Java - Calling functions in extended classes through an object array

问题

I've got an array of objects, some of which use an extended version which contains a function not available in the base class. How can I call that function through the array when the array is defined by the base class?

Example

Shape[] shapes = new Shape[10];

shapes[0] = new Circle(10) //10 == radius, only exists in circle class which extends Shape

shapes[0].getRadius(); //Gives me a compilation error as getRadius() doesn't exist in the      
Shape class, only in the extended Circle class. Is there a way around this?

回答1:

Shape class does not contain the method getRadius and hence without casting the object of Shape to Circle, the method will not be visible. So you should use this:

((Circle)shapes[0]).getRadius();

回答2:

If you're sure your object is of a given subclass, use cast:

((Circle)shapes[0]).getRadius();

回答3:

try this

if (shapes[0] instanceof Circle) 
       ((Circle)shapes[0]).getRadius();

来源：https://stackoverflow.com/questions/18285130/java-calling-functions-in-extended-classes-through-an-object-array