JAVA多线程

进程：程序的执行过程（动态概念）。它持有资源（内存、文件）和线程。

线程：程序执行流的最小单元。线程共享进程的资源。

线程的交互：互斥（竞争）和同步（合作）。

题目：有A,B,C三个线程，A线程输出A，B线程输出B，C线程输出C，要求，同时启动三个线程，按顺序输出ABC，循环10次。

PrintLetter.java:

public class PrintLetter
{
    private char letter = 'A';
    
    public char getLetter()
    {
        return letter;
    }

    public void next()
    {
        letter = (char) ((letter - 64) % 3 + 65);
    }
    
    public void print()
    {
        System.out.print(letter);
    }
}

ThreeThreadPrintABC.java:

public class ThreeThreadPrintABC
{
    public static void main(String[] args)
    {
        ThreeThreadPrintABC foo = new ThreeThreadPrintABC();
        PrintLetter printLetter = new PrintLetter();
        Thread a = new Thread(foo.new PrintRunnable(printLetter, 'A'));
        Thread b = new Thread(foo.new PrintRunnable(printLetter, 'B'));
        Thread c = new Thread(foo.new PrintRunnable(printLetter, 'C'));
        a.start();
        b.start();
        c.start();
    }
    
    private class PrintRunnable implements Runnable
    {
        private char letter;
        private PrintLetter printLetter;
        
        public PrintRunnable(PrintLetter printLetter, char letter)
        {
            this.printLetter = printLetter;
            this.letter = letter;
        }
        
        public void run()
        {
            for(int i = 0; i < 10; i++)
            {
                synchronized(printLetter)
                {
                    while(letter != printLetter.getLetter())
                    {
                        try 
                        {
                            printLetter.wait();
                        } 
                        catch (InterruptedException e) 
                        {
                            e.printStackTrace();
                        }
                    }
                    printLetter.print();
                    printLetter.next();
                    printLetter.notifyAll();
                }
            }
        }
    }
}

OR:

public class ThreeThreadPrintABC
{
    private int state = 0;
    private Object obj = new Object();
    
    public static void main(String[] args)
    {
        ThreeThreadPrintABC foo = new ThreeThreadPrintABC();
        Thread a = new Thread(foo.new PrintRunnable('A'));
        Thread b = new Thread(foo.new PrintRunnable('B'));
        Thread c = new Thread(foo.new PrintRunnable('C'));
        a.start();
        b.start();
        c.start();
    }
    
    private class PrintRunnable implements Runnable
    {
        private char letter;

        
        public PrintRunnable(char letter)
        {
            this.letter = letter;
        }
        
        public void run()
        {
            while(state < 30)
            {
                synchronized(obj)
                {
                    if(letter == state % 3 + 65)
                    {
                        System.out.print(letter);
                        letter = (char) ((letter - 64) % 3 + 65);
                        state++;
                    }
                }
            }
        }
    }
}