java 死锁产生的四个必要条件：

• 1、互斥使用，即当资源被一个线程使用(占有)时，别的线程不能使用
• 2、不可抢占，资源请求者不能强制从资源占有者手中夺取资源，资源只能由资源占有者主动释放。
• 3、请求和保持，即当资源请求者在请求其他的资源的同时保持对原有资源的占有。
• 4、循环等待，即存在一个等待队列：P1占有P2的资源，P2占有P3的资源，P3占有P1的资源。这样就形成了一个等待环路。

package com.thread;import java.util.Date;import java.util.concurrent.TimeUnit;/** *  * @author zy * */public class LockTest {    public static void main(String[] args) {        String o1 = "o1";        String o2 = "o2";        String o3 = "o3";

　　   　　new Thread(new LockA(o1, o2), "t1").start();

　　　   　new Thread(new LockA(o2, o1), "t2").start();

　　　   　//new Thread(new LockA(o2, o3), "t2").start();

　　　   　// new Thread(new LockA(o3, o1), "t3").start();

}}class LockA implements Runnable {    private String o1;    private String o2;    public LockA(String o1, String o2) {        this.o1 = o1;        this.o2 = o2;    }    public void run() {        try {            String name = Thread.currentThread().getName();            System.out.println(new Date().toString() + " " + name + "   " + " acquiring lock on " + o1);            synchronized (o1) {                System.out.println(new Date().toString() + " " + name + "   " + " lock on " + o1);                TimeUnit.MILLISECONDS.sleep(300);                System.out.println(new Date().toString() + " " + name + "   " + " acquiring lock on " + o2);                synchronized (o2) {                    System.out.println(new Date().toString() + " " + name + "   " + " lock on " + o2);                    TimeUnit.MILLISECONDS.sleep(300);                }                System.out.println(new Date().toString() + " " + name + " released lock on " + o2);            }            System.out.println(new Date().toString() + " " + name + " released lock on " + o1);            System.out.println(new Date().toString() + " " + name + " finished execution.");        } catch (Exception e) {            e.printStackTrace();        }    }}

运行结果为：

Fri May 05 09:53:55 CST 2017 t2 acquiring lock on o2

Fri May 05 09:53:55 CST 2017 t2 lock on o2

Fri May 05 09:53:55 CST 2017 t1 acquiring lock on o1

Fri May 05 09:53:55 CST 2017 t1 lock on o1

Fri May 05 09:53:55 CST 2017 t1 acquiring lock on o2

Fri May 05 09:53:55 CST 2017 t2 acquiring lock on o1

这是两个线程死锁的时候，也可以让多个线程相互之间关联形成死锁，将注释去掉，再把第二个线程注释掉，就有三个资源相互关联的线程，运行结果:

Fri May 05 10:06:07 CST 2017 t3 acquiring lock on o3

Fri May 05 10:06:07 CST 2017 t3 lock on o3

Fri May 05 10:06:07 CST 2017 t1 acquiring lock on o1

Fri May 05 10:06:07 CST 2017 t1 lock on o1

Fri May 05 10:06:07 CST 2017 t2 acquiring lock on o2

Fri May 05 10:06:07 CST 2017 t2 lock on o2

Fri May 05 10:06:07 CST 2017 t3 acquiring lock on o1

Fri May 05 10:06:07 CST 2017 t2 acquiring lock on o3

Fri May 05 10:06:07 CST 2017 t1 acquiring lock on o2