public class Student {
private Student(){}
private static Student s=new Student ();
public static Student getSingle() {
  return s;
}
String name;
int age;
boolean flag = false;
}
public class InputStudent implements Runnable {
Student s=Student.getSingle();
public InputStudent() {}
public InputStudent(Student s) {       //此处为什么还要写有参构造???
  this.s = s;
}
public void run() {
  int x = 0;
  while (true) {
   synchronized (s) {
    if(s.flag){
     try {
      s.wait();
     } catch (InterruptedException e) {
      e.printStackTrace();
     }
    }
    if (x % 2 == 0) {
     s.name = "林青霞";
     s.age = 20;
    } else {
     s.name = "刘德华";
     s.age = 40;
    }
    //唤醒打印线程
    s.flag = true;
    s.notify();
   }
   x++;
  }
}
}
public class OutputStudent implements Runnable {
Student s=Student.getSingle();
public OutputStudent() {
}
public OutputStudent(Student s) {            //此处为什么还要写有参构造???
  this.s = s;
}
public void run() {
  while (true) {
   synchronized (s) {
    if(!s.flag){
     try {
      s.wait();
     } catch (InterruptedException e) {
      e.printStackTrace();
     }
    }   
    System.out.println(s.name + "***" + s.age);
    s.flag = false;
    s.notify();
   }
  }
}
}
public class ResourceTest {
public static void main(String[] args) {
  Student s = Student.getSingle();
  
  InputStudent is = new InputStudent(s);
  OutputStudent os = new OutputStudent(s);
  
  Thread t1 = new Thread(is);
  Thread t2 = new Thread(os);
  
  t1.start();
  t2.start();
}
}
在InputStudent和OutputStudent类中为什么还要定义有参构造啊?不是已经调用Student s=Student.getSingle();了吗?
我把那两个构造方法去掉后照样也可以运行.那它们的作用是什么?很是费解!请各位大侠帮帮忙,小弟在此谢过.

其实没有什么作用,你传了也是指的Student同一个对象，不传也是指向了Student同一个对象，这是上面单例（饿汉式）造成的结果，你写了感觉代码很繁琐。不如不写。

哈哈！个人的小见解，不用谢。广彬兄很威武啊！