在Java中，专门提供了锁对象，利用锁可以方便的实现资源的封锁，用来控制对竞争资源并发访问的控制；这些内容主要集中在java.util.concurrent.locks包下面，里面有三个重要的接口Condition、Lock、ReadWriteLock

   Condition将Object监视器方法（wait、notify和 notifyAll）分解成截然不同的对象，以便通过将这些对象与任意Lock实现组合使用，为每个对象提供多个等待 set（wait-set）；Lock实现提供了比使用synchronized方法和语句可获得的更广泛的锁定操作； ReadWriteLock维护了一对相关的锁定，一个用于只读操作，另一个用于写入操作

package unit_fifteen;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/** 
* Java线程：锁 
* 
*/ 
public class Test {
        public static void main(String[] args) {
                //创建并发访问的账户
                MyCount myCount = new MyCount("95599200901215522", 10000);
                //创建一个锁对象
                Lock lock = new ReentrantLock();
                //创建一个线程池
                ExecutorService pool = Executors.newCachedThreadPool(); 
                //创建一些并发访问用户，一个信用卡，存的存，取的取，好热闹啊
                User u1 = new User("张三", myCount, -4000, lock); 
                User u2 = new User("张三他爹", myCount, 6000, lock); 
                User u3 = new User("张三他弟", myCount, -8000, lock); 
                User u4 = new User("张三", myCount, 800, lock);
                //在线程池中执行各个用户的操作
                pool.execute(u1); 
                pool.execute(u2); 
                pool.execute(u3); 
                pool.execute(u4); 
                //关闭线程池
                pool.shutdown(); 
        } 
} 

/** 
* 信用卡的用户 
*/ 
class User implements Runnable { 
        private String name;                //用户名
        private MyCount myCount;        //所要操作的账户
        private int iocash;                //操作的金额，当然有正负之分了
        private Lock myLock;                //执行操作所需的锁对象

        User(String name, MyCount myCount, int iocash, Lock myLock) {
                this.name = name;
                this.myCount = myCount;
                this.iocash = iocash;
                this.myLock = myLock;
        } 

        public void run() {
                //获取锁
                myLock.lock(); 
                //执行现金业务
                System.out.println(name + "正在操作" + myCount +"账户，金额为" + iocash +"，当前金额为" + myCount.getCash());
                myCount.setCash(myCount.getCash() + iocash); 
                System.out.println(name + "操作" + myCount +"账户成功，金额为" + iocash +"，当前金额为" + myCount.getCash());
                //释放锁，否则别的线程没有机会执行了
                myLock.unlock(); 
        } 
} 

/** 
* 信用卡账户，可随意透支 
*/ 
class MyCount { 
        private String oid;        //账号
        private int cash;            //账户余额

        MyCount(String oid, int cash) {
                this.oid = oid;
                this.cash = cash;
        } 

        public String getOid() {
                return oid;
        } 

        public void setOid(String oid) {
                this.oid = oid;
        } 

        public int getCash() {
                return cash;
        } 

        public void setCash(int cash) {
                this.cash = cash;
        } 

        @Override 
        public String toString() {
                return"MyCount{" +
                                "oid='" + oid + '\'' +
                                ", cash=" + cash +
                                '}'; 
        } 
}

    在上文中提到了Lock接口以及对象，使用它，很优雅的控制了竞争资源的安全访问，但是这种锁不区分读写，称这种锁为普通锁。为了提高性能，Java提供了读写锁，在读的地方使用读锁，在写的地方使用写锁，灵活控制，在一定程度上提高了程序的执行效率；Java中读写锁有个接口java.util.concurrent.locks.ReadWriteLock，也有具体的实现ReentrantReadWriteLock

package unit_fifteen;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/** 
* Java线程：锁 
* 
*/ 
public class Test {
        public static void main(String[] args) {
                //创建并发访问的账户
                MyCount myCount = new MyCount("95599200901215522", 10000);
                //创建一个锁对象
                ReadWriteLock lock = new ReentrantReadWriteLock(false);
                //创建一个线程池
                ExecutorService pool = Executors.newFixedThreadPool(2); 
                //创建一些并发访问用户，一个信用卡，存的存，取的取，好热闹啊
                User u1 = new User("张三", myCount, -4000, lock, false); 
                User u2 = new User("张三他爹", myCount, 6000, lock, false); 
                User u3 = new User("张三他弟", myCount, -8000, lock, false); 
                User u4 = new User("张三", myCount, 800, lock,false); 
                User u5 = new User("张三他爹", myCount, 0, lock,true); 
                //在线程池中执行各个用户的操作
                pool.execute(u1); 
                pool.execute(u2); 
                pool.execute(u3); 
                pool.execute(u4); 
                pool.execute(u5); 
                //关闭线程池
                pool.shutdown(); 
        } 
} 

/** 
* 信用卡的用户 
*/ 
class User implements Runnable { 
        private String name;                //用户名
        private MyCount myCount;        //所要操作的账户
        private int iocash;                //操作的金额，当然有正负之分了
        private ReadWriteLock myLock;                //执行操作所需的锁对象
        private boolean ischeck;        //是否查询

        User(String name, MyCount myCount, int iocash, ReadWriteLock myLock,boolean ischeck) {
                this.name = name;
                this.myCount = myCount;
                this.iocash = iocash;
                this.myLock = myLock;
                this.ischeck = ischeck;
        } 

        public void run() {
                if (ischeck) {
                        //获取读锁
                        myLock.readLock().lock(); 
                        System.out.println("读：" + name +"正在查询" + myCount +"账户，当前金额为" + myCount.getCash());
                        //释放读锁
                        myLock.readLock().unlock(); 
                } else {
                        //获取写锁
                        myLock.writeLock().lock(); 
                        //执行现金业务
                        System.out.println("写：" + name +"正在操作" + myCount +"账户，金额为" + iocash +"，当前金额为" + myCount.getCash());
                        myCount.setCash(myCount.getCash() + iocash); 
                        System.out.println("写：" + name +"操作" + myCount +"账户成功，金额为" + iocash +"，当前金额为" + myCount.getCash());
                        //释放写锁
                        myLock.writeLock().unlock(); 
                } 
        } 
} 

/** 
* 信用卡账户，可随意透支 
*/ 
class MyCount { 
        private String oid;        //账号
        private int cash;            //账户余额

        MyCount(String oid, int cash) {
                this.oid = oid;
                this.cash = cash;
        } 

        public String getOid() {
                return oid;
        } 

        public void setOid(String oid) {
                this.oid = oid;
        } 

        public int getCash() {
                return cash;
        } 

        public void setCash(int cash) {
                this.cash = cash;
        } 

        @Override 
        public String toString() {
                return"MyCount{" +
                                "oid='" + oid + '\'' +
                                ", cash=" + cash +
                                '}'; 
        } 
}