Java多线程输出打印不正确，具体见下

[HJMing123]

最近在看毕向东的视频多线程的示例程序，发现自己这个程序总是打不对。
一个线程负责存入姓名与性别，另一个线程负责打印。要求是存入一个，打印一个。

class Res 
{
	String name;
	String gender;
	boolean pos = false;
}

class Input implements Runnable             //存入性别，性别
{
	private Res r;
	Input(Res r)
	{
		this.r=r;
	}

	public void run()              //重写run方法，存入
	{	
		int flag=0;
		for(int i=0;i<100;i++ )
		{
			
			synchronized(r)
			{
				if(r.pos)
				{
					try {
						r.wait();
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}	

				if(flag==0)
				{
					r.name="Jack";
					r.gender="male";
				}
				else if(flag==1)
				{
					r.name="lily";
					r.gender="female";
				}
					flag=(flag+1)%2;
					r.pos=true;
					r.notify();					

						
			}
		}
	}
	
}
class Output implements Runnable       //打印姓名，性别
{
	private Res r;
	Output(Res r)
	{
		this.r=r;
	}
	public void run()             //打印出姓名，性别
	{
		synchronized(r)
		{
			
			for(int i =0;i<100;i++)
			{
				if(r.pos==true)
				{
					System.out.println(r.name+".."+r.gender+".."+i);
					r.pos=false;
					r.notify();
				}
				else                //如果把这行改为 if(r.pos==false)结果正确
				{
					try {
						r.wait();
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}
	}	
}
public class TTT 
{
	public static void main(String[]args)
	{
		Res s = new Res();
		Input i = new Input(s);
		Output o =new Output(s);
		Thread t1 =new Thread(i);
		Thread t2 =new Thread(o);
		t1.start();
		t2.start();	
	}
}

打印结果为：
Jack..male..0
lily..female..2
Jack..male..4
lily..female..6
Jack..male..8
lily..female..10
Jack..male..12
lily..female..14
Jack..male..16
lily..female..18
Jack..male..20
lily..female..22
Jack..male..24
lily..female..26
Jack..male..28
lily..female..30
Jack..male..32
lily..female..34
Jack..male..36
lily..female..38
Jack..male..40
lily..female..42
Jack..male..44
lily..female..46
Jack..male..48
lily..female..50
Jack..male..52
lily..female..54
Jack..male..56
lily..female..58
Jack..male..60
lily..female..62
Jack..male..64
lily..female..66
Jack..male..68
lily..female..70
Jack..male..72
lily..female..74
Jack..male..76
lily..female..78
Jack..male..80
lily..female..82
Jack..male..84
lily..female..86
Jack..male..88
lily..female..90
Jack..male..92
lily..female..94
Jack..male..96
lily..female..98
而我想要的结果如下：
Jack..male..0
lily..female..1
Jack..male..2
lily..female..3
Jack..male..4
lily..female..5
Jack..male..6
lily..female..7
Jack..male..8
lily..female..9
Jack..male..10
lily..female..11
Jack..male..12
lily..female..13
Jack..male..14
lily..female..15
Jack..male..16
lily..female..17
Jack..male..18
lily..female..19
Jack..male..20
lily..female..21
Jack..male..22
lily..female..23
Jack..male..24
lily..female..25
Jack..male..26
lily..female..27
Jack..male..28
lily..female..29
Jack..male..30
lily..female..31
Jack..male..32
lily..female..33
Jack..male..34
lily..female..35
Jack..male..36
lily..female..37
Jack..male..38
lily..female..39
Jack..male..40
lily..female..41
Jack..male..42
lily..female..43
Jack..male..44
lily..female..45
Jack..male..46
lily..female..47
Jack..male..48
lily..female..49
Jack..male..50
lily..female..51
Jack..male..52
lily..female..53
Jack..male..54
lily..female..55
Jack..male..56
lily..female..57
Jack..male..58
lily..female..59
Jack..male..60
lily..female..61
Jack..male..62
lily..female..63
Jack..male..64
lily..female..65
Jack..male..66
lily..female..67
Jack..male..68
lily..female..69
Jack..male..70
lily..female..71
Jack..male..72
lily..female..73
Jack..male..74
lily..female..75
Jack..male..76
lily..female..77
Jack..male..78
lily..female..79
Jack..male..80
lily..female..81
Jack..male..82
lily..female..83
Jack..male..84
lily..female..85
Jack..male..86
lily..female..87
Jack..male..88
lily..female..89
Jack..male..90
lily..female..91
Jack..male..92
lily..female..93
Jack..male..94
lily..female..95
Jack..male..96
lily..female..97
Jack..male..98
lily..female..99

如我所述：只要把else改为if(r.pos==false)即可，但这两者不是一样的吗？难道是我忽略了什么吗？

[HJMing123]

不好意思，我的意思是 如果是else的话，程序的运行结果是第一个，如果是if(r.pos==false)的第二个，我想知道两者的区别在哪里？

[HJMing123]

引用 1 楼 pany1209 的回复:

两者肯定不一样啊，如果没有else或者if(r.pos==false)，r.notify()后会执行r.wait(),如果有就不会执行

不好意思，我的意思是 如果是else的话，程序的运行结果是第一个，如果是if(r.pos==false)的第二个，我想知道两者的区别在哪里？

[李德胜1995]

两者肯定不一样啊，如果没有else或者if(r.pos==false)，r.notify()后会执行r.wait(),如果有就不会执行