发生死锁的原因通常是两个对象的锁相互等待造成的。 以下用一个实例来构造这样的情况：
package basic.e_deadlock;import org.apache.log4j.Logger;public class TestDeadLock { public static void main(String[] args) { DeadlockRisk dead = new DeadlockRisk(); MyThread t1 = new MyThread(dead, 1, 2, "线程1"); MyThread t2 = new MyThread(dead, 3, 4, "线程2"); MyThread t3 = new MyThread(dead, 5, 6, "线程3"); MyThread t4 = new MyThread(dead, 7, 8, "线程4"); t1.start(); t2.start(); t3.start(); t4.start(); }}class MyThread extends Thread { private DeadlockRisk dead; private int a, b; MyThread(DeadlockRisk dead, int a, int b, String threadName) { this.dead = dead; this.a = a; this.b = b; this.setName(threadName); } @Override public void run() { dead.read(); dead.write(a, b); }}class DeadlockRisk { private static Logger logger = Logger.getLogger(DeadlockRisk.class); private static class Resource { public int value; } private Resource resourceA = new Resource(); private Resource resourceB = new Resource(); public void read() { logger.debug("===========read begin==========="); synchronized (resourceA) { logger.debug("read():" + Thread.currentThread().getName() + "获取了resourceA 的锁！"); synchronized (resourceB) { logger.debug("read():" + Thread.currentThread().getName() + "获取了resourceB 的锁！"); } } logger.debug("===========read end============="); } public void write(int a, int b) { logger.debug("===========write begin==========="); synchronized (resourceB) { logger.debug("write():" + Thread.currentThread().getName() + "获取了resourceB 的锁！"); synchronized (resourceA) { logger.debug("write():" + Thread.currentThread().getName() + "获取了resourceA 的锁！"); resourceA.value = a; resourceB.value = b; } } logger.debug("===========write end============="); }} 运行结果： 0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========0 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========0 [线程4] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========0 [线程3] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - read():线程1获取了resourceA 的锁！0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - read():线程1获取了resourceB 的锁！0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========read end=============0 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - read():线程2获取了resourceA 的锁！0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========write being===========1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - read():线程2获取了resourceB 的锁！1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========read end=============1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========write being===========1 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - write():线程1获取了resourceB 的锁！1 [线程4] DEBUG basic.e_deadlock.DeadlockRisk - read():线程4获取了resourceA 的锁！注意：此时线程1在等待resourceB的资源，线程2在等待resourceA的资源。两个线程在相互等待，出现死锁。