2022-08-07  阅读(540)
原文作者:简单教程 原文地址:https://www.twle.cn/

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 RunableCallable 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()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

Book.java

                package cn.twle.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 cn.twle.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 cn.twle.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);
                    }
                }

来源:https://www.twle.cn

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