Java 多线程

核心概念

通过继承Thread类实现

步骤
1.定义类继承Thread类
2.重写run方法
3.创建线程对象,调用start()方法

public class ThreadDemo1 extends Thread {
    @Override
    public void run() {
        for(int i=0;i<20;i++){
            System.out.println("正在第"+i+"次做该事情");
        }
    }

    public static void main(String[] args) {
        ThreadDemo1 threadDemo1=new ThreadDemo1();
        threadDemo1.start();//调用start方法才能实现多线程
        for(int i=0;i<=20;i++){
            System.out.println("主线程正在第"+i+"次做该事情");
        }
    }
}

运行出来会发现并不是线性顺序,会交替执行。

通过Runnable接口实现(推荐做法)

public class ThreadDemo2 implements Runnable {
    public void run() {
        for(int i=0;i<20;i++){
            System.out.println("正在第"+i+"次做该事情");
        }
    }

    public static void main(String[] args) {
        ThreadDemo2 threadDemo2=new ThreadDemo2();
        //需要创建一个线程对象
        //Thread thread=new Thread(threadDemo2);
        //thread.start();
        new Thread(threadDemo2).start();
        for(int i=0;i<=20;i++){
            System.out.println("主线程正在第"+i+"次做该事情");
        }
    }
}

简单例子：模拟龟兔赛跑

public class Race implements Runnable{
    private static String winner=null;
    public void run() {
        for(int i=0;i<=100;i++){
            if(Thread.currentThread().getName().equals("兔子") && i%10==0){
                //模拟兔子睡觉
                try {
                    Thread.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            if(gameOver(i)) break;
            System.out.println(Thread.currentThread().getName()+"跑了"+i+"米");
        }
    }
    private boolean gameOver(int step){
        if(winner!=null) return true;
        if(step>=100){
            winner=Thread.currentThread().getName();
            System.out.println("winner"+"is"+winner);
            return true;
        }
        else
            return false;
    }

    public static void main(String[] args) {
        Race race=new Race();
        new Thread(race,"兔子").start();
        new Thread(race,"乌龟").start();
    }
}

线程的安全性

//多个线程操作同一个对象
public class ThreadDemo3 implements Runnable{
    private int tickNums=10;
    public int sum=0;
    public void run() {
        try {
            Thread.sleep(200);//模拟延时
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        while(true){
            if(tickNums<=0) break;
            //Thread.currentThread().getName() 获取当前线程的名字
            System.out.println(Thread.currentThread().getName()+"拿到了第"+tickNums--+"票");
            sum++;
        }
    }

    public static void main(String[] args) {
        ThreadDemo3 threadDemo3=new ThreadDemo3();
        new Thread(threadDemo3,"小明").start();
        new Thread(threadDemo3,"小红").start();
        new Thread(threadDemo3,"小蓝").start();
    }
}

该程序有可能会出现问题。需要加🔒

Lambda表达式

概念:对于只包含唯一一个抽象方法的接口，那么就被定义为函数式接口
对函数式接口,我们可以通过lambda表达式来创建接口的对象
代码例子
传统写法:

interface InterfaceDemo{
    void fun();
}
public class LambdaDemo implements InterfaceDemo{
    public void fun() {
        System.out.println("实现接口--");
    }
}

class Run{
    public static void main(String[] args) {
        LambdaDemo lambdaDemo=new LambdaDemo();
        lambdaDemo.fun();
    }
}

使用匿名内部类

interface InterfaceDemo{
    void fun();
}
class Run{
    public static void main(String[] args) {
        //匿名内部类 必须借助接口或者父类
        InterfaceDemo demo = new InterfaceDemo() {
            public void fun() {
                System.out.println("实现接口--");
            }
        };
        demo.fun();
    }
}

Lambda

interface InterfaceDemo{
    void fun();
}
class Run{
    public static void main(String[] args) {
        //Lambda
        InterfaceDemo demo = ()->{
            System.out.println("Lambda的实现");
        };
        demo.fun();
    }
}