学步园

来至《java多线程设计模式》

对于一个执行起来需要花些时间的方法，不等待执行结果出来，而是获取一张替代的“提货单”。

使用异步方法调用，分离准备返回值和使用返回值。

public class Main {
    public static void main(String[] args) {
        System.out.println("main BEGIN");
        Host host = new Host();
        Data data1 = host.request(10, 'A');
        Data data2 = host.request(20, 'B');
        Data data3 = host.request(30, 'C');

        System.out.println("main otherJob BEGIN");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
        }
        System.out.println("main otherJob END");

        System.out.println("data1 = " + data1.getContent());
        System.out.println("data2 = " + data2.getContent());
        System.out.println("data3 = " + data3.getContent());
        System.out.println("main END");
    }
}

 

public class FutureData implements Data {
    private RealData realdata = null;
    private boolean ready = false;
    public synchronized void setRealData(RealData realdata) {
        if (ready) {                        
            return;     // balk
        }
        this.realdata = realdata;
        this.ready = true;
        notifyAll();
    }
    public synchronized String getContent() {
        while (!ready) {
            try {
                wait();
            } catch (InterruptedException e) {
            }
        }
        return realdata.getContent();
    }
}

Host类

public class Host {
    public Data request(final int count, final char c) {
        System.out.println("    request(" + count + ", " + c + ") BEGIN");

        // (1) 建立FutureData的实体
        final FutureData future = new FutureData();

        // (2) 为了建立RealData的实体，启动新的线程
        new Thread() {                                      
            public void run() {                             
                RealData realdata = new RealData(count, c);
                future.setRealData(realdata);
            }                                               
        }.start();                                          

        System.out.println("    request(" + count + ", " + c + ") END");

        // (3) 取回FutureData实体，作为传回值
        return future;
    }
}