Java Ab中动态绑定和签名方法的问题

Question

Matching a method signature and binding a method implementation are two sepearate issue so ,what's wrong with the follows code?

Container c5 = new JButton();

Object c6 = new JButton();

c5.add(c6);       //----it is wrong,why?

for me , c5 is a reference variable which contain reference to object of JButton,and JButton extends the class Component,so it should be right so why ?

Answer 1

Java is a Single-Dispatch language. That means its method signature analysis is done at compile time, not run time.

The type of c6 is Object . (Yes, you assign a JButton , but the declared type of the variable is still Object .) So when Java looks at c5 (a Container ) and its methods, it doesn't see an add() method that takes an Object. So it flags it as an error.