Java实现两个线程交替打印1-100

思路1：synchronized 

public class ThreadTest {
    int i =1;
    boolean firstDone = false;
    Object lock = new Object();
    public static void main(String[] args) {
        ThreadTest t =new ThreadTest();
        t.print();
    }
    void print(){
        Thread t1 = new Thread(new Runnable() {
            public void run() {
                for(;i<=100;)
                {
                    synchronized (lock) {
                        if(!firstDone) {
                            System.out.println(Thread.currentThread().getName());
                            System.out.println(i++);
                            firstDone = true;
                            lock.notify();
                        }
                        else{
                            try {
                                lock.wait();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        });
        Thread t2 = new Thread(new Runnable() {
            public void run() {
                for(;i<=100;)
                {
                    synchronized (lock) {
                        if(firstDone) {
                            System.out.println(Thread.currentThread().getName());
                            System.out.println(i++);
                            firstDone = false;
                            lock.notify();
                        }
                        else {
                            try {
                                lock.wait();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        });
        t1.start();
        t2.start();
    }
}

思路2：信号量Semaphore

import java.util.concurrent.Semaphore;

public class ThreadTest2 {
    int i =1;
    Semaphore s1 = new Semaphore(1);
    Semaphore s2 = new Semaphore(0);
    public static void main(String[] args) {
        ThreadTest2 t = new ThreadTest2();
        t.print();
    }
    void print(){
        Thread t1 = new Thread(new Runnable() {
            public void run() {
                while(i<=100) {
                    try {
                        s1.acquire();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName());
                    System.out.println(i++);
                    s2.release();
                }
            }
        });

        Thread t2 = new Thread(new Runnable() {
            public void run() {
                while(i<=100) {
                    try {
                        s2.acquire();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName());
                    System.out.println(i++);
                    s1.release();
                }
            }
        });

        t1.start();
        t2.start();
    }
}

思路3：ReentrantLock + Condition

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class ThreadTest3 {
    int i =1;
    Lock lock = new ReentrantLock();
    Condition condition1 = lock.newCondition();
    Condition condition2 = lock.newCondition();
    boolean firstDone = false;
    public static void main(String[] args) {
        ThreadTest3 t = new ThreadTest3();
        t.print();
    }
    void print(){
        Thread t1 = new Thread(new Runnable() {
            public void run() {
                    while (i <= 100) {
                        lock.lock();
                        if(!firstDone) {
                            System.out.println(Thread.currentThread().getName());
                            System.out.println(i);
                            i++;
                            firstDone = true;
                            condition2.signal();
                        }
                        else {
                            try {
                                condition1.await();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                        lock.unlock();
                    }
            }
        });

        Thread t2 = new Thread(new Runnable() {
            public void run() {
                while (i <= 100) {
                    lock.lock();
                    if(firstDone) {
                        System.out.println(Thread.currentThread().getName());
                        System.out.println(i);
                        i++;
                        firstDone = false;
                        condition1.signal();
                    }
                    else {
                        try {
                            condition2.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    lock.unlock();
                }
            }
        });

        t1.start();
        t2.start();
    }
}