记录面试过程中被问到的几个需要手写代码的小案例

1.请手写出线程的等待唤醒机制

案例中两个线程：SyncSetThread设置学生信息，SyncGetThread用来获取学生信息，在Student实体中提供一个标记属性flag，记录当前是否有数据。

等待唤醒机制

设置信息线程SyncSetThread

/*

* 使用Object的wait() 和 notify() 来实现等待唤醒机制

* Created by JackYang on 2017/10/17.

*/

class SyncSetThread implements Runnable {

private final Student student;

SyncSetThread(Student student) {

this.student = student;

}

@Override

public void run() {

int num = 0;

while (true) {

synchronized (student) {

if (student.flag) {

try {

student.wait();

} catch (InterruptedException e) {

e.printStackTrace();

}

}

if (num % 2 == 0) {

student.name = "JackYang";

student.age = 26;

} else {

student.name = "江一燕";

student.age = 28;

}

++num;

student.flag = true;

student.notify();

//此时唤醒，SyncSetThread和SyncGetThread两个线程都有同等的机会去抢占资源

}

}

}

}

获取信息线程SyncGetThread

class SyncGetThread implements Runnable {

private final Student student;

SyncGetThread(Student student) {

this.student = student;

}

@Override

public void run() {

while (true) {

synchronized (student) {

if (!student.flag) {

try {

//对象中没有数据的时候就等待

student.wait();

} catch (InterruptedException e) {

e.printStackTrace();

}

}

System.out.println(student.name + "---" + student.age);

//数据消费完了(取出后)改变标记

student.flag = false;

student.notify();

//此时唤醒，SyncSetThread和SyncGetThread两个线程都有同等的机会去抢占资源

}

}

}

}

测试入口

/*

* 线程的等待唤醒机制，实现一人一次有规律

* Created by JackYang on 2017/10/17.

*/

public class TestSyncThread {

public static void main(String[] args) {

Student student = new Student();

SyncSetThread syncSetThread = new SyncSetThread(student);

SyncGetThread syncGetThread = new SyncGetThread(student);

Thread thread1 = new Thread(syncSetThread);

Thread thread2 = new Thread(syncGetThread);

thread1.start();

thread2.start();

}

}

2.请手写出线程死锁代码

这个没得商量，直接上代码

/**

* 死锁代码

* Created by JackYang on 2017/10/17.

*/

class DieThread extends Thread {

private boolean flag;

DieThread(boolean flag) {

this.flag = flag;

}

@Override

public void run() {

if (flag) {

//防止一次卡不住

while (true) {

synchronized (MyLock.lockA) {

System.out.println("true lockA");

synchronized (MyLock.lockB) {

System.out.println("true lockB");

}

}

}

} else {

while (true) {

synchronized (MyLock.lockB) {

System.out.println("false lockB");

synchronized (MyLock.lockA) {

System.out.println("false lockA");

}

}

}

}

}

}