/**
 * 線程任務(wù)
 * 用同步代碼塊解決同步方法的弊端
 * @author wuyoushan
 * @date 2017/1/23.
 */
public class Task {
    private String getData1;
    private String getData2;

    public void doLongTimeTask(){
        try {
            System.out.println("begin task");
            Thread.sleep(3000);
            String privateGetData1="長(zhǎng)時(shí)間處理任務(wù)后從遠(yuǎn)程返回的值1 threadName="+
                    Thread.currentThread().getName();
            String privateGetData2="長(zhǎng)時(shí)間處理任務(wù)后從遠(yuǎn)程返回的值2 threadName="+
                    Thread.currentThread().getName();
            synchronized (this){
                getData1=privateGetData1;
                getData2=privateGetData2;
            }
            System.out.println(getData1);
            System.out.println(getData2);
            System.out.println("end task");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

/**
 * 常量定義
 * 用同步代碼塊解決同步方法的弊端
 * @author wuyoushan
 * @date 2017/1/23.
 */
public class CommonUtils {
    public static long beginTime1;
    public static long endTime1;
    public static long beginTime2;
    public static long endTime2;
}


/**線程1
 * 用同步代碼塊解決同步方法的弊端
 * @author wuyoushan
 * @date 2017/1/23.
 */
public class MyThread1 extends Thread {
    private Task task;

    public MyThread1(Task task){
        this.task=task;
    }

    @Override
    public void run() {
        super.run();
        CommonUtils.beginTime1=System.currentTimeMillis();
        task.doLongTimeTask();
        CommonUtils.endTime1=System.currentTimeMillis();
    }
}

/**
 * 線程二
 * synchronized方法的弊端
 * @author wuyoushan
 * @date 2017/1/23.
 */
public class MyThread2 extends Thread {
    private Task task;

    public MyThread2(Task task){
        this.task=task;
    }

    @Override
    public void run() {
        super.run();
        CommonUtils.beginTime2=System.currentTimeMillis();
        task.doLongTimeTask();
        CommonUtils.endTime2=System.currentTimeMillis();
    }
}

/**運(yùn)行實(shí)例
 * 用同步代碼塊解決同步方法的弊端
 * @author wuyoushan
 * @date 2017/1/23.
 */
public class Run {
    public static void main(String[] args) {
        Task task=new Task();
        MyThread1 thread1=new MyThread1(task);
        thread1.start();
        MyThread2 thread2=new MyThread2(task);
        thread2.start();
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        long beginTime=CommonUtils.beginTime1;
        if (CommonUtils.beginTime2<CommonUtils.beginTime1){
            beginTime=CommonUtils.beginTime2;
        }
        long endTime=CommonUtils.endTime1;
        if (CommonUtils.endTime2>CommonUtils.endTime1){
            endTime=CommonUtils.endTime2;
        }
        System.out.println("耗時(shí):"+((endTime-beginTime)/1000));
    }
}

程序的運(yùn)行結(jié)果為：

begin task
begin task
長(zhǎng)時(shí)間處理任務(wù)后從遠(yuǎn)程返回的值1 threadName=Thread-1
長(zhǎng)時(shí)間處理任務(wù)后從遠(yuǎn)程返回的值2 threadName=Thread-0
end task
長(zhǎng)時(shí)間處理任務(wù)后從遠(yuǎn)程返回的值1 threadName=Thread-0
長(zhǎng)時(shí)間處理任務(wù)后從遠(yuǎn)程返回的值2 threadName=Thread-0
end task
耗時(shí):3

通過上面的實(shí)驗(yàn)可以得知协饲，當(dāng)一個(gè)線程訪問object的一個(gè)synchronized同步代碼塊時(shí)锣披，另一個(gè)線程仍然可以訪問改object對(duì)象中的非synchronized(this)同步代碼塊缘眶。

實(shí)驗(yàn)進(jìn)行到這里，雖然時(shí)間縮短谓谦，運(yùn)行效率加快酝碳，但同步synchronized代碼塊真的是同步的嗎？真的持有當(dāng)前調(diào)用對(duì)象的鎖嗎户辱？答案為是鸵钝，但必須用代碼的方式來進(jìn)行驗(yàn)證

摘選自 java多線程核心編程技術(shù)-2.2.3