无涯教程-Java8 - Lambda表达式

无涯教程
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Lambda表达式是在Java8中引入的，被吹捧为Java 8最大的特性。Lambda表达式简化了函数式编程，并大大简化了开发。

lambda表达式的特征在于以下语法。

parameter -> expression body

Lambda表达式

使用您选择的任何编辑器(例如，C:\> JAVA)创建以下Java程序。

Java8Tester.java

public class Java8Tester {

public static void main(String args[]) {
Java8Tester tester=new Java8Tester();


  </span><span class="com">//类型声明</span><span class="pln">
  </span><span class="typ">MathOperation</span><span class="pln"> addition</span><span class="pun">=(</span><span class="kwd">int</span><span class="pln"> a</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">int</span><span class="pln"> b</span><span class="pun">)</span><span class="pln"> </span><span class="pun">-&gt;</span><span class="pln"> a </span><span class="pun">+</span><span class="pln"> b</span><span class="pun">;</span><span class="pln">
	
  </span><span class="com">//自动推断声明</span><span class="pln">
  </span><span class="typ">MathOperation</span><span class="pln"> subtraction</span><span class="pun">=(</span><span class="pln">a</span><span class="pun">,</span><span class="pln"> b</span><span class="pun">)</span><span class="pln"> </span><span class="pun">-&gt;</span><span class="pln"> a </span><span class="pun">-</span><span class="pln"> b</span><span class="pun">;</span><span class="pln">
	
  </span><span class="com">//返回声明以及{}花括号</span><span class="pln">
  </span><span class="typ">MathOperation</span><span class="pln"> multiplication</span><span class="pun">=(</span><span class="kwd">int</span><span class="pln"> a</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">int</span><span class="pln"> b</span><span class="pun">)</span><span class="pln"> </span><span class="pun">-&gt;</span><span class="pln"> </span><span class="pun">{</span><span class="pln"> </span><span class="kwd">return</span><span class="pln"> a </span><span class="pun">*</span><span class="pln"> b</span><span class="pun">;</span><span class="pln"> </span><span class="pun">};</span><span class="pln">
	
  </span><span class="com">//没有返回声明，没有{}花括号</span><span class="pln">
  </span><span class="typ">MathOperation</span><span class="pln"> division</span><span class="pun">=(</span><span class="kwd">int</span><span class="pln"> a</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">int</span><span class="pln"> b</span><span class="pun">)</span><span class="pln"> </span><span class="pun">-&gt;</span><span class="pln"> a</span><span class="pun">/</span><span class="pln">b</span><span class="pun">;</span><span class="pln">
	
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"10 + 5="</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> tester</span><span class="pun">.</span><span class="pln">operate</span><span class="pun">(</span><span class="lit">10</span><span class="pun">,</span><span class="pln"> </span><span class="lit">5</span><span class="pun">,</span><span class="pln"> addition</span><span class="pun">));</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"10 - 5="</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> tester</span><span class="pun">.</span><span class="pln">operate</span><span class="pun">(</span><span class="lit">10</span><span class="pun">,</span><span class="pln"> </span><span class="lit">5</span><span class="pun">,</span><span class="pln"> subtraction</span><span class="pun">));</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"10 x 5="</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> tester</span><span class="pun">.</span><span class="pln">operate</span><span class="pun">(</span><span class="lit">10</span><span class="pun">,</span><span class="pln"> </span><span class="lit">5</span><span class="pun">,</span><span class="pln"> multiplication</span><span class="pun">));</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"10/5="</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> tester</span><span class="pun">.</span><span class="pln">operate</span><span class="pun">(</span><span class="lit">10</span><span class="pun">,</span><span class="pln"> </span><span class="lit">5</span><span class="pun">,</span><span class="pln"> division</span><span class="pun">));</span><span class="pln">
	
  </span><span class="com">//without parenthesis</span><span class="pln">
  </span><span class="typ">GreetingService</span><span class="pln"> greetService1</span><span class="pun">=</span><span class="pln">message </span><span class="pun">-&gt;</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Hello "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> message</span><span class="pun">);</span><span class="pln">
	
  </span><span class="com">//with parenthesis</span><span class="pln">
  </span><span class="typ">GreetingService</span><span class="pln"> greetService2</span><span class="pun">=(</span><span class="pln">message</span><span class="pun">)</span><span class="pln"> </span><span class="pun">-&gt;</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Hello "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> message</span><span class="pun">);</span><span class="pln">
	
  greetService1</span><span class="pun">.</span><span class="pln">sayMessage</span><span class="pun">(</span><span class="str">"Mahesh"</span><span class="pun">);</span><span class="pln">
  greetService2</span><span class="pun">.</span><span class="pln">sayMessage</span><span class="pun">(</span><span class="str">"Suresh"</span><span class="pun">);</span><span class="pln">



}


interface MathOperation {
int operation(int a, int b);
}


interface GreetingService {
void sayMessage(String message);
}


private int operate(int a, int b, MathOperation mathOperation) {
return mathOperation.operation(a, b);
}
}

使用javac编译器编译类，如下所示-

C:\JAVA>javac Java8Tester.java

现在运行Java8Tester，如下所示-

C:\JAVA>java Java8Tester

它应该生成以下输出-

10 + 5=15
10 - 5=5
10 x 5=50
10/5=2
Hello Mahesh
Hello Suresh

下面是在上面的例子中需要考虑的要点。

  • Lambda 表达式主要用于定义函数接口的内联实现，即仅具有单个方法的接口。在上面的示例中，无涯教程使用了各种类型的lambda表达式来定义MathOperation接口的操作方法，然后定义了GreetingService的sayMessage的实现。

  • Lambda表达式消除了匿名类，为Java提供了非常简单但函数强大的函数式编程能力。

Lambda作用域

使用lambda表达式，您可以引用任何final变量，如果第二次为变量赋值，Lambda表达式将引发编译错误。

使用您选择的任何编辑器创建以下Java程序，例如， C:\> JAVA.

Java8Tester.java

public class Java8Tester {

final static String salutation="Hello! ";


public static void main(String args[]) {
GreetingService greetService1=message ->
System.out.println(salutation + message);
greetService1.sayMessage("Mahesh");
}


interface GreetingService {
void sayMessage(String message);
}
}

使用javac编译器编译类，如下所示-

C:\JAVA>javac Java8Tester.java

现在运行Java8Tester，如下所示-

C:\JAVA>java Java8Tester

它应该生成以下输出-

Hello! Mahesh

参考链接

www.learnfk.com/java/java8-…

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