java编程思想练习题-第21章练习1-yield

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题目：实现一个Runnable。在run()内部打印一个消息，然后调用yield()。重复这个操作三次，然后从run中返回。在构造器中放置一条启动消息，并且放置一条在任务终止时的关闭消息。使用线程创建大量的这种任务并驱动他们。

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package test;
public class test {
public static void main(String[] args) {
// TODO Auto-generated method stub
for(int i=1;i<=10;i++){
new Thread(new runabletest()).start();;
}
}
}
class runabletest implements Runnable{
public String
startstr="start!";
public
String stopstr="stop!";
static int num=0;
public int id;
public runabletest(){
num++;
id=num;
startstr="#"+id+"
"+startstr;
stopstr="#"+id+"
"+stopstr;
System.out.println(startstr);
}
@Override
public void run() {
for(int i=1;i<=3;i++){
System.out.println("#"+id+" loop"+i);
Thread.yield();
}
System.out.println(stopstr);
}
}

结果是：

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#1
start!
#2
start!
#3
start!
#1 loop1
#2 loop1
#2 loop2
#1 loop2
#1 loop3
#1
stop!
#2 loop3
#2
stop!
#4
start!
#3 loop1
#3 loop2
#5
start!
#4 loop1
#3 loop3
#4 loop2
#3
stop!
#4 loop3
#4
stop!
#6
start!
#7
start!
#5 loop1
#5 loop2
#5 loop3
#5
stop!
#7 loop1
#6 loop1
#8
start!
#6 loop2
#7 loop2
#7 loop3
#6 loop3
#6
stop!
#7
stop!
#9
start!
#8 loop1
#8 loop2
#8 loop3
#8
stop!
#10
start!
#9 loop1
#9 loop2
#9 loop3
#9
stop!
#10 loop1
#10 loop2
#10 loop3
#10
stop!

如果把yield去掉的话结果是：

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#1
start!
#2
start!
#3
start!
#1 loop1
#1 loop2
#1 loop3
#1
stop!
#4
start!
#2 loop1
#5
start!
#2 loop2
#2 loop3
#2
stop!
#5 loop1
#5 loop2
#5 loop3
#5
stop!
#3 loop1
#3 loop2
#3 loop3
#3
stop!
#4 loop1
#4 loop2
#4 loop3
#4
stop!
#6
start!
#7
start!
#8
start!
#7 loop1
#7 loop2
#7 loop3
#7
stop!
#6 loop1
#6 loop2
#6 loop3
#6
stop!
#9
start!
#10
start!
#9 loop1
#9 loop2
#9 loop3
#9
stop!
#10 loop1
#10 loop2
#10 loop3
#10
stop!
#8 loop1
#8 loop2
#8 loop3
#8
stop!