两个线程交替打印1-100 结果只显示3个如图

public class A implements Runnable{
Demo demo;
public A(Demo demo){
this.demo=demo;
}

@Override
public void run() {
    while(demo.getNum()<100){
        demo.put();
    }

}

}

public class B implements Runnable {
Demo demo;

public B(Demo demo){
    this.demo=demo;
}

@Override
public void run() {
    if(demo.getNum()<100){
        demo.get();
    }

}

}

public class Demo {
private int num=1;

/**

• 打印偶数
  */
  public synchronized void put(){
  if(num%2==0){
  try {

          wait();
      } catch (InterruptedException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
      }
  
  }
  notify();
  System.out.println(Thread.currentThread().getName()+","+num);
  num++;
  

  }

/**

• 打印奇数
  */
  public synchronized void get(){
  if(num%2!=0){
  try {

          wait();
      } catch (InterruptedException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
      }
  
  }
  notify();
  System.out.println(Thread.currentThread().getName()+","+num);
  num++;
  

  }

public int getNum() {
return num;
}

public void setNum(int num) {
this.num = num;
}

}

public class Test {
public static void main(String[] args) {
Demo demo=new Demo();
A a=new A(demo);
B b=new B(demo);
Thread t1=new Thread(a);
Thread t2=new Thread(b);
t1.start();
t2.start();
}
}

结果为什么这样的：

B class 写的是 if

public class PrintNumber {
private int iterator;
private int limit;
private int start;
public PrintNumber(int limit,int start) {
this.limit=limit;
this.iterator=start;
this.start=start;
}

public synchronized void printSingle() {
    //如果是偶数的话则wait
    while ((iterator % 2) == 0 && iterator<=limit && start%2==0) {
        try {
            wait();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    while ((iterator % 2) != 0 && iterator<=limit) {
        System.out.println(Thread.currentThread().getName() + "---" + iterator++);
        notify();//唤醒打印偶数
        try {
            wait();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    notify();
}

public synchronized void printDouble() {
    //如果是奇数的话 则wait 
    while ((iterator % 2) != 0 && iterator<=limit &&  start%2!=0) {
        try {
            wait();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    while ((iterator % 2) == 0 && iterator<=limit) {
        System.out.println(Thread.currentThread().getName() + "---" + iterator++);
        notify();//唤醒打印奇数
        try {
            wait();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    notify();
}

}