父进程等待所有子进程结束后再结束

这是个挺有趣的程序，我写了个例子同步了10个子线程，可以参考下：
public class Test {
static Test test = null;
static int childNum = 0;
synchronized static void decSem(){
childNum--;
if(childNum == 0){
synchronized(test){
test.notify();
}
}
}

Test(){
test = this;
}

void connectDB() throws InterruptedException{
synchronized(this){
childNum = 10;
new TestThread().start();
new TestThread().start();
new TestThread().start();
new TestThread().start();
new TestThread().start();
new TestThread().start();
new TestThread().start();
new TestThread().start();
new TestThread().start();
new TestThread().start();
wait();
}
}
public static void main(String[] args) throws InterruptedException {
System.out.println("Start...");
Test test = new Test();
test.connectDB();
System.out.println("End.");
}
}

class TestThread extends Thread{
public void run() {
super.run();
System.out.println("child thread");
Test.decSem();
}
}