> <pre><span style="color: #008000;">//</span><span style="color: #008000;"> 用全部不一样的数字建立一个正方形列表</span> List<Integer> numbers = Arrays.asList(9, 10, 3, 4, 7, 3, 4<span style="color: #000000;">); List</span><Integer> distinct = numbers.stream()<span style="color: #ff0000;"><strong>.map( i -> i*</strong></span><span style="color: #000000;"><span style="color: #ff0000;"><strong>i)</strong></span>.distinct().collect(Collectors.toList()); System.out.printf(</span>"Original List : %s, Square Without duplicates : %s %n", numbers, distinct);</pre> </div> <p>output:</p> <div class="cnblogs_code"> <pre>Original List : [9, 10, 3, 4, 7, 3, 4], Square Without duplicates : [81, 100, 9, 16, 49]</pre> </div> <h2>十、计算集合元素的最大值、最小值、总和以及平均值</h2> <p>ntStream、LongStream 和 DoubleStream 等流的类中，有个很是有用的方法叫作 summaryStatistics() 。能够返回 IntSummaryStatistics、LongSummaryStatistics 或者 DoubleSummaryStatistic s，描述流中元素的各类摘要数据。</p> <p>最大值　　最小值　　全部元素的总和　　平均值</p> <div class="cnblogs_code"><div class="cnblogs_code_toolbar"><span class="cnblogs_code_copy"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></span></div> <pre><span style="color: #008000;">//</span><span style="color: #008000;">获取数字的个数、最小值、最大值、总和以及平均值</span> List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29<span style="color: #000000;">); IntSummaryStatistics stats </span>= primes.stream().mapToInt((x) -><span style="color: #000000;"> x).summaryStatistics(); System.out.println(</span>"Highest prime number in List : " +<span style="color: #000000;"> stats.getMax()); System.out.println(</span>"Lowest prime number in List : " +<span style="color: #000000;"> stats.getMin()); System.out.println(</span>"Sum of all prime numbers : " +<span style="color: #000000;"> stats.getSum()); System.out.println(</span>"Average of all prime numbers : " + stats.getAverage());</pre> <div class="cnblogs_code_toolbar"><span class="cnblogs_code_copy"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></span></div></div> <p>输出：</p> <div class="cnblogs_code"> <pre>Highest prime number in List : 29<span style="color: #000000;"> Lowest prime number in List : </span>2<span style="color: #000000;"> Sum of all prime numbers : </span>129<span style="color: #000000;"> Average of all prime numbers : </span>12.9</pre> </div> <h2>Lambda表达式 vs 匿名类</h2> <p>既然lambda表达式即将正式取代Java代码中的匿名内部类，那么有必要对两者作一个比较分析。</p> <p><span style="color: #ff0000;">一个关键的不一样点就是关键字 this:</span></p> <p>匿名类的 this 关键字指向匿名类，而lambda表达式的 this 关键字指向包围lambda表达式的类。</p> <p><span style="color: #ff0000;">另外一个不一样点是两者的编译方式:</span></p> <p>Java编译器将lambda表达式编译成类的私有方法。使用了Java 7的 invokedynamic 字节码指令来动态绑定这个方法</p> <h1>注意：</h1> <p>1）lambda表达式仅能放入以下代码：<span style="color: #ff0000;">预约义使用了 @Functional 注释的函数式接口，自带一个抽象函数的方法</span>，或者SAM（Single Abstract Method 单个抽象方法）类型。这些称为lambda表达式的目标类型，能够用做返回类型，或lambda目标代码的参数。例如，若一个方法接收Runnable、Comparable或者 Callable 接口，都有单个抽象方法，能够传入lambda表达式。相似的，若是一个方法接受声明于 java.util.function 包内的接口，例如 Predicate、Function、Consumer 或 Supplier，那么能够向其传lambda表达式。</p> <p>2）lambda表达式内可使用方法引用，仅当该方法不修改lambda表达式提供的参数。本例中的lambda表达式能够换为方法引用，由于这仅是一个参数相同的简单方法调用。</p> <div class="cnblogs_code"> <pre>list.forEach(n -><span style="color: #000000;"> System.out.println(n)); list.forEach(System.out::println); </span><span style="color: #008000;">//</span><span style="color: #008000;"> 使用方法引用</span></pre> </div> <div> </div> <p>然而，若对参数有任何修改，则不能使用方法引用，而需键入完整地lambda表达式，以下所示：</p> <div> <div id="highlighter_697471" class="syntaxhighlighter notranslate java"> <div class="cnblogs_code"> <pre>list.forEach((String s) -> System.out.println("*" + s + "*"));</pre> </div> </div> </div> <p>事实上，能够省略这里的lambda参数的类型声明，<strong><span style="color: #ff0000;">编译器能够从列表的类属性推测出来。</span></strong></p> <p>3）lambda内部可使用<span style="color: #ff0000;">静态、非静态和局部变量</span>，这称为lambda内的变量捕获。</p> <p>4）Lambda表达式在Java中又称为闭包或匿名函数，因此若是有同事把它叫闭包的时候，不用惊讶。</p> <p>5）<span style="color: #ff0000;">Lambda方法在编译器内部被翻译成私有方法，并派发 invokedynamic 字节码指令来进行调用。</span>可使用JDK中的 javap 工具来反编译class文件。使用 javap -p 或 javap -c -v 命令来看一看lambda表达式生成的字节码。大体应该长这样：</p> <div> <div id="highlighter_135526" class="syntaxhighlighter notranslate java"> <div class="cnblogs_code"> <pre><span style="color: #0000ff;">private</span> <span style="color: #0000ff;">static</span> java.lang.Object lambda$0(java.lang.String);</pre> </div> </div> </div> <p>6）lambda表达式有个限制，那就是只能引用 final 或 final 局部变量，<span style="color: #ff0000;">这就是说不能在lambda内部修改定义在域外的变量。</span></p> <div class="cnblogs_code"> <pre>List<Integer> primes = Arrays.asList(<span style="color: #0000ff;">new</span> Integer[]{2, 3,5,7<span style="color: #000000;">}); </span><span style="color: #0000ff;">int</span> factor = 2<span style="color: #000000;">; primes.forEach(element </span>-> { factor++; });</pre> </div> <div class="cnblogs_code"> <pre><span style="color: #ff0000;">Compile time error : "local variables referenced from a lambda expression must be final or effectively final"</span></pre> </div> <div> </div> <p>另外，只是访问它而不做修改是能够的，以下所示：</p> <div> <div id="highlighter_719558" class="syntaxhighlighter notranslate java"> <div class="cnblogs_code"> <pre>List<Integer> primes = Arrays.asList(<span style="color: #0000ff;">new</span> Integer[]{2, 3,5,7<span style="color: #000000;">}); </span><span style="color: #0000ff;">int</span> factor = 2<span style="color: #000000;">; primes.forEach(element </span>-> { System.out.println(factor*element); })</pre> </div> </div> </div> <p>输出：</p> <div> <div id="highlighter_773319" class="syntaxhighlighter notranslate shell"> <div class="cnblogs_code"> <pre>4 6 10 14</pre> </div> <p> </p> </div> </div> </div> <div id="MySignature"></div> <div class="clear"></div> <div id="blog_post_info_block"><div id="BlogPostCategory"> 分类: <a href="https://www.cnblogs.com/L-a-u-r-a/category/1221830.html" target="_blank">JDK8新特性</a></div> <div id="EntryTag"> 标签: <a href="https://www.cnblogs.com/L-a-u-r-a/tag/JDK8/">JDK8</a>, <a href="https://www.cnblogs.com/L-a-u-r-a/tag/Java/">Java</a></div>

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<div> <p style="text-align: center;"><strong><span style="font-size: 14pt;">Java 8 Lambda表达式和理解</span></strong></p> <p style="text-align: right;">说明：部分资料来源于网络</p> <p style="text-align: right;">时间：20190704</p> <p>Lambda 表达式，也可称为闭包，它是推进 Java 8 发布的最重要新特性。<strong>Lambda 容许把函数做为一个方法的参数（函数做为参数传递进方法中）</strong><span style="font-family: Helvetica;">。使用</span> Lambda 表达式可使代码变的更加简洁紧凑。</p> <p> </p> <p style="text-align: center;"><span style="background-color: #c0c0c0;"><strong><span style="font-size: 18px;">1、语法</span></strong></span></p> <p class="p">一、lambda 表达式的语法格式以下：</p> <p class="p"><strong><span style="font-family: 宋体;">　　（左边）</span></strong><strong><span style="font-family: 宋体;">输入参数</span></strong><strong>->（右边）</strong><strong>lambda主体</strong></p> <div class="cnblogs_code"> <pre>(parameters) -> expression;</pre> </div> <p><span style="font-family: Consolas;">　　或</span></p> <div class="cnblogs_code"> <pre>(parameters) ->{ statements; }</pre> </div> <p> </p> <p class="p"><span style="font-family: Helvetica;">二、如下是</span>lambda表达式的重要特征:</p> <p class="p"><span style="font-family: 宋体;">（1）输入参数：</span></p> <p><strong><span style="font-family: Helvetica;">　　可选类型声明：</span></strong><strong><span style="font-family: Helvetica;">不须要声明参数类型</span></strong><span style="font-family: Helvetica;">，编译器能够统一识别参数值。</span></p> <p><strong><span style="font-family: Helvetica;">　　可选的参数圆括号：</span></strong></p> <p>　　　　a、<strong><span style="font-family: Helvetica;">一个参数无需定义圆括号，但多个参数须要定义圆括号。</span></strong></p> <p>　　　　b、<strong><span style="font-family: 宋体;">若是申明了参数类型，则必定须要圆括号。</span></strong></p> <p>（2）lambda主体<span style="font-family: 宋体;">：</span></p> <p><strong><span style="font-family: Helvetica;">　　可选的大括号：</span></strong><span style="font-family: Helvetica;">若是主体包含了一个语句，就不须要使用大括号。</span></p> <p><strong><span style="font-family: Helvetica;">　　可选的返回关键字：</span></strong><span style="font-family: Helvetica;">若是主体只有一个表达式返回值则编译器会自动返回值，</span><strong><span style="font-family: Helvetica;">大括号须要指定明表达式返回了一个数值</span></strong><span style="font-family: Helvetica;">。</span></p> <p> </p> <p><span style="font-family: 宋体;">三、按照上面的格式，</span>lambda<span style="font-family: 宋体;">不一样参数的表达式写法</span></p> <p>（1）<span style="font-family: 宋体;">没有参数的表达式：</span></p> <div class="cnblogs_code"> <pre>() -> System.out.println("this is no parameter Lambda expression");</pre> </div> <p>（2）只有一个参数的表达式：</p> <div class="cnblogs_code"> <pre>(x) -> System.out.println("this is only one parameter Lambda expression");</pre> </div> <p>　　或者</p> <div class="cnblogs_code"> <pre>(X x) -> System.out.println("this is only one parameter Lambda expression"<span style="color: #000000;">);</span></pre> </div> <p><span style="font-family: 宋体;">　　和</span></p> <div class="cnblogs_code"> <pre>(x) -><span style="color: #000000;"> { x </span>= x*2<span style="color: #000000;">; System.out.println(</span>"this is only one parameter Lambda expression"<span style="color: #000000;">); System.out.println(</span>"the function is double input value"<span style="color: #000000;">); </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> x; };</span></pre> </div> <p><span style="font-family: 宋体;">　　说明：一个参数的能够不用使用</span>()<span style="font-family: 宋体;">，若是参数声明了参数类型则必需要加</span><span style="font-family: Calibri;">()</span><span style="font-family: 宋体;">；</span><span style="font-family: Calibri;">Lambda</span><span style="font-family: 宋体;">主体是语句块的话须要使用</span><span style="font-family: Calibri;">{}</span><span style="font-family: 宋体;">。</span></p> <p>（3）有两个或者多个参数的表达式：</p> <div class="cnblogs_code"> <pre>(x,y) -> System.out.println("these are several parameters Lambda expression");</pre> </div> <p>　　或者</p> <div class="cnblogs_code"> <pre>(X x,Y y) -><span style="color: #000000;"> { 　　System.out.println(</span>"the function is add two input values"<span style="color: #000000;">); 　　System.out.println(</span>"these are several parameters Lambda expression"<span style="color: #000000;">); 　　</span><span style="color: #0000ff;">return</span> x+<span style="color: #000000;">y; };</span></pre> </div> <p><span style="font-family: 宋体;">　　说明：有多个参数的</span>lambda<span style="font-family: 宋体;">表达式，参数使用</span><span style="font-family: Calibri;">,</span><span style="font-family: 宋体;">隔开。</span><span style="font-family: Calibri;">Lambda</span><span style="font-family: 宋体;">主体是语句块的话须要使用</span><span style="font-family: Calibri;">{}</span><span style="font-family: 宋体;">。</span></p> <p> </p> <p style="text-align: center;"><span style="background-color: #c0c0c0;"><strong><span style="font-size: 18px;">2、Lambda 表达式实例</span></strong></span></p> <p>lambda示例1：</p> <div class="cnblogs_code"><div class="cnblogs_code_toolbar"><span class="cnblogs_code_copy"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></span></div> <pre><span style="color: #008000;">/*</span><span style="color: #008000;"> * Predicate<T>接口中boolean test(T t)方法只接收一个参数，返回值为boolean类型， * 故lambda表达式的输入参数只有一个参数:x，lambda的主体返回值为boolean类型 </span><span style="color: #008000;">*/</span><span style="color: #000000;"> Predicate</span><Integer> atLeast5 = x -> x >= 5<span style="color: #000000;">; System.out.println(</span>"传入参数是否大于5：" + atLeast5.test(6<span style="color: #000000;">));

</span><span style="color: #008000;">/*</span><span style="color: #008000;">

BinaryOperator<T>接口中R apply(T t, U u)方法接收两个泛型参数，返回值为也为泛型
故lambda表达式输入Long参数有两个：x,y，lambda的主体返回值为Long类型 </span><span style="color: #008000;">*/</span><span style="color: #000000;"> BinaryOperator</span><Long> addLongs = (x, y) -><span style="color: #000000;"> { 　　Long z </span>= x +<span style="color: #000000;"> y; 　　</span><span style="color: #0000ff;">return</span><span style="color: #000000;"> z; }; System.out.println(</span>"计算传入两个Long参数的和：" + addLongs.apply(5l, 6l<span style="color: #000000;">));

</span><span style="color: #008000;">/*</span><span style="color: #008000;">

Runnable接口中run()方法没有参数，有没有返回值，故lambda表达式没有参数，lambda主体也没有返回值 </span><span style="color: #008000;">*/</span><span style="color: #000000;"> Runnable run1 </span>= () -> System.out.println("这个方法就是run里面的方法"<span style="color: #000000;">); run1.run();

</span><span style="color: #0000ff;">try</span><span style="color: #000000;"> { 　　</span><span style="color: #0000ff;">final</span> Integer value = 9<span style="color: #000000;">; 　　</span><span style="color: #008000;">/</span><span style="color: #008000;"> 　　 * 一、Callable<V>接口中V call() throws Exception方法没有参数，故lambda表达式也不能有输入参数, 　　 * 返回类型为泛型，故lambda主体须要返回指定Integer类型　　 * 二、由于.call()方法抛出异常，因此须要抛出或者捕获异常　　 * 三、lambda表达式使用外部参数，须要是final类型，及时外部参数没有定义为final类型，　　 * 也会隐式的指定为final，故值或者引用地址不能修改。　　 </span><span style="color: #008000;">/</span><span style="color: #000000;"> 　　Callable</span><Integer> call = () -><span style="color: #000000;"> value; 　　System.out.println(</span>"无参的方法，因此lambda的参数列表中不能传递参数：" +<span style="color: #000000;"> call.call()); } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (Exception e) { 　　e.printStackTrace(); }</span></pre>

　　</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String args[]){ <br> 　　　　Java8Tester tester </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Java8Tester(); 　　　　</span><span style="color: #008000;">//</span><span style="color: #008000;"> 类型声明 </span> 　　　　MathOperation addition = (<span style="color: #0000ff;">int</span> a, <span style="color: #0000ff;">int</span> b) -> a +<span style="color: #000000;"> b; 　　　　</span><span style="color: #008000;">//</span><span style="color: #008000;"> 不用类型声明 </span> 　　　　MathOperation subtraction = (a, b) -> a -<span style="color: #000000;"> b; 　　　　</span><span style="color: #008000;">//</span><span style="color: #008000;"> 大括号中的返回语句 </span> 　　　　MathOperation multiplication = (<span style="color: #0000ff;">int</span> a, <span style="color: #0000ff;">int</span> b) -> { <span style="color: #0000ff;">return</span> a *<span style="color: #000000;"> b; }; 　　　　</span><span style="color: #008000;">//</span><span style="color: #008000;"> 没有大括号及返回语句 </span> 　　　　MathOperation division = (<span style="color: #0000ff;">int</span> a, <span style="color: #0000ff;">int</span> b) -> a /<span style="color: #000000;"> b;

　　　　System.out.println(</span>"10 + 5 = " + tester.operate(10, 5<span style="color: #000000;">, addition)); 　　　　System.out.println(</span>"10 - 5 = " + tester.operate(10, 5<span style="color: #000000;">, subtraction)); 　　　　System.out.println(</span>"10 x 5 = " + tester.operate(10, 5<span style="color: #000000;">, multiplication)); 　　　　System.out.println(</span>"10 / 5 = " + tester.operate(10, 5<span style="color: #000000;">, division));

　　　　</span><span style="color: #008000;">//</span><span style="color: #008000;"> 不用括号 </span> 　　　　GreetingService greetService1 = message -> System.out.println("Hello " +<span style="color: #000000;"> message); 　　　　</span><span style="color: #008000;">//</span><span style="color: #008000;"> 用括号 </span> 　　　　GreetingService greetService2 = (message) -> System.out.println("Hello " +<span style="color: #000000;"> message);

　　　　greetService1.sayMessage(</span>"Runoob"<span style="color: #000000;">); 　　　　greetService2.sayMessage(</span>"Google"<span style="color: #000000;">); 　　}<br><br>　　// 定义接口和接口中为实现的方法　　</span><span style="color: #0000ff;">interface</span> MathOperation {<br><span style="color: #0000ff;">　　　　int</span> operation(<span style="color: #0000ff;">int</span> a, <span style="color: #0000ff;">int</span><span style="color: #000000;"> b);<br>　　}<br><br></span></pre>

<pre><span>　　// 定义接口和接口中为实现的方法<br></span><span style="color: #0000ff;">　　interface</span> GreetingService {<br><span style="color: #0000ff;">　　　　void</span><span> sayMessage(String message);<br></span><em id="__mceDel"><em id="__mceDel"><em id="__mceDel"><span>　　} </span></em></em></em></pre>

<pre><em id="__mceDel"><em id="__mceDel"><em id="__mceDel"><span style="color: #000000;"><br>　　// 定义方法，方法经过lambda表达式实现了接口中的方法　　</span><span style="color: #0000ff;">private</span> <span style="color: #0000ff;">int</span> operate(<span style="color: #0000ff;">int</span> a, <span style="color: #0000ff;">int</span><span style="color: #000000;"> b, MathOperation mathOperation){ 　　　　</span><span style="color: #0000ff;">return</span><span style="color: #000000;"> mathOperation.operation(a, b); 　　} }</span></em></em></em></pre>

</span><span style="color: #0000ff;">　　final</span> <span style="color: #0000ff;">static</span> String salutation = "Hello! "<span style="color: #000000;">;

</span><span style="color: #0000ff;">　　public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String args[]){<br> 　　　　GreetingService greetService1 </span>= message -> System.out.println(salutation +<span style="color: #000000;"> message); 　　　　greetService1.sayMessage(</span>"Runoob"<span style="color: #000000;">);

　　　　</span><span style="color: #008000;">//</span><span style="color: #008000;">====================至关于下面==============================</span> 　　　　GreetingService g = <span style="color: #0000ff;">new</span><span style="color: #000000;"> GreetingService() { 　　　　　　@Override </span><span style="color: #0000ff;">　　　　　　public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> sayMessage(String message) { 　　　　　　　　System.out.println(salutation </span>+<span style="color: #000000;"> message); 　　　　　　} 　　　　}; 　　　　g.sayMessage(</span>"jack"<span style="color: #000000;">);<br> 　　}

　　</span><span style="color: #0000ff;">interface</span><span style="color: #000000;"> GreetingService { 　　　　</span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sayMessage(String message); 　　} } </span></pre>

　　</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">interface</span> Converter<T1, T2><span style="color: #000000;"> { 　　　　</span><span style="color: #0000ff;">void</span> convert(<span style="color: #0000ff;">int</span><span style="color: #000000;"> i); 　　} }</span></pre>

<div class="cnblogs_code_toolbar"><span class="cnblogs_code_copy"><a href="javascript:void(0);" onclick="copyCnblogsCode(this)" title="复制代码"><img src="//common.cnblogs.com/images/copycode.gif" alt="复制代码"></a></span></div></div> <p class="p">lambda表达式的局部变量能够不声明为final，可是不可被后面的代码修改（即隐性的具备final 的语义）</p> <div class="cnblogs_code"> <pre><span style="color: #0000ff;">int</span> num = 1<span style="color: #000000;">; Converter</span><Integer, String> s = (param) -> System.out.println(String.valueOf(param +<span style="color: #000000;"> num)); s.convert(</span>2<span style="color: #000000;">); num </span>= 5; <span style="color: #008000;">//</span><span style="color: #008000;">报错信息：Local variable num defined in an enclosing scope must be final or effectively final</span></pre> </div> <p class="p"><span style="font-family: Helvetica;">在</span> Lambda 表达式当中不容许声明一个与局部变量同名的参数或者局部变量。</p> <div class="cnblogs_code"> <pre>String first = ""<span style="color: #000000;">; Comparator</span><String> comparator = (first, second) -> Integer.compare(first.length(), second.length()); <span style="color: #008000;">//</span><span style="color: #008000;">编译会出错</span></pre> </div> <p> </p> </div>