java 同步synchronized，lock(obj) ,读写锁

package num10;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

// java 读写锁
class M

{

    private static Map<Integer, String> map = new HashMap<Integer, String>();

    private static M m = new M(map);

    public static M getInstance()

    {

        return m;

    }

    private final java.util.concurrent.locks.ReadWriteLock lock = new ReentrantReadWriteLock();

    private final Lock r = lock.readLock();

    private final Lock w = lock.writeLock();

    public M(Map<Integer, String> map) {

        this.map = map;

    }

    public String put(Integer key, String value) {

        System.out.println("waiting put");

        w.lock();

        try {

            System.out.println("processing put");

            try {

                Thread.sleep(5000l);

            } catch (InterruptedException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            return map.put(key, value);

        } finally {
            System.out.println("put finish");
            w.unlock();

        }

    }

    public synchronized String put1(Integer key, String value) {

        System.out.println("waiting put1");

        try {

            System.out.println("processing put1");

            try {

                Thread.sleep(5000l);

            } catch (InterruptedException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            return map.put(key, value);

        } finally {
            System.out.println("put1 finish");
        }

    }

    public String get(Object key) {

        System.out.println("waiting get");

        r.lock();

        try {

            System.out.println("processing get");

            try {

                Thread.sleep(5000l);

            } catch (InterruptedException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            return map.get(key);

        } finally {
            System.out.println("get finish");
            r.unlock();

        }

    }

    public synchronized String get1(Object key) {

        System.out.println("waiting get1");

        try {

            System.out.println("processing get1");

            try {

                Thread.sleep(5000l);

            } catch (InterruptedException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            return map.get(key);

        } finally {
            System.out.println("get1 finish");

        }

    }

}

public class ReadWriteLock implements Runnable

{

    private int i;

    private boolean get;

    ReadWriteLock(int i, boolean get)

    {

        this.i = i;

        this.get = get;

    }

    public void run()

    {

        M m = M.getInstance();

        if (get)

        {

            m.get1(new Integer(1));

        }

        else

        {

            m.put1(new Integer(1), "1");

        }

    }

    public static void main(String[] args)

    {

        boolean getfirst = false;

        ReadWriteLock c = new ReadWriteLock(0, !getfirst);

        Thread t = new Thread(c);

        t.start();

        ReadWriteLock c2 = new ReadWriteLock(1, getfirst);

        Thread t2 = new Thread(c2);

        t2.start();

    }

}

运行结果如下：

waiting get1
processing get1
get1 finish
waiting put1
processing put1
put1 finish

可以看出synchronized 关键字相当于 lock(M.class), 是将整个对象锁住，为提高效率，可以使用读写锁

使用关键字的方法相当于如下的类所示，MethodA 和 MethodB 是同步方法

class SynchronizedTest {
    private static Object root = new Object();

    public void MethodA() {
        synchronized (root) {
            System.out.println("waiting MethodA");

            try {

                System.out.println("processing MethodA");

                try {

                    Thread.sleep(5000l);

                } catch (InterruptedException e) {

                    // TODO Auto-generated catch block

                    e.printStackTrace();

                }

            } finally {
                System.out.println("MethodA finish");

            }
        }
    }

    public void MethodB() {
        synchronized (root) {
            System.out.println("waiting MethodB");

            try {

                System.out.println("processing MethodB");

                try {

                    Thread.sleep(5000l);

                } catch (InterruptedException e) {

                    // TODO Auto-generated catch block

                    e.printStackTrace();

                }

            } finally {
                System.out.println("MethodA finish");

            }
        }
    }

    public void MethodC() {
        System.out.println("rocessing MethodC");
    }
}