关于多线程中使用while做循环而不使用if的解释

Java代码









package com.thread.example;

import java.util.LinkedList;

public class Example10 {

private LinkedList<Object> myList = new LinkedList<Object>();

private int MAX = 10;

public Example10() {

super();

}

public void start(){

new Producerder().start();

new Consumereder().start();

}

class Producerder extends Thread {

@Override

public void run() {

for (int i = 0; i < 15; i++) {

try {

this.sleep(1000);

} catch (Exception e) {

e.printStackTrace();

}

synchronized (myList) {

try {

while(myList.size() == MAX){

System.out.println("warning: it's full!");

myList.wait();

}

//*************把这一段注释掉********************

Object o = new Object();

if(myList.add(o)){

System.out.println("Producer: " + o);

myList.notify();

}

//*******************************

//把上面注释掉后,启用下面一行后。你再在Consumereder中分别是用while和if看下输出结果

//myList.notify();

} catch (Exception e) {

System.out.println("producer is interrupted!");

}

}

}

}

}

class Consumereder extends Thread {

@Override

public void run() {

for (int i = 0; i < 15; i++) {

try {

this.sleep(100);

} catch (Exception e) {

e.printStackTrace();

}

synchronized (myList) {

try {

while(myList.size() == 0){

System.out.println("warning: it's empty!");

myList.wait();

}

System.out.println("oooooooooooooooooo");

Object o = myList.removeLast();

System.out.println("Consumereder" + o);

myList.notify();

} catch (Exception e) {

System.out.println("consumer is interrupted!");

}

}

}

}

}

public static void main(String[] args) {

Example10 ex10 = new Example10();

ex10.start();

}

}

package com.thread.example;

import java.util.LinkedList;

public class Example10 {

private LinkedList<Object> myList = new LinkedList<Object>();

private int MAX = 10;

public Example10() {
super();
}

public void start(){
new Producerder().start();
new Consumereder().start();
}

class Producerder extends Thread {

@Override
public void run() {
for (int i = 0; i < 15; i++) {
try {
this.sleep(1000);
} catch (Exception e) {
e.printStackTrace();
}
synchronized (myList) {
try {
while(myList.size() == MAX){
System.out.println("warning: it's full!");
myList.wait();
}

//*************把这一段注释掉********************
Object o = new Object();
if(myList.add(o)){
System.out.println("Producer: " + o);
myList.notify();
}
//*******************************
//把上面注释掉后,启用下面一行后。你再在Consumereder中分别是用while和if看下输出结果
//myList.notify();
} catch (Exception e) {
System.out.println("producer is interrupted!");
}
}
}
}

}

class Consumereder extends Thread {

@Override
public void run() {
for (int i = 0; i < 15; i++) {
try {
this.sleep(100);
} catch (Exception e) {
e.printStackTrace();
}

synchronized (myList) {
try {
while(myList.size() == 0){
System.out.println("warning: it's empty!");
myList.wait();
}
System.out.println("oooooooooooooooooo");
Object o = myList.removeLast();
System.out.println("Consumereder" + o);
myList.notify();
} catch (Exception e) {
System.out.println("consumer is interrupted!");
}
}
}
}

}

public static void main(String[] args) {
Example10 ex10 = new Example10();
ex10.start();
}
}

注：根据代码中注释的操作运行一次，你就明白什么意思了;

如果生产者没有生产，就调用唤醒(notify)。消费者的判断会出问题(如果使用if)

这就是为什么使用while而不是if的原因