java多线程经典编程题

题目一：子线程循环2次，主线程循环2次，然后子线程循环2次，主线程循环2次，这样循环10次；

public class Demo2 {
    static class Mywork {
        private volatile boolean flag=true;//代表是否等待
        private synchronized void sub(){
            while (! flag){
                try {
                    this.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            for (int i = 0; i < 2; i++) {
                System.out.println("sub run "+ i);
            }
            flag=false;
            this.notify();
        }
        private synchronized void mainRun(){
            while (flag){
                try {
                    this.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            for (int i = 0; i < 2; i++) {
                System.out.println("main run----------- "+i);
            }
            flag=true;
            this.notify();
        }
    }
    public static void main(String[] args) {
        Mywork mywork=new Mywork();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    mywork.sub();
                }
            }
        }).start();

        for (int i = 0; i < 10; i++) {
            mywork.mainRun();
        }
    }
}

打印结果：

sub run 0
sub run 1
main run----------- 0
main run----------- 1
sub run 0
sub run 1
main run----------- 0
main run----------- 1
...
...此处省略
...
sub run 0
sub run 1
main run----------- 0
main run----------- 1

用显示锁的方式：

public class LockCondtionDemo {
    private static class Mywork{
        private volatile boolean flag=true;//是否等待
        private Lock lock=new ReentrantLock();
        private Condition condition=lock.newCondition();
        public void sub(){
            try{
                lock.lock();
                while (!flag){
                    try {
                        condition.await();//释放锁
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println("sub run ----------------");
                flag=false;
                condition.signal();
            }finally {
                lock.unlock();//这里一定要释放锁
            }
        }
        public void main(){
            try{
                lock.lock();
                while(flag){
                    try {
                        condition.await();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println("main run");
                flag=true;
                condition.signal();
            }finally {
                lock.unlock();
            }
        }
    }
    public static void main(String[] args) {
        Mywork mywork=new Mywork();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 5; i++) {
                    mywork.sub();
                }
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 5; i++) {
                    mywork.main();
                }
            }
        }).start();
    }
}

题目二：写两个线程，一个线程打印1_{52，另一个线程打印A}Z，打印顺序是12A34B...5152Z；

public class Demo1 {
    static class Behaver{
        private volatile boolean flag=true;
        private int count=1;
        public synchronized void printNum(){
            while(!flag){
                try {
                    this.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.print(count*2-1);
            System.out.print(count*2);
            flag=false;
            this.notify();
        }
        public synchronized void printChar(){
            while(flag){
                try {
                    this.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.print((char)(count+'A'-1));
            count++;
            flag = true;
            this.notify();
        }
    }

    public static void main(String[] args) {
        Behaver behaver=new Behaver();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 26; i++) {
                    behaver.printNum();
                }
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 26; i++) {
                    behaver.printChar();
                }
            }
        }).start();
    }
}

打印结果：

12A34B56C78D910E1112F1314G1516H1718I1920J2122K2324L2526M2728N2930O3132P3334Q3536R3738S3940T4142U4344V4546W4748X4950Y5152Z