适配器模式

1.定义Task类，实现了Callable接口

public class Task implements Callable {
    private long num;
    public Task(Long num){
        this.num = num;
    }

    public Long call() throws Exception {
        long r = 0;
        for (long i = 0; i < this.num; i++) {
            r = r+i;
        }
        System.out.println(r);
        return r;
    }

2.开一个线程执行call方法

Callable callable = new Task(123L);
Thread thread = new Thread(callable);//编译错误，thread只能接受runnerable接口
thread.start();

3.用一个Adapter，把这个Callable接口“变成”Runnable接口

Callable callable = new Task(123L);
Thread thread = new Thread(new RunnableAdapter(callable));
thread.start();

4.定义RunnableAdapter适配器

public class RunnableAdapter implements Runnable{
    public Callable callable;

    public RunnableAdapter(Callable callable){
        this.callable = callable;
    }
    public void run() {
        try {
            callable.call();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

编写一个Adapter的步骤如下：

1. 实现目标接口，这里是Runnable；
2. 内部持有一个待转换接口的引用，这里是通过字段持有Callable接口；
3. 在目标接口的实现方法内部，调用待转换接口的方法。