Question

一道关于JAVA的题目，急求答案。

(1)用继承Thread类方法创建线程MyThread类，该线程的功能是输出26个英文字母(大写，不换行)，每输出一个字母后，休眠时间是500—2000毫秒的随机数；
(2)用实现Runnable接口方法创建线程MyRunnalbe类，该线程的功能是输出26个英文字母(小写，不换行)，每输出一个字母后，休眠时间是500—2000毫秒的随机数；
(3)在主类中分别创建这两个类的对象t1、t2，并启动。
(提示：500—2000的随机数表示：500+(2000-5000)*Math.random() )
附上我自己的答案：
class MyThread extends Thread{
public void run(){
char ch;
try{
for (ch='A';ch<='Z';ch++){
System.out.print(ch+" ");
sleep((int)(500+(2000-5000)*Math.random()));
}
}catch (InterruptedException e){
return;
}
}
}

class MyRunnable implements Runnable {
public void run(){
char ch;
try{
for (ch='a';ch<='z';ch++){
System.out.print(ch+" ");
Thread.sleep((int)(500+(2000-5000)*Math.random()));
}
}catch (InterruptedException e){
return;
}
}
}

public class ThreadTest {
public static void main(String args[]) {
MyThread t1 = new MyThread();
MyRunnable r = new MyRunnable();
Thread t2 = new Thread(r);
t1.start();
t2.start();
}
} 请问为什么无法编译？

Answer 1

那是因为你随机数产生的是负数，你说让一个线程休眠时间为负数，那怎么可能，正确如下：class MyThread extends Thread{
public void run(){
char ch;
try{
for (ch='A';ch<='Z';ch++){
System.out.print(ch+" ");
Thread.sleep((int)(500+(2000-500)*Math.random()));
}
}catch (InterruptedException e){
return;
}
}
}

class MyRunnable implements Runnable {
public void run(){
char ch;
try{
for (ch='a';ch<='z';ch++){
System.out.print(ch+" ");
Thread.sleep((int)(500+(2000-500)*Math.random()));
}
}catch (InterruptedException e){
return;
}
}
}

public class ThreadTest {
public static void main(String args[]) {
MyThread t1 = new MyThread();
MyRunnable r = new MyRunnable();
Thread t2 = new Thread(r);
t1.run();
t2.start();
}
}
如果是t1.start()那么将会交替产生大小字母，而t1.run()则会产生出所有大写字母后，再差生所有小写字母

Answer 2

楼上说的对啊，不过该这样改，把500+(2000-5000)*Math.random() 改成500+15000*Math.random()
class MyThread extends Thread{
public void run(){
char ch;
try{
for (ch='A';ch<='Z';ch++){
System.out.print(ch+" ");
sleep((int)(500+15000*Math.random()));
}
}catch (InterruptedException e){
return;
}
}
}

class MyRunnable implements Runnable {
public void run(){
char ch;
try{
for (ch='a';ch<='z';ch++){
System.out.print(ch+" ");
Thread.sleep((int)(500+15000*Math.random()));
}
}catch (InterruptedException e){
return;
}
}
}

public class ThreadTest {
public static void main(String args[]) {
MyThread t1 = new MyThread();
MyRunnable r = new MyRunnable();
Thread t2 = new Thread(r);
t1.start();
t2.start();
}
}