Future模式, 等会儿再来拿

假设有一个方法需要花费很长时间才能获取运行结果。
那么，与其一直等待结果，不如先拿一张“提货单”。
获取提货单并不耗费时间。
过一段时间后再来拿结果.

    public static void main(String[] args) {
        Host host = new Host();

        // 预定蛋糕
        FutureData futureData = host.provideCake("didi");
        FutureData futureData1 = host.provideCake("dog");
        FutureData futureData2 = host.provideCake("cat");
        FutureData futureData3 = host.provideCake("bear");

        // 取蛋糕
        System.out.println(futureData.getData());
        System.out.println(futureData1.getData());
        System.out.println(futureData2.getData());
        System.out.println(futureData3.getData());

    }

public class Host {

    public FutureData provideCake(String cakeName) {
        // 开提货单
        FutureData futureData = new FutureData();

        // 通知师傅做蛋糕
        new Thread(() -> {
            RealData realData = new Worker().makeCake(cakeName);
            // 将蛋糕发给顾客
            futureData.setData(realData);
        }).start();

        // 返回提货单
        return futureData;
    }

}

public class Worker {

    public RealData makeCake(String cakeName) {
        RealData realData = new RealData();
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        realData.setContent(cakeName);
        return realData;
    }
}

public class FutureData {

    // 蛋糕
    private String content;

    public synchronized void setData(RealData realData) {
        this.content = realData.getContent();
        notifyAll();
    }

    public synchronized String getData() {
        // 如果蛋糕还没有做好, 就等待
        if (content == null) {
            try {
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        return this.content;
    }

}

public class RealData {

    private String content;

    public void setContent(String content) {
        this.content = content;
    }

    public String getContent() {
        return this.content;
    }

}