Java多线程与并发面试十大常考题目。

1 进程和线程的区别？

2 线程的start和run方法的区别.

package com.interview.javabasic.thread;

public class ThreadStartOrRunMethodDiff {

    public static void main(String[] args) {
        Thread t = new Thread() {
            public void run() {
                System.out.println(Thread.currentThread().getName());
            }
        };
        t.run();
    }

}

package com.interview.javabasic.thread;

public class ThreadStartOrRunMethodDiff {

    public static void main(String[] args) {
        Thread t = new Thread() {
            public void run() {
                System.out.println(Thread.currentThread().getName());
            }
        };
        t.start();
    }

}

3 Thread和Runnable的关系？

package com.interview.javabasic.thread;

public class MyRunnable implements Runnable {
    private String name;
    public MyRunnable(String name){
        this.name = name;
    }
    @Override
    public void run(){
        for(int i = 0 ; i < 10 ; i ++){
            System.out.println("Thread start : " + this.name + ",i= " + i);
        }
    }
}

package com.interview.javabasic.thread;

public class RunnableDemo {
    public static void main(String[] args) throws InterruptedException {
        MyRunnable mr1 = new MyRunnable("Runnable1");
        MyRunnable mr2 = new MyRunnable("Runnable2");
        MyRunnable mr3 = new MyRunnable("Runnable3");
        Thread t1 = new Thread(mr1);
        Thread t2 = new Thread(mr2);
        Thread t3 = new Thread(mr3);
        t1.start();
        t2.start();
        t3.start();
    }
}

4 如何实现处理线程的返回值？

成员变量传参，可以看上面的代码 MyRunnable的实现。

4 如何实现处理线程的返回值？

1 主线程等待法

package com.interview.javabasic.thread;

public class CycleWait implements Runnable{
    private String value;
    public void run() {
        try {
            Thread.currentThread().sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        value = "we have data now";
    }

    public static void main(String[] args) throws InterruptedException {
        CycleWait cw = new CycleWait();
        Thread t = new Thread(cw);
        t.start();
//        while (cw.value == null){
//            Thread.currentThread().sleep(100);
//        }
//        t.join();
        System.out.println("value : " + cw.value);
    }
}

结果如下：

主线程等待法，代码如下：

package com.interview.javabasic.thread;

public class CycleWait implements Runnable{
    private String value;
    public void run() {
        try {
            Thread.currentThread().sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        value = "we have data now";
    }

    public static void main(String[] args) throws InterruptedException {
        CycleWait cw = new CycleWait();
        Thread t = new Thread(cw);
        t.start();
        while (cw.value == null){
            Thread.currentThread().sleep(100);
        }
        System.out.println("value : " + cw.value);
    }
}

主线程等待法的缺点

1.无法做到精确的时间控制
2.成员变量多的话，一大堆if else

通过加入 join()方法

package com.interview.javabasic.thread;

public class CycleWait implements Runnable{
    private String value;
    public void run() {
        try {
            Thread.currentThread().sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        value = "we have data now";
    }

    public static void main(String[] args) throws InterruptedException {
        CycleWait cw = new CycleWait();
        Thread t = new Thread(cw);
        t.start();
       t.join();
        System.out.println("value : " + cw.value);
    }
}

package com.interview.javabasic.thread;

import java.util.concurrent.Callable;

public class MyCallable implements Callable<String> {
    @Override
    public String call() throws Exception{
        String value="test";
        System.out.println("Ready to work");
        Thread.currentThread().sleep(5000);
        System.out.println("task done");
        return  value;
    }

}

package com.interview.javabasic.thread;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

public class FutureTaskDemo {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        FutureTask<String> task = new FutureTask<String>(new MyCallable());
        new Thread(task).start();
        if(!task.isDone()){
            System.out.println("task has not finished, please wait!");
        }
        System.out.println("task return: " + task.get());

    }
}

线程池

package com.interview.javabasic.thread;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class ThreadPoolDemo {
    public static void main(String[] args) {
        ExecutorService newCachedThreadPool = Executors.newCachedThreadPool();
        Future<String> future = newCachedThreadPool.submit(new MyCallable());
        if(!future.isDone()){
            System.out.println("task has not finished, please wait!");
        }
        try {
            System.out.println(future.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        } finally {
            newCachedThreadPool.shutdown();
        }
    }
}

8-5 线程的状态？

package com.interview.javabasic.thread;

public class ThreadTest {
    private static void attack() {
        System.out.println("Fight");
        System.out.println("Current Thread is : " + Thread.currentThread().getName());
    }

    public static void main(String[] args) throws InterruptedException {
        Thread t = new Thread(){
            public void run(){
                attack();
            }
        };
        System.out.println("current main thread is : " + Thread.currentThread().getName());
        t.start();
        t.join();
        t.start();
    }
}