多线程

1. 并行与并发

并行：同一时刻，有多个指令在多个CPU上同时执行
并发：同一时刻，有多个指令在单个CPU上交替执行

2.进程和线程

进程：正在运行的软件

线程：进程中的单个顺序控制流，是一条执行路径

3. *****多线程的实现方式

3.1 继承Thread类的方式进行实现

public class MyThread extends Thread {@Overridepublic void run() {for (int i = 0; i < 100; i++) {System.out.println("线程开启"+i);}}public static void main(String[] args) {MyThread t1=new MyThread();MyThread t2=new MyThread();t1.start();t2.start();}
}

• 为什么要重写run()方法？
  多线程开启之后执行run()方法，run()是用来封装被线程执行的代码
• run()方法和start()方法的区别？
  run方法调用不开启线程，start开启线程

3.2 实现Runnable接口方式进行实现

public class MyRunnable implements Runnable{@Overridepublic void run() {for (int i = 0; i < 100; i++) {System.out.println("线程开启了"+i);}}public static void main(String[] args) {MyRunnable mr=new MyRunnable();Thread t1=new Thread(mr);t1.start();MyRunnable mrs=new MyRunnable();Thread t2=new Thread(mrs);t2.start();}
}

3.3 利用Callable和Future接口方式实现

public class MyCallable implements Callable<String> {@Overridepublic String call() throws Exception {for (int i = 0; i < 50; i++) {System.out.println("向女孩表白"+i);}return "答应";}public static void main(String[] args) throws ExecutionException, InterruptedException {MyCallable mt=new MyCallable();FutureTask<String> ft=new FutureTask<String>(mt);Thread t=new Thread(ft);t.start();String s = ft.get();System.out.println(s);}
}

get方法在线程开启之后调用
三种方式对比

3.4 设置获取线程名字

1. 获取线程名字

public class Mythread extends Thread {@Overridepublic void run() {for (int i = 0; i < 100; i++) {System.out.println(getName()+"****"+i);}}public static void main(String[] args) {Mythread mt=new Mythread();mt.start();Mythread ss=new Mythread();ss.start();}
}

2. 设置线程民资

• set形式

        Mythread mt=new Mythread();mt.start();mt.setName("线程1");Mythread ss=new Mythread();ss.start();ss.setName("线程2");

• 构造器形式

public class Mythread extends Thread {@Overridepublic void run() {for (int i = 0; i < 100; i++) {System.out.println(getName()+"****"+i);}}public Mythread(String name) {super(name);}public static void main(String[] args) {Mythread mt=new Mythread("线程1");mt.start();Mythread ss=new Mythread("线程2");ss.start();}
}

4.获得线程对象

在runnable中可以获取线程对象名字

public class MyRunnable implements Runnable {@Overridepublic void run() {for (int i = 0; i < 50; i++) {System.out.println(Thread.currentThread().getName()+"running"+i);}}public static void main(String[] args) {
//        MyRunnable myRunnable=new MyRunnable();
//        Thread thread=new Thread(myRunnable);
//        thread.setName("666");
//        thread.start();String name = Thread.currentThread().getName();System.out.println(name);}
}

5.线程休眠

Thread.sleep(3000);

 @Overridepublic void run() {for (int i = 0; i < 50; i++) {System.out.println(Thread.currentThread().getName()+"running"+i);try {Thread.sleep(3000);} catch (InterruptedException e) {e.printStackTrace();}}}

6.线程调度[线程的优先级]

public class MyCallable implements Callable<String> {@Overridepublic String call() throws Exception {for (int i = 0; i < 50; i++) {System.out.println(Thread.currentThread().getName()+"***"+i);}return "线程执行结束";}public static void main(String[] args) {MyCallable mc=new MyCallable();FutureTask<String> ft=new FutureTask<>(mc);Thread thread=new Thread(ft);thread.start();thread.setPriority(2);thread.setName("飞机");
//        System.out.println(thread.getPriority());MyCallable mc2=new MyCallable();FutureTask<String> ft2=new FutureTask<>(mc2);Thread t2=new Thread(ft2);t2.start();t2.setPriority(10);t2.setName("坦克");
//        System.out.println(t2.getPriority());}
}

7.后台线程/守护线程

普通线程结束 守护线程也随之结束

public class MyThread extends Thread {@Overridepublic void run() {for (int i = 0; i < 10; i++) {System.out.println(getName()+"****"+i);}}public MyThread(String name) {super(name);}public static void main(String[] args) {MyThread mt=new MyThread("女神");mt.start();MyThread2 t2=new MyThread2("备胎");t2.setDaemon(true);t2.start();}
}
public class MyThread2 extends Thread {@Overridepublic void run() {for (int i = 0; i < 100; i++) {System.out.println(getName()+"****"+i);}}public MyThread2(String name) {super(name);}
}