这样的写法是不是都是为了让源代码更容易阅读？

commons-pool:public class StackKeyedObjectPool extends BaseKeyedObjectPool implements KeyedObjectPool

// BaseKeyedObjectPool 已经实现了KeyedObjectPool  这里还有必要再写 implements KeyedObjectPool吗？

public StackKeyedObjectPool() {
        this((KeyedPoolableObjectFactory)null,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);
    }
// (KeyedPoolableObjectFactory)null ？
public void clear() throws Exception, UnsupportedOperationException {
        throw new UnsupportedOperationException();
    }
// 因为父类的clear()方法中throws Exception，这里必须写throws Exception,但是有必要throws UnsupportedOperationException 吗？