使用synchronized和Lock对象获取对象锁
在并发环境下，解决共享资源冲突问题时，可以考虑使用锁机制。
1.对象的锁
所有对象都自动含有单一的锁。
JVM负责跟踪对象被加锁的次数。如果一个对象被解锁，其计数变为0。在任务（线程）第一次给对象加锁的时候，计数变为1。每当这个相同的任务（线程）在此对象上获得锁时，计数会递增。
只有首先获得锁的任务（线程）才能继续获取该对象上的多个锁。
每当任务离开一个synchronized方法，计数递减，当计数为0的时候，锁被完全释放，此时别的任务就可以使用此资源。
2.synchronized同步块
当使用同步块时，如果方法下的同步块都同步到一个对象上的锁，则所有的任务（线程）只能互斥的进入这些同步块。
Resource1.java演示了三个线程（包括main线程）试图进入某个类的三个不同的方法的同步块中，虽然这些同步块处在不同的方法中，但由于是同步到同一个对象（当前对象 synchronized (this)），所以对它们的方法依然是互斥的。
package cn.java.loak;import java.util.concurrent.TimeUnit;public class Resource1 {public void f(){System.out.println(Thread.currentThread().getName()+":not synchronized in f()");synchronized(this){for(int i=0;i<5; i++){System.out.println(Thread.currentThread().getName()+":synchronized in f()");try{TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e){e.printStackTrace();}}}}public void g(){System.out.println(Thread.currentThread().getName()+":not synchronized in g()");synchronized(this){for(int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+":synchronized in g()");try{TimeUnit.SECONDS.sleep(3);}catch (InterruptedException e){e.printStackTrace();}}}}public void h(){System.out.println(Thread.currentThread().getName()+":not synchronized in h()");synchronized(this){for(int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+":synchronized in h()");try{TimeUnit.SECONDS.sleep(3);} catch(InterruptedException e){e.printStackTrace();}}}}public static void main(String [] args){final Resource1 rs=new Resource1();new Thread(){public void run(){rs.f();}}.start();new Thread(){public void run(){rs.g();}}.start();rs.h();}}package cn.java.loak;import java.util.concurrent.TimeUnit;public class Resource2 {private Object syncObject1=new Object();private Object syncObject2=new Object();public void f(){System.out.println(Thread.currentThread().getName()+":not synchronized in f()");synchronized(this){for(int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+":synchronized in f()");try{TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e){e.printStackTrace();}}}}public void g(){System.out.println(Thread.currentThread().getName()+":not synchronized in g()");synchronized (syncObject1){for(int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+":synchronized in g()");try{TimeUnit.SECONDS.sleep(3);} catch(InterruptedException e){e.printStackTrace();}}}}public void h(){System.out.println(Thread.currentThread().getName()+":not synchronized in h()");synchronized(syncObject2){for(int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+":synchronized in h()");try{TimeUnit.SECONDS.sleep(3);} catch(InterruptedException e){e.printStackTrace();}}}}/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubfinal Resource2 rs=new Resource2();new Thread(){public void run(){rs.f();}}.start();new Thread(){public void run(){rs.g();}}.start();rs.h();}}package cn.java.loak;import java.util.concurrent.TimeUnit;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class Resource3 {private Lock lock = new ReentrantLock();public void f(){System.out.println(Thread.currentThread().getName()+":not synchronized in f()");lock.lock();try{for (int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+"synchronized in f()");try{TimeUnit.SECONDS.sleep(3);}catch(InterruptedException e){e.printStackTrace();}}}finally{lock.unlock();}}public void g(){System.out.println(Thread.currentThread().getName()+":not synchronized in g()");lock.lock();try{for (int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+"synchronized in g()");try{TimeUnit.SECONDS.sleep(3);}catch(InterruptedException e){e.printStackTrace();}}}finally{lock.unlock();}}public void h(){System.out.println(Thread.currentThread().getName()+":not synchronized in h()");lock.lock();try{for (int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+"synchronized in h()");try{TimeUnit.SECONDS.sleep(3);}catch(InterruptedException e){e.printStackTrace();}}}finally{lock.unlock();}}public static void main(String[] args){final Resource3 rs=new Resource3();new Thread(){public void run(){rs.f();}}.start();new Thread(){public void run(){rs.g();}}.start();rs.h();}}package cn.java.loak;import java.util.concurrent.TimeUnit;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class Resource4 {private Lock lock1=new ReentrantLock();private Lock lock2=new ReentrantLock();private Lock lock3=new ReentrantLock();public void f(){System.out.println(Thread.currentThread().getName()+":not synchronized in f()");lock1.lock();try{for(int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+":synchronized in f()");try{TimeUnit.SECONDS.sleep(3);}catch(InterruptedException e){e.printStackTrace();}}}finally{lock1.unlock();}}public void g(){System.out.println(Thread.currentThread().getName()+":not synchronized in g()");lock2.lock();try{for(int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+":synchronized in g()");try{TimeUnit.SECONDS.sleep(3);}catch(InterruptedException e){e.printStackTrace();}}}finally{lock2.unlock();}}public void h(){System.out.println(Thread.currentThread().getName()+":not synchronized in h()");lock3.lock();try{for(int i=0;i<5;i++){System.out.println(Thread.currentThread().getName()+":synchronized in h()");try{TimeUnit.SECONDS.sleep(3);}catch(InterruptedException e){e.printStackTrace();}}}finally{lock3.unlock();}}public static void main(String[] args){final Resource4 rs=new Resource4();new Thread(){public void run(){rs.f();}}.start();new Thread(){public void run(){rs.g();}}.start();rs.h();}}