多线程

简单讲解了关于多线程的一些应用：线程进程的概念区别，定义多线程，多线程之间的通信，线程的死锁，以及线程的优先级。此类问题在Java面试当中经常触及。

多线程.png

1.多线程的实践：

package Thread;
public class Live implements Runnable{
    public void run() {
        for(int i = 1;i<=6;i++){
            System.out.println("抠脚"+i+"次");
            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

package Thread;
public class Play extends Thread{
    public void run(){
        for(int i=1;i<=30;i++){
            System.out.println("who打单机：第"+i+"局，输了，玩的真菜！");
            try {
                Thread.sleep(50);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

package Thread;
/*
 * 多线程同时执行，有两种实现多线程的方法，一种是继承类，一种是实现接口。
 * 继承: 继承Thread的话，该子类应重写 Thread 类的 run 方法。接下来可以分配并启动该子类的实例
 * 实现接口：声明实现 Runnable 接口的类，该类然后实现 run 方法。
 * 然后可以分配该类的实例，在创建 Thread 时作为一个参数来传递并启动。
 * */
public class Thread_jichu { 
    
    public static void print(){
        for(int i=1;i<=50;i++){
            System.out.println("who看校花的贴身高手：第"+i+"集，看的挺嗨的！");
            try {
                Thread.sleep(50);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    
    public static void main(String[] args) {
        Thread t = new Play();  
        Live l = new Live();    
        Thread t1 = new Thread(l);
        t1.start();
        t.start();
        
        print();
    }
}

2.线程安全和同步：

package Thread;

public class Synchronized_tongbu {
    public static void main(String[] args) {
        BankAccount account = new BankAccount();
        Thread husband = new BankThread(account);
        Thread wife = new BankThread(account);
        husband.start();
        wife.start();
    }
}
class BankAccount{
    private double balance = 1000;
    public boolean depasit(double newAdd){
        if(newAdd <=0){
            return false;           
        }else{
            synchronized(this){//锁方法和锁局域代码
                System.out.println("当前余额为："+balance);
                try {
                    Thread.sleep(5);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                balance = balance + newAdd;
            }
            System.out.println("新的余额为：" + balance);
        }
        return true;    
    }
}
class BankThread extends Thread{
    private BankAccount bankAccount;
    public BankThread(BankAccount account){
        bankAccount = account;
    }
    public void run(){
        bankAccount.depasit(200);
    }
    
}

死锁

package Thread;
/*
 * 由于加锁，所以在取资源时某一方没有使用完不得进入该空间。
 * 
 * */
public class DeadLock {

    public static void main(String[] args) {
        Object object1 = new  Object();
        Object object2 = new  Object();
        Thread ta = new A(object1, object2);
        Thread tb = new B(object1, object2);
        ta.start();
        tb.start();
    }

}

class A extends Thread {
    Object object1;
    Object object2;

    public A(Object object1, Object object2) {
        this.object1 = object1;
        this.object2 = object2;
    }

    public void run() {
        synchronized (object1) {
            System.out.println("A取到了object1");
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized(object2){
                System.out.println("A拿到了object1和object2");
        }
        }
    }
}

class B extends Thread {
    public Object object1;
    public Object object2;

    public B(Object object1, Object object2) {
        this.object1 = object1;
        this.object2 = object2;
    }

    public void run() {
        synchronized (object2) {
            System.out.println("B取到了object1");
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized(object1){
                System.out.println("B拿到了object1和object2");
        }
        }
    }
}

如上代码会出现死锁，未能A B都未能取到所需，将B run方法中object2 object1调换即可。取得顺序相同很庆幸解决了问题。