Java交替打印两个字符串

一、使用volatile关键字

public class Main {
volatile int x = 0;

Main() {
    new Thread(() -> {
        while (x < 100) {
            while (x % 2 == 0) ;
            System.out.print("A");
            x++;
        }
    }).start();
    new Thread(() -> {
        while (x < 100) {
            while (x % 2 == 1) ;
            System.out.print("B");
            x++;
        }
    }).start();
}

public static void main(String[] args) {
    new Main();
}
}

二、使用atomicInteger

import java.util.concurrent.atomic.AtomicInteger;

public class Main {

Main() {
    final AtomicInteger x = new AtomicInteger(0);
    new Thread(() -> {
        while (x.get() < 100) {
            while (x.get() % 2 == 0) ;
            System.out.print("A");
            x.incrementAndGet();
        }
    }).start();
    new Thread(() -> {
        while (x.get() < 100) {
            while (x.get() % 2 == 1) ;
            System.out.print("B");
            x.incrementAndGet();
        }
    }).start();
}

public static void main(String[] args) {
    new Main();
}
}

三、使用锁

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

public class Main {
Lock x = new ReentrantLock();
int index = 0;

Main() {
    new Thread(() -> {
        boolean over = false;
        while (!over) {
            if (index % 2 == 0) {
                x.lock();
                if (index % 2 == 0) {
                    System.out.print("A");
                    index++;
                }
                over = index > 100;
                x.unlock();
            }
        }
    }).start();
    new Thread(() -> {
        boolean over = false;
        while (!over) {
            if (index % 2 == 1) {
                x.lock();
                if (index % 2 == 1) {
                    System.out.print("B");
                    index++;
                }
                over = index > 100;
                x.unlock();
            }
        }
    }).start();
}

public static void main(String[] args) {
    new Main();
}
}

四、使用synchronized关键字

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

public class Main {
int index = 0;

Main() {
    new Thread(() -> {
        boolean over = false;
        while (!over) {
            if (index % 2 == 0) {
                synchronized (this) {
                    if (index % 2 == 0) {
                        System.out.print("A");
                        index++;
                    }
                    over = index > 100;
                }
            }
        }
    }).start();
    new Thread(() -> {
        boolean over = false;
        while (!over) {
            if (index % 2 == 1) {
                synchronized (this) {
                    if (index % 2 == 1) {
                        System.out.print("B");
                        index++;
                    }
                    over = index > 100;
                }
            }
        }
    }).start();
}

public static void main(String[] args) {
    new Main();
}
}

五、使用Python

JavaScript是单线程的，Python可以实现多线程，但是Python的多线程不能充分利用多核。

这就相当于Python天生就不需要volatile。

a = "床前明月光疑是地上霜"
from threading import Thread

index = 0

def one():
    global index
    while index < len(a):
        while index % 2 == 0:
            pass
        if index >= len(a): break
        print(a[index])
        index += 1

def two():
    global index
    while index < len(a):
        while index % 2 == 1:
            pass
        if index >= len(a): break
        print(a[index])
        index += 1

Thread(target=one).start()
Thread(target=two).start()