多线程经典笔试题集锦
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多线程经典笔试题集锦
题一
1、需求
要求用三个线程，线程1先打印1,2,3,4,5, 然后是线程2打印6,7,8,9,10, 然后是线程3打印11,12,13,14,15. 接着再由线程1打印16,17,18,19,20....以此类推，直到输出到45。
2、实现
package com.ctw.t1;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
* @author chentongwei@baidu-mgame.com 2018-11-22 16:51:26
* @Desc 要求用三个线程，线程1先打印1,2,3,4,5, 然后是线程2打印6,7,8,9,10, 然后是线程3打印11,12,13,14,15. 接着再由线程1打印16,17,18,19,20....以此类推，直到输出到45
*/
public class Demo {
public static void main(String[] args) {
Object lockObj = new Object();
ExecutorService threadPool = Executors.newFixedThreadPool(3);
threadPool.execute(new MyRunnable(0, lockObj));
threadPool.execute(new MyRunnable(1, lockObj));
threadPool.execute(new MyRunnable(2, lockObj));
threadPool.shutdown();
}
}
class MyRunnable implements Runnable {
private static int num = 1;
private int threadId;
private Object lockObj;
public MyRunnable(int threadId, Object lockObj) {
this.threadId = threadId;
this.lockObj = lockObj;
}
@Override
public void run() {
synchronized (lockObj) {
while (num <= 45) {
if (num / 5 % 3 == threadId) {
for (int i = 0; i < 5; i++) {
System.out.println("ThreadName: " + Thread.currentThread().getName() + ", num is: " + num ++);
}
lockObj.notifyAll();
} else {
try {
lockObj.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
}
3、结果
ThreadName: pool-1-thread-1, num is: 1
ThreadName: pool-1-thread-1, num is: 2
ThreadName: pool-1-thread-1, num is: 3
ThreadName: pool-1-thread-1, num is: 4
ThreadName: pool-1-thread-1, num is: 5
ThreadName: pool-1-thread-2, num is: 6
ThreadName: pool-1-thread-2, num is: 7
ThreadName: pool-1-thread-2, num is: 8
ThreadName: pool-1-thread-2, num is: 9
ThreadName: pool-1-thread-2, num is: 10
ThreadName: pool-1-thread-3, num is: 11
ThreadName: pool-1-thread-3, num is: 12
ThreadName: pool-1-thread-3, num is: 13
ThreadName: pool-1-thread-3, num is: 14
ThreadName: pool-1-thread-3, num is: 15
ThreadName: pool-1-thread-1, num is: 16
ThreadName: pool-1-thread-1, num is: 17
ThreadName: pool-1-thread-1, num is: 18
ThreadName: pool-1-thread-1, num is: 19
ThreadName: pool-1-thread-1, num is: 20
ThreadName: pool-1-thread-2, num is: 21
ThreadName: pool-1-thread-2, num is: 22
ThreadName: pool-1-thread-2, num is: 23
ThreadName: pool-1-thread-2, num is: 24
ThreadName: pool-1-thread-2, num is: 25
ThreadName: pool-1-thread-3, num is: 26
ThreadName: pool-1-thread-3, num is: 27
ThreadName: pool-1-thread-3, num is: 28
ThreadName: pool-1-thread-3, num is: 29
ThreadName: pool-1-thread-3, num is: 30
ThreadName: pool-1-thread-1, num is: 31
ThreadName: pool-1-thread-1, num is: 32
ThreadName: pool-1-thread-1, num is: 33
ThreadName: pool-1-thread-1, num is: 34
ThreadName: pool-1-thread-1, num is: 35
ThreadName: pool-1-thread-2, num is: 36
ThreadName: pool-1-thread-2, num is: 37
ThreadName: pool-1-thread-2, num is: 38
ThreadName: pool-1-thread-2, num is: 39
ThreadName: pool-1-thread-2, num is: 40
ThreadName: pool-1-thread-3, num is: 41
ThreadName: pool-1-thread-3, num is: 42
ThreadName: pool-1-thread-3, num is: 43
ThreadName: pool-1-thread-3, num is: 44
ThreadName: pool-1-thread-3, num is: 45
题二
1、需求
要求用三个线程，线程1先打印A,然后是线程2打印B, 然后是线程3打印C. 接着再由线程1打印A....以此类推，打印10次ABC
2、实现
package com.ctw.t1;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @author chentongwei@baidu-mgame.com 2018-11-22 17:34:58
* @Desc 要求用三个线程，线程1先打印A,然后是线程2打印B, 然后是线程3打印C. 接着再由线程1打印A....以此类推，打印10次ABC
*/
public class Demo1 {
public static void main(String[] args) {
Lock lock = new ReentrantLock();
ExecutorService threadPool = Executors.newFixedThreadPool(3);
threadPool.execute(new MyRunnable1("A", lock, 0));
threadPool.execute(new MyRunnable1("B", lock, 1));
threadPool.execute(new MyRunnable1("C", lock, 2));
threadPool.shutdown();
}
}
class MyRunnable1 implements Runnable {
private String str;
private Lock lock;
private int threadId;
private static int count = 0;
private static final int MAX = 30;
public MyRunnable1(String str, Lock lock, int threadId) {
this.str = str;
this.lock = lock;
this.threadId = threadId;
}
@Override
public void run() {
while (true) {
lock.lock();
// 为什么在这加判断，而不是在while里面写count<=MAX，因为那样的话会打印11次。
if (count >= MAX) {
lock.unlock();
return;
}
if (count % 3 == threadId) {
System.out.println(str);
count ++ ;
}
lock.unlock();
}
}
}
3、结果
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
题三
1、需求
现有三组字符串：ABC/DEF/GHI，要求用线程打印出A D G B E H C F I
2、实现
package com.ctw.t1;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @author chentongwei@baidu-mgame.com 2018-11-22 17:34:58
* @Desc： 现有三组字符串：ABC/DEF/GHI，要求用线程打印出A D G B E H C F I
*/
public class Demo2 {
public static void main(String[] args) {
Lock lock = new ReentrantLock();
ExecutorService threadPool = Executors.newFixedThreadPool(3);
threadPool.execute(new MyRunnable2("ABC", lock, 0));
threadPool.execute(new MyRunnable2("DEF", lock, 1));
threadPool.execute(new MyRunnable2("GHI", lock, 2));
threadPool.shutdown();
}
}
class MyRunnable2 implements Runnable {
private String str;
private Lock lock;
private int threadId;
private static int count = 0;
private static final int MAX = 9;
public MyRunnable2(String str, Lock lock, int threadId) {
this.str = str;
this.lock = lock;
this.threadId = threadId;
}
@Override
public void run() {
while (true) {
lock.lock();
// 为什么在这加判断，而不是在while里面写count<=MAX，因为那样的话会打印11次。
if (count >= MAX) {
lock.unlock();
return;
}
if (count % 3 == threadId) {
System.out.print(str.charAt(count / 3) + " ");
count ++ ;
}
lock.unlock();
}
}
}
3、结果
A D G B E H C F I
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