1、对于synchronized方法和synchronized块，一个线程访问时，其他线程可以访问此类的非synchronized方法或块，不能访问其他带synchronized的方法或块。

举例如下：

synchronized块：

public class Thread2 {

public void m4t1() {
synchronized (this) {
int i = 5;
while (i-- > 0) {
System.out.println(Thread.currentThread().getName() + " : " + i);
try {
Thread.sleep(2000);
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
}
}

public void m4t2() {
synchronized (this) {
int i = 5;
while (i-- > 0) {
System.out.println(Thread.currentThread().getName() + " : " + i);
try {
Thread.sleep(2000);
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
}
}

public static void main(String[] args) {
final Thread2 myt2 = new Thread2();
Thread t1 = new Thread(new Runnable() {
public void run() {
myt2.m4t1();
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
public void run() {
myt2.m4t2();
}
}, "t2");
t1.start();
t2.start();
}
}

synchronized方法：

public class Thread3 {

public synchronized void m4t1() {

int i = 5;
while (i-- > 0) {
System.out.println(Thread.currentThread().getName() + " : " + i);
try {
Thread.sleep(2000);
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}

}

public synchronized void m4t2() {

int i = 5;
while (i-- > 0) {
System.out.println(Thread.currentThread().getName() + " : " + i);
try {
Thread.sleep(2000);
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}

}

public static void main(String[] args) {
final Thread3 myt2 = new Thread3();
Thread t1 = new Thread(new Runnable() {
public void run() {
myt2.m4t1();
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
public void run() {
myt2.m4t2();
}
}, "t2");
t1.start();
t2.start();
}

java关键字synchronized