Java进阶知识查漏补缺05

Java线程死锁：

package com.cjf.ThreadAppl;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * Author: Everything
 * Date: 2020-07-01
 * Time: 20:48
 */
//死锁问题
public class DeadLockTest {

    public static void main(String[] args) {

        StringBuffer s1 = new StringBuffer();
        StringBuffer s2 = new StringBuffer();

        new Thread(){
            @Override
            public void run() {
                synchronized (s1){
                    s1.append("a");
                    s2.append("1");

                    try {
                        sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    synchronized (s2){
                        s1.append("b");
                        s2.append("2");

                        System.out.println(s1);
                        System.out.println(s2);
                    }
                }
            }
        }.start();


        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (s2) {
                    s1.append("c");
                    s2.append("3");

                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                    synchronized (s1) {
                        s1.append("d");
                        s2.append("4");

                        System.out.println(s1);
                        System.out.println(s2);
                    }
                }
            }
        }).start();
    }
}

解决Java线程死锁，改进懒汉式单例模式

package com.cjf.ThreadAppl;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * Author: Everything
 * Date: 2020-07-01
 * Time: 20:23
 */

//改进懒汉式单例模式
public class SingletonSenior {

}

class Bank{
    private Bank(){

    }

    private static Bank instance = null;

    public static  Bank getInstance() {
        //这种方式，会让后面的进程一直重复无用的判断工作，当前已经不能创建新的对象，直接进入return效率会更高
//        synchronized (Bank.class) {
//            if (instance == null) {
//                instance = new Bank();
//            }
//            return instance;
//        }
        //下面这种效率高
        if(instance == null){
            synchronized (Bank.class) {
            if (instance == null) {
                instance = new Bank();
            }
        }
        }
        return instance;
    }
}

使用Lock锁解决线程安全问题

package com.cjf.ThreadAppl;

import sun.security.krb5.internal.Ticket;

import javax.swing.plaf.SliderUI;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * Author: Everything
 * Date: 2020-07-01
 * Time: 21:12
 */

//jdk5以后加入
//方法三：使用Lock锁解决线程安全问题
class Window implements Runnable{
    private int ticket=100;

    //实例化一个ReentrantLock锁
    private ReentrantLock lock = new ReentrantLock();

    @Override
    public void run() {
        while (true){
            try {
                //调用锁定方法lock
                lock.lock();
                if(ticket > 0){
                    try {
                        Thread.sleep(10);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    ticket--;
                    System.out.println(Thread.currentThread().getName()+"售出票，余票"+ticket+"张");
                }else {
                    break;
                }
            }finally {
                //调用解锁方法
                lock.unlock();
            }
        }
    }
}




public class LockTest {
    public static void main(String[] args) {
        Window window1 = new Window();
        Thread thread1 = new Thread(window1);
        Thread thread2 = new Thread(window1);
        Thread thread3 = new Thread(window1);
        thread1.setName("窗口一");
        thread2.setName("窗口二");
        thread3.setName("窗口三");
        thread1.start();
        thread2.start();
        thread3.start();
    }
}