Question

运用java编写一个继承thread类的类，然后实例化两个线程，并分别启动它们，并输出结果。

请大家帮忙，很急，谢谢

Answer 1

public class TestThread extends Thread {
public static void main(String[] args) {
TestThread p = new TestThread();
Thread t1 = new Thread(p);
Thread t2 = new Thread(p);
t1.start();
t2.start();
System.out.println(t1.activeCount());
System.out.println(t2.activeCount());
}
}

activeCount()方法返回的是当前线程的线程组中活动线程的数目。结果是3，为什么是3呢？因为程序执行main方法时也相当于启动了一个线程。还有就是一定要在线程启动后调用这个方法并打印，不然编译不了，假如程序比较长，放在最后的话结果可能是1，因为那时你的线程已经死亡了、结束了，剩下的就是main这一个线程。

Answer 2

public class E2 {
public static void main(String[] args) {
People teacher, student;
ComputerSum sum = new ComputerSum();
teacher = new People("老师", 200, sum);
student = new People("学生", 200, sum);
teacher.start();
student.start();
}
}

class ComputerSum {
int sum;

public void setSum(int n) {
sum = n;
}

public int getSum() {
return sum;
}
}

class People extends Thread {
int timeLength;// 线程的休眠时间长度
ComputerSum sum;

People(String s, int timeLength, ComputerSum sum) {
setName(s);// 调用Thread类的方法setName为线程起名字
this.timeLength = timeLength;
this.sum = sum;
}

public void run() {
for (int i = 1; i <= 5; i++) {
int m = sum.getSum();
sum.setSum(m + 1);
System.out.println("我是" + getName() + ", 现在的和:" + sum.getSum());
try {
sleep(timeLength);
} catch (InterruptedException e) {
}
}
}
}