今年,唯品会的一道笔试题是三个线程顺序打印ABC10次,当时写得很乱,也写错了,现在给出我的解决方法:
package deadLockThread;
public class PrintThread {
private static boolean flga1 = true;
private static boolean flga2 = false;
private static boolean flga3 = false;
public static void main(String[] args) {
final PrintThread o = new PrintThread();
Thread t1 = new Thread(new Runnable() {@Override
public void run() {
for (int i = 0;
i < 10;
i++) {
while (true) {
synchronized (o) {if (!flga1) {
try {
o.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}} else {
System.out.println(Thread.currentThread()
.getName());
flga1 = false;
flga2 = true;
flga3 = false;
o.notifyAll();
break;
}
}
}}}
}, "A");
Thread t2 = new Thread(new Runnable() {@Override
public void run() {for (int i = 0;
i < 10;
i++) {
while (true) {
synchronized (o) {
if (!flga2) {
try {
o.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}} else {
System.out.println(Thread.currentThread()
.getName());
flga1 = false;
flga2 = false;
flga3 = true;
o.notifyAll();
break;
}
}}
}}
}, "B");
Thread t3 = new Thread(new Runnable() {@Override
public void run() {for (int i = 0;
i < 10;
i++) {while (true) {
synchronized (o) {
if (!flga3) {
try {
o.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}} else {
System.out.println(Thread.currentThread()
.getName());
flga1 = true;
flga2 = false;
flga3 = false;
o.notifyAll();
break;
}
}}
}}
}, "C");
t1.start();
t2.start();
t3.start();
}}
【3个线程顺序打印ABC10次】其实,原理很简单,用三个标志来判断哪个线程应该wait 。在三个线程里面写入同步代码块,只有取得上面 o对象的对象锁,才能执行,这样保证同一时间只有一个线程在打印。配合wait 和notifyAll 还有三个标志就可以按照顺序打印ABC。
这是网上其他版本,我觉得他比我的好很多,代码简洁而且还是共用一个类,这样再增加线程也容易改动,很巧妙的使用AtomicInteger类 ,AtomicInteger类线程安全,适合在高并发中当计数器.
package com.mythread.test;
import java.util.concurrent.atomic.AtomicInteger;
public class T {
public static void main(String argv[]) {AtomicInteger synObj = new AtomicInteger(0);
TestPrint a = new TestPrint(synObj, "A", 0);
TestPrint b = new TestPrint(synObj, "B", 1);
TestPrint c = new TestPrint(synObj, "C", 2);
a.start();
b.start();
c.start();
}
}class TestPrint extends Thread {
private AtomicInteger synObj;
private String name;
private int flag;
private int count = 0;
public TestPrint(AtomicInteger synObj, String name, int flag) {
this.synObj = synObj;
this.name = name;
this.flag = flag;
}
@Override
public void run() {
while (true) {
synchronized (synObj) {
if (synObj.get() % 3 == flag) {
synObj.set(synObj.get() + 1);
System.out.println(name);
count++;
synObj.notifyAll();
if (count == 10) {
break;
}
} else {
try {
synObj.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
}
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