信號量實現

public class PrintABCUsingSemaphore {
    private int times;
    private Semaphore semaphoreA = new Semaphore(1);
    private Semaphore semaphoreB = new Semaphore(0);
    private Semaphore semaphoreC = new Semaphore(0);

    public PrintABCUsingSemaphore(int times) {
        this.times = times;
    }

    
 
public static void main(String[] args) {
        PrintABCUsingSemaphore printABC = new PrintABCUsingSemaphore(10);

        // 非靜態方法引用  x::toString   和() -> x.toString() 是等價的！
        new Thread(printABC::printA).start();
        new Thread(printABC::printB).start();
        new Thread(printABC::printC).start();

        
 
/*new Thread(() -> printABC.printA()).start();
        new Thread(() -> printABC.printB()).start();
        new Thread(() -> printABC.printC()).start();
*/
    }

    public void printA() {
        try {
            print("A", semaphoreA, semaphoreB);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    
 
public void printB() {
        try {
            print("B", semaphoreB, semaphoreC);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public void printC() {
        try {
            print("C", semaphoreC, semaphoreA);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private void print(String name, Semaphore current, Semaphore next)
            throws InterruptedException {
        for (int i = 0; i < times; i++) {
            current.acquire();
            System.out.print(name);
            next.release();
        }
    }
}

多個線程順序打印問題