当一个线程进入一个对象的一个synchronized方法后，其它线程是否可进入此对象的其它方法? ...

public class SyncTest {

/**
* @param args
*/
public static void main(String[] args) {
/*
* 当一个线程进入一个对象的一个synchronized方法后，其它线程是否可进入此对象的其它方法?
* 答：其他线程可以进入此对象的非同步方法，而不能进入其它的同步方法，
* 因为一个对象中的所有同步方法共用一个物件旗标（也就是对象本身）。
*
* 扩展：若新建另外一个对象，则可以实现两个同步方法同时执行。
*
*/
SyncTest st=new SyncTest();
Thread t=new Thread(st.new Sleep());
t.start(); //Thread-0
t=new Thread(st.new syncPrint());
t.start(); //Thread-1
t=new Thread(st.new Print());
t.start(); //Thread-2

SyncTest st2=new SyncTest();
t=new Thread(st2.new syncPrint());
t.start(); //Thread-3
}

private synchronized void sleep() throws InterruptedException{
Thread.currentThread().setName(Thread.currentThread().getName()+"@@sleep");
System.out.println(Thread.currentThread().getName()+": in ");
Thread.sleep(10000);
System.out.println(Thread.currentThread().getName()+": out ");
}

private synchronized void syncPrint() throws InterruptedException{
Thread.currentThread().setName(Thread.currentThread().getName()+"@@syncPrint");
System.out.println(Thread.currentThread().getName()+": in ");
for(int i=0;i<5;i++){
System.out.println(Thread.currentThread().getName()+": i="+i);
Thread.sleep(1000);
}
System.out.println(Thread.currentThread().getName()+": out ");
}

private void print() throws InterruptedException{
Thread.currentThread().setName(Thread.currentThread().getName()+"@@print");
System.out.println(Thread.currentThread().getName()+": in ");
for(int i=0;i<5;i++){
System.out.println(Thread.currentThread().getName()+": i="+i);
Thread.sleep(1000);
}
System.out.println(Thread.currentThread().getName()+": out ");
}

class Sleep implements Runnable{
public void run() {
// TODO Auto-generated method stub
try {
sleep();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

class Print implements Runnable{
public void run() {
// TODO Auto-generated method stub
try {
print();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

class syncPrint implements Runnable{
public void run() {
// TODO Auto-generated method stub
try {
syncPrint();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

运行结果：
Thread-0@@sleep: in
Thread-3@@syncPrint: in
Thread-3@@syncPrint: i=0
Thread-2@@print: in
Thread-2@@print: i=0
Thread-3@@syncPrint: i=1
Thread-2@@print: i=1
Thread-2@@print: i=2
Thread-3@@syncPrint: i=2
Thread-3@@syncPrint: i=3
Thread-2@@print: i=3
Thread-3@@syncPrint: i=4
Thread-2@@print: i=4
Thread-3@@syncPrint: out
Thread-2@@print: out
Thread-0@@sleep: out
Thread-1@@syncPrint: in
Thread-1@@syncPrint: i=0
Thread-1@@syncPrint: i=1
Thread-1@@syncPrint: i=2
Thread-1@@syncPrint: i=3
Thread-1@@syncPrint: i=4
Thread-1@@syncPrint: out