为什么加了同步块，还是出现了负的票数呢

//1.创建一个实例类实现Runnable接口，现象接口中的run方法，将要执行的代码放入到方法中

class thread2 implements Runnable{

//假设有一百张票在四个窗口出售

private int i=100;

@Override

public void run() {

// TODO Auto-generated method stub

Object obj=new Object();

while(true) {

synchronized(obj){

if(i>0) {

try {

Thread.sleep(10);

} catch (InterruptedException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

System.out.println(Thread.currentThread()+"+"+i--);

}elsebreak; } }

}

}

//通过实现Runnable接口的方式创建线程

public class 实现runnable接口 {

public int i=100;

publicstaticvoidmain(String[] args){// TODO Auto-generated method stub//2.创建一个实现类对象thread2 th=newthread2();//3.创建四个Thread对象，将th作为参数传入Thread Th1=newThread(th); Thread Th2=newThread(th); Thread Th3=newThread(th); Thread Th4=newThread(th);//4.调用start方法，开启线程，调用实现接口子类中的run方法Th1.start(); Th2.start(); Th3.start(); Th4.start(); }

}

输出结果：

Thread[Thread-0,5,main]+100

Thread[Thread-3,5,main]+99

Thread[Thread-2,5,main]+98

Thread[Thread-1,5,main]+97

Thread[Thread-0,5,main]+96

Thread[Thread-2,5,main]+95

Thread[Thread-1,5,main]+94

Thread[Thread-3,5,main]+94

Thread[Thread-0,5,main]+93

Thread[Thread-2,5,main]+92

Thread[Thread-1,5,main]+91

Thread[Thread-3,5,main]+92

Thread[Thread-0,5,main]+91

Thread[Thread-1,5,main]+90

Thread[Thread-3,5,main]+89

Thread[Thread-2,5,main]+90

Thread[Thread-0,5,main]+88

Thread[Thread-3,5,main]+87

Thread[Thread-1,5,main]+86

Thread[Thread-2,5,main]+86

Thread[Thread-0,5,main]+85

Thread[Thread-3,5,main]+84

Thread[Thread-1,5,main]+83

Thread[Thread-2,5,main]+82

Thread[Thread-0,5,main]+81

Thread[Thread-3,5,main]+80

Thread[Thread-1,5,main]+79

Thread[Thread-2,5,main]+78

Thread[Thread-0,5,main]+77

Thread[Thread-3,5,main]+76

Thread[Thread-1,5,main]+75

Thread[Thread-2,5,main]+74

Thread[Thread-0,5,main]+73

Thread[Thread-3,5,main]+72

Thread[Thread-1,5,main]+71

Thread[Thread-2,5,main]+70

Thread[Thread-3,5,main]+69

Thread[Thread-1,5,main]+68

Thread[Thread-0,5,main]+67

Thread[Thread-2,5,main]+66

Thread[Thread-1,5,main]+65

Thread[Thread-2,5,main]+63

Thread[Thread-3,5,main]+64

Thread[Thread-1,5,main]+62

Thread[Thread-0,5,main]+61

Thread[Thread-2,5,main]+60

Thread[Thread-3,5,main]+59

Thread[Thread-1,5,main]+58

Thread[Thread-0,5,main]+57

Thread[Thread-2,5,main]+56

Thread[Thread-3,5,main]+55

Thread[Thread-1,5,main]+54

Thread[Thread-0,5,main]+53

Thread[Thread-2,5,main]+52

Thread[Thread-1,5,main]+51

Thread[Thread-3,5,main]+50

Thread[Thread-0,5,main]+49

Thread[Thread-2,5,main]+48

Thread[Thread-3,5,main]+47

Thread[Thread-1,5,main]+46

Thread[Thread-0,5,main]+45

Thread[Thread-2,5,main]+44

Thread[Thread-3,5,main]+43

Thread[Thread-1,5,main]+42

Thread[Thread-0,5,main]+41

Thread[Thread-2,5,main]+40

Thread[Thread-3,5,main]+39

Thread[Thread-1,5,main]+38

Thread[Thread-0,5,main]+37

Thread[Thread-2,5,main]+36

Thread[Thread-3,5,main]+35

Thread[Thread-1,5,main]+34

Thread[Thread-0,5,main]+33

Thread[Thread-2,5,main]+32

Thread[Thread-3,5,main]+31

Thread[Thread-1,5,main]+30

Thread[Thread-0,5,main]+29

Thread[Thread-2,5,main]+28

Thread[Thread-1,5,main]+27

Thread[Thread-3,5,main]+26

Thread[Thread-0,5,main]+25

Thread[Thread-2,5,main]+24

Thread[Thread-1,5,main]+23

Thread[Thread-3,5,main]+22

Thread[Thread-0,5,main]+21

Thread[Thread-2,5,main]+20

Thread[Thread-3,5,main]+19

Thread[Thread-1,5,main]+18

Thread[Thread-0,5,main]+17

Thread[Thread-2,5,main]+16

Thread[Thread-1,5,main]+15

Thread[Thread-3,5,main]+14

Thread[Thread-0,5,main]+13

Thread[Thread-2,5,main]+12

Thread[Thread-3,5,main]+11

Thread[Thread-1,5,main]+10

Thread[Thread-0,5,main]+9

Thread[Thread-2,5,main]+8

Thread[Thread-3,5,main]+7

Thread[Thread-0,5,main]+6

Thread[Thread-1,5,main]+6

Thread[Thread-2,5,main]+5

Thread[Thread-3,5,main]+4

Thread[Thread-1,5,main]+3

Thread[Thread-0,5,main]+2

Thread[Thread-3,5,main]+1

Thread[Thread-2,5,main]+0

Thread[Thread-0,5,main]+-1

Thread[Thread-1,5,main]+-2

最后还是出现了负数