【Java】【Thread多线程】概述

2017-04-08 本文已影响67人 JerichoPH

多线程概述

通过子类继承开启多线程

public class Demo {
    public static void main(String[] args) throws IOException {
    MyThread myThread = new MyThread();
    myThread.start();
    
    for(int i = 0;i<1000;i++){
        System.out.print("b");
    }
}
}

class MyThread extends Thread {
    public void run() {
        for (int i = 0; i < 1000; i++) {
            System.out.print("a");
        }
    }
}

通过实现Runnable接口开启多线程

public class Demo {
    public static void main(String[] args) throws IOException {
        MyThread myThread = new MyThread();
        Thread t = new Thread(myThread);
        t.start();
        
        for (int i = 0; i < 1000; i++) {
            System.out.print("b");
        }
    }
}

class MyThread implements Runnable {
    @Override
    public void run() {
        for (int i = 0; i < 1000; i++) {
            System.out.print("a");
        }
    }
}

通过匿名内部类实现多线程

// 方法1
public static void main(String[] args) throws IOException {
    new Thread(){
        @Override
        public void run() {
            for(int i = 0;i<1000;i++){
                System.out.print("a");
            }
        }
    }.start();
    for(int i = 0;i<1000;i++){
        System.out.print("b");
    }
}
// 方法2
public static void main(String[] args) throws IOException {
    new Thread(new Runnable() {
        @Override
        public void run() {
            for (int i = 0; i < 1000; i++) {
                System.out.print("a");
            }
        }
    }) {
    }.start();
    for (int i = 0; i < 1000; i++) {
        System.out.print("b");
    }
}

设置和获取线程名称(setName&getName)

public class Demo {
    public static void main(String[] args) throws IOException {
        new Thread("subThread A") { // 通过构造方法修改名称
            @Override
            public void run() {
                for (int i = 0; i < 1000; i++) {
                    System.out.println(this.getName());
                }
            }
        }.start();
        
        new Thread() {
            @Override
            public void run() {
                this.setName("subThread B"); // 通过setName方法 修改线程名称
                for (int i = 0; i < 1000; i++) {
                    System.out.println(this.getName());
                }
            }
        }.start();
    }
}

获取当前线程对象(Thread.currentThread)

public class Demo {
    public static void main(String[] args) throws IOException {
        new Thread("subThread A") { // 通过构造方法修改名称
            @Override
            public void run() {
                for (int i = 0; i < 1000; i++) {
                    System.out.println(this.getName());
                }
            }
        }.start();
        
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 1000; i++) {
                    System.out.print(Thread.currentThread().getName()); // 通过Runnable方法实现的多线程，无法通过this获取Thread类对象，只能通过Thread.currentThread获取当前线程
                }
            }
        }) {
        }.start();
        
        // 通过Thread.currentThread方法获取和设置主线程属性
        Thread.currentThread().setName("我是主线程");
        System.out.println(Thread.currentThread().getName());
    }
}

线程休眠(sleep)

public class Demo {
    public static void main(String[] args) throws IOException {
        new Thread() {
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    System.out.println(new MyDatetime(System.currentTimeMillis()).getCn());
                    try { // 每次线程执行一次则休眠一秒
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }.start();
    }
}

守护线程(setDaemon)

public class Demo {
    public static void main(String[] args) throws IOException {
        Thread t1 = new Thread() { // 这里是守护线程
            @Override
            public void run() {
                for (int i = 0; i < 1000; i++) {
                    System.out.print("a"); // 执行1000次打印
                }
            }
        };
        
        Thread t2 = new Thread() {
            @Override
            public void run() {
                for (int i = 0; i < 5; i++) {
                    System.out.print("b"); // 执行5次打印
                }
            }
        };
        
        t1.setDaemon(true);
        
        t1.start();
        t2.start();
        // 结论：当正常线程结束后，守护线程跟随停止
    }
}

加入线程(join)

public class Demo {
    public static void main(String[] args) throws IOException {
        final Thread t1 = new Thread() { // 匿名内部类在使用其方法的时候需要使用final修饰
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    System.out.print("a");
                    try {
                        Thread.sleep(10);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
        Thread t2 = new Thread() {
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    if (i == 2) {
                        try {
                            t1.join();
                            Thread.sleep(10);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    System.out.print("b");
                }
            }
        };
        t1.start();
        t2.start();
        // 执行结果：abbaaaaaaaaabbbbbbb
    }
}

public class Demo {
    public static void main(String[] args) throws IOException {
        final Thread t1 = new Thread() { // 匿名内部类在使用其方法的时候需要使用final修饰
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    System.out.print("a");
                    try {
                        Thread.sleep(10);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
        Thread t2 = new Thread() {
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    if (i == 2) {
                        try {
                            t1.join(10); // 当b线程执行完成后，交还给a执行10毫秒，再次交替执行
                            Thread.sleep(10);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    System.out.print("b");
                }
            }
        };
        t1.start();
        t2.start();
        // 执行结果：abbaabbbbbbbbaaaaaaa
    }
}

同步代码块(synchronized)

public class Demo {
    public static void main(String[] args) throws IOException {
        final Person person = new Person();
        new Thread() {
            @Override
            public void run() {
                for (int i = 0; i <= 100; i++) {
                    person.printNum();
                    System.out.println();
                }
            }
        }.start();
        new Thread() {
            @Override
            public void run() {
                for (int i = 0; i < 100; i++) {
                    person.printLetter();
                    System.out.println();
                }
            }
        }.start();
    }
}

class Person {
    public void printNum() {
        // 强制程序执行时，执行该代码块完全执行后，再跳转其他线程。同步代码块
        synchronized (this) {
            System.out.print("1");
            System.out.print("2");
            System.out.print("3");
            System.out.print("4");
            System.out.print("5");
        }
    }
    
    public void printLetter() {
        synchronized (this) {
            System.out.print("a");
            System.out.print("b");
            System.out.print("c");
            System.out.print("d");
            System.out.print("e");
        }
    }
}

同步方法

public class Demo {
    public static void main(String[] args) throws IOException {
        final Person person = new Person();
        new Thread() {
            @Override
            public void run() {
                for (int i = 0; i <= 100; i++) {
                    person.printNum();
                    System.out.println();
                }
            }
        }.start();
        new Thread() {
            @Override
            public void run() {
                for (int i = 0; i < 100; i++) {
                    person.printLetter();
                    System.out.println();
                }
            }
        }.start();
    }
}

class Person {
// 同步方法
    public synchronized void printNum() {
        System.out.print("1");
        System.out.print("2");
        System.out.print("3");
        System.out.print("4");
        System.out.print("5");
    }
    
    public void printLetter() {
        synchronized (this) {
            System.out.print("a");
            System.out.print("b");
            System.out.print("c");
            System.out.print("d");
            System.out.print("e");
        }
    }

// 静态同步方法
    public static synchronized void printNum2() {
        System.out.print("1");
        System.out.print("2");
        System.out.print("3");
        System.out.print("4");
        System.out.print("5");
    }
    
    public static void printLetter2() {
        synchronized (Person.class) {
            System.out.print("a");
            System.out.print("b");
            System.out.print("c");
            System.out.print("d");
            System.out.print("e");
        }
    }
}

多线程安全

public class Demo {
    public static void main(String[] args) throws IOException {
        // 同时打开4个售票窗口进行售票
        new Ticket().start();
        new Ticket().start();
        new Ticket().start();
        new Ticket().start();
    }
}

// 售票窗口
class Ticket extends Thread {
    private static int ticket = 100;
    
    @Override
    public void run() {
        while (true) {
            synchronized (Ticket.class) { // 必须使用静态
                if (ticket <= 0) {
                    // 防止出现0号或负号票
                    break;
                }
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("第" + ticket-- + "张票");
            }
        }
    }
}

多线程安全（死锁）

public class Demo {

    private static String s1 = "《筷子左》";
    private static String s2 = "《筷子右》";
    
    public static void main(String[] args) throws IOException {
        // 使用者1
        new Thread("使用者1") {
            @Override
            public void run() {
                while(true){
                    synchronized (s1) {
                        System.out.println(this.getName() + "：拿到" + s1 + "等待" + s2);
                        synchronized (s2) {
                            System.out.println(this.getName() + "：拿到" + s2 + "开吃");
                        }
                    }
                }
            }
        }.start();
        
        // 使用者2
        new Thread("使用者2") {
            @Override
            public void run() {
                while(true){
                    synchronized (s2) {
                        System.out.println(this.getName() + "：拿到" + s2 + "等待" + s1);
                        synchronized (s1) {
                            System.out.println(this.getName() + "：拿到" + s1 + "开吃");
                        }
                    }
                }
            }
        }.start();
    }
}

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