java怎么同步_java怎么同步代码块

package sync.method;

class PrintCH {

public static void print(char c) {

for (int i = 0; i < 4; i++) {

System.out.print(c);

try {

Thread.sleep(1000);

} catch (InterruptedException e) {

e.printStackTrace();

}

}

}

}

public class SyncMassExample extends Thread {

public char c;

public /*static*/ PrintCH printCH = new PrintCH();    ///

public SyncMassExample(char c) {

this.c = c;

}

public void run() {

synchronized (printCH) {

PrintCH.print(c);

}

}

public static void main(String[] args) {

SyncMassExample s1 = new SyncMassExample('a');

SyncMassExample s2 = new SyncMassExample('b');

s1.start();

s2.start();

}

}

为什么同步代码块后的对象的应用得是静态的  就是我注释的那里  去掉static关键字 输出内容就乱了 交替输出a b