public class HelloWorld{
public static void main(String[] args){
int num = 999;
int count = 0;
for(;;){
count++;
num = num / 10;
while(num>=0)
System.out.println("它是个"+count+"位的数！");
}
}
}因为你无限循环了，
改为
num = num / 10;if(num<=0) System.out.println("它是个"+count+"位的数！");
break;
public static void (){
System.out.println("你吗的大鸡腿，骗子");