`CountDownLatch` + `Semaphore `思路清晰

CountDownLatch + Semaphore思路清晰

import java.util.Scanner;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Semaphore;
/**
*/
public class Main{  

    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            final int size = sc.nextInt();
            final char[] arr = new char[size * 4];

            final CountDownLatch cdl = new CountDownLatch(4);
            final Semaphore a = new Semaphore(1);
            final Semaphore b = new Semaphore(0);
            final Semaphore c = new Semaphore(0);
            final Semaphore d = new Semaphore(0);

            new Thread(() -> {
                for(int i = 0; i < arr.length; i+=4){
                    try{
                        a.acquire();
                    } catch (Exception e){}
                    arr[i] = 'A';
                    b.release();
                }
                cdl.countDown();
            }).start();

            new Thread(() -> {
                for(int i = 1; i < arr.length; i+=4){
                    try{
                        b.acquire();
                    } catch (Exception e){}
                    arr[i] = 'B';
                    c.release();
                }
                cdl.countDown();
            }).start();

            new Thread(() -> {
                for(int i = 2; i < arr.length; i+=4){
                    try{
                        c.acquire();
                    } catch (Exception e){}
                    arr[i] = 'C';
                    d.release();
                }
                cdl.countDown();
            }).start();

            new Thread(() -> {
                for(int i = 3; i < arr.length; i+=4){
                    try{
                        d.acquire();
                    } catch (Exception e){}
                    arr[i] = 'D';
                    a.release();
                }
                cdl.countDown();
            }).start();

            cdl.await();
            for(char c2 : arr){
                System.out.print(c2);
            }
            System.out.println();
        }
    }
}