java - 在构造函数后面有一个覆盖方法的部分的 Java 语法是什么？

Question

这个问题已经有答案了:

How are Anonymous inner classes used in Java? (18 个回答)

已关闭 6 年前。

我找到了这个example使用以下代码:

CompletableFuture<T> completable = new CompletableFuture<T>() {  
    @Override  
    public boolean cancel(boolean mayInterruptIfRunning) {  
        // propagate cancel to the listenable future  
        boolean result = listenableFuture.cancel(mayInterruptIfRunning);  
        super.cancel(mayInterruptIfRunning);  
        return result;  
    }  
};  

这个语法是什么意思？该方法是否重写了类中的方法而不扩展它？

Answer 1

这段代码创建了一个 anonymous subclass CompletableFuture。这个匿名子类覆盖 cancel(bool)方法与新的实现。匿名子类相当于创建一个扩展 CompleteableFuture 的新类，但需要注意的是，在其他地方重用这个新子类并不简单。

@Override 在这种情况下并不是绝对必要的，但它为您提供了一些好处，如 this question 的答案所述。 :

Use it every time you override a method for two benefits. Do it so that you can take advantage of the compiler checking to make sure you actually are overriding a method when you think you are. This way, if you make a common mistake of misspelling a method name or not correctly matching the parameters, you will be warned that you method does not actually override as you think it does. Secondly, it makes your code easier to understand because it is more obvious when methods are overwritten.

Additionally, in Java 1.6 you can use it to mark when a method implements an interface for the same benefits. I think it would be better to have a separate annotation (like @Implements), but it's better than nothing.