本章节我们重点来讲讲 Java 8 中的 Runnable Lambda 表达式。众所周知,Java 8 中的 Runable 和 Callable 两个接口都添加了 @FunctionalInterface 注解,因此我们可以直接使用 Lambda 表达式来代替它们的 run() 和 call() 方法
Runnable 表达式
Java 8 开始支持 Lambda 表达式,所以,好像,一夜间,所有添加了 @FunctionalInterface 注解的方法都可以使用 Lambda 表达式来创建实例,Runnable 也不例外,我们可以直接使用一个 Lambda 表达式来创建它的实例
Runnable r = () -> System.out.println("Hello World!");
Thread th = new Thread(r);
th.start();
运行结果输出为 Hello World ,是不是很神奇,如果没有 Lambda 表达式,那么原来的代码可能如下
Runnable r = new Runnable() {
@Override
public void run() {
System.out.println("Hello World!");
}
};
Thread th = new Thread(r);
th.start();
如果我们的 Lambda 表达式需要多行代码,可以用一对打括号 {} 扩起来,就像下面这样
Runnable r = () -> {
Consumer<Book> style = (Book b) -> System.out.println("Book Id:"+b.getId() + ", Book Name:"+b.getName());
list.forEach(style);
};
如果Lambda 表达式需要使用到外部的参数,那么必须对参数添加 final 修饰符表示参数不可变更。
final List<Book> list = Arrays.asList(new Book(1, "Ramayan"), new Book(2, "Mahabharat"));
Runnable r = () -> {
Consumer<Book> style = (Book b) -> System.out.println("Book Id:"+b.getId() + ", Book Name:"+b.getName());
list.forEach(style);
};
我们还可以把 Runnable 表达式作为参数传递给 Thread 相关的方法
我们首先来定一个 Book.java 类
Book.java
package com.cxyroad.util.runnable;
public class Book {
public int id;
public String name;
public Book(int id, String name){
this.id = id;
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public void print(){
System.out.println("id:"+id + ", Name:"+name);
}
}
然后在一个 Runnable 中输出书籍的一些信息
Java8RunnableDemo.java
package com.cxyroad.util.runnable;
import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;
import com.concretepage.Book;
public class Java8RunnableDemo {
public static void main(String[] args) {
final List<Book> list = Arrays.asList(new Book(1, "Ramayan"), new Book(2, "Mahabharat"));
Runnable r1 = () -> list.forEach(Book::print);
Thread th1 = new Thread(r1);
th1.start();
Runnable r2 = () -> {
Consumer<Book> style = (Book b) -> System.out.println("Book Id:"+b.getId() + ", Book Name:"+b.getName());
list.forEach(style);
};
Thread th2 = new Thread(r2);
th2.start();
}
}
运行结果如下
id:1, Name:Ramayan
Book Id:1, Book Name:Ramayan
id:2, Name:Mahabharat
Book Id:2, Book Name:Mahabharat
同样的,我们还可以在 ExecutorService 中运行 Runnable
Java8RunnableDemoExecutor.java
package com.cxyroad.util.runnable;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.function.Consumer;
import com.concretepage.Book;
public class Java8RunnableDemoExecutor {
public static void main(String[] args) {
final List<Book> list = Arrays.asList(new Book(1, "Ramayan"), new Book(2, "Mahabharat"));
ExecutorService service = Executors.newFixedThreadPool(2);
Runnable r1 = () -> list.forEach(Book::print);
service.execute(r1);
Runnable r2 = () -> {
Consumer<Book> style = (Book b) -> System.out.println("Book Id:"+b.getId() + ", Book Name:"+b.getName());
list.forEach(style);
};
service.execute(r2);
}
}
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