Legal overridden method access

[Jacob Michaels]

My question is: What does mean to override a method. Can someone show me an example of this.
Thank you
The rules for overriding can be summarized as follows:
A private method may be overridden by a private, default, protected,
or public method.
A default method may be overridden by a default, protected, or public
method.
A protected method may be overridden by a protected or public
method.
A public method may only be overridden by a public method.

[Layne Lund]

Method overriding deals with inheritence, where the parent and child class each have a function with the same name. Run this example to see what happens:

public class Override
{
  public void main(String[] args)
  {
    Child c = new Child();
    Parent p = new Parent();
    c.func();
    p.func();
    p = c;
    p.func();
  }
}
class Parent
{
  public void func()
  {
    System.out.println("Parent class");
  }
}
class Child
  extends Parent
{
  public void func()
  {
    System.out.println("Child class");
  }
}

Actually, the last line in main() illustrates polymorphism, which is another topic closely related to method overriding. Before you run it, you should predict what you think the output will be. Then see if it is what you predicted.
Standard Disclaimer: the above code has not been compiled or tested. I created it from memory and should work as is. However, no warranty is given, explicit or implied. Use at your own risk.
HTH
Layne
[ March 26, 2003: Message edited by: Layne Lund ]

[Jacob Michaels]

Thank you
That helped!

[Barry Gaunt]

the parent and child class each have a function with the same name

This is also true of overloading, a totally different concept. So beware.
To override:

the methods must have the same name

the methods must have the same return type

the methods must have the same number of parameters

the methods' parameters must correspond one-to-one regarding the type of the parameters

the overriding method's access modifier must be of equal or weaker strictness (as original post)

The overriding method can only throw a subset (or none) of the exceptions declared in the throws clause of the overridden method.

(I've probably forgotten something else too)
A method having the same name but different parameter list (number of parameters, or type correspondence) is overloaded.
Examples are to be found in the Programmer Certification Forum.
[ March 27, 2003: Message edited by: Barry Gaunt ]
[ March 27, 2003: Message edited by: Barry Gaunt ]

[Layne Lund]

Originally posted by Barry Gaunt:

This is also true of overloading, a totally different concept. So beware.

Doh! Thank you for catching that. I meant to say "the parent and child class each have a function with the same signature," which is obviously very different. A methods signature is exactly what Barry described: the name and parameters.
Of course, it doesn't seem this is completely accurate, either. I didn't know that you have to have the exact same return type to override a method as well. I guess this makes sense because the compiler will be thoroughly confused if the parameter list and name are the same, but the return type is different. I should code up an example program to explore some of the issues involved here.

[Junilu Lacar]

Originally posted by Jacob Michaels:
A private method may be overridden by a private, default, protected,
or public method.

Check out Marlene Miller's comments in this thread regarding private methods