I.3: OVERRIDING METHODS

OBJECTIVE

I can:

override a method in a superclass/subclass relationship

A subclass inherits all public methods from its superclass, and these methods remain public in the subclass.

But, we usually add more methods or instance variables to the subclass.

Sometimes, we want to modify existing inherited methods.

This is called overriding methods.

Overriding an inherited method means providing a public method in a subclass with the same method signature (method name, parameter type list and return type) as the public method in the superclass.

The method in the subclass will be called instead of the method in the superclass.

One common method that is overridden is the toString() method.

The example below shows a similar method called greet().

The MeanGreeter inherits the greet() method from Greeter, but then overrides it:

Note: To override an inherited method, the method in the child class must have the same name, parameter list, and return type (or a subclass of the return type) as the parent method.

Any method that is called must be defined within its own class or its superclass.

You may see the @Override annotation above a method.

This is optional but it provides an extra compiler check that you have matched the method signature exactly.

OVERLOADING METHODS

Don't get overriding a method confused with overloading a method!

Overloading a method is when several methods have the same name but the parameter types, order, or number are different.

So with overriding, the method signatures look identical but they are in different classes, but in overloading, only the method names are identical and they have different parameters.

The example below the greet(String who) method overloads the greet() method of Greeter.

Notice that MeanGreeter inherits this method and it isn't overridden:

Note: To overload a method the method must have the same name, but the parameter list must be different in some way. It can have a different number of parameters, different types of parameters, and/or a different order for the parameter types. The return type can also be different.

INHERITED GET/SET METHODS

Inheritance means that an object of the child class automatically includes the object instance variables and methods defined in the parent class.

But, if the inherited instance variables are private, which they should be, the child class can not directly access them using dot notation.

The child class can use public accessors (also called getters or get methods) which are methods that get instance variable values and public mutators (also called modifier, setters, or set methods) which set their values.

For example, if a parent has a private instance variable, name, then the parent typically provides a public getName method and a public setName method as shown below.

In the setName method, the code checks if the passed string is null before it sets it and returns true if the set was successful or false otherwise.

The Employee class inherits the name field but must use the public method getName and setName to access it.

SUMMARY

Method overriding occurs when a public method in a subclass has the same method signature as a public method in the superclass.
Any method that is called must be defined within its own class or its superclass.
A subclass is usually designed to have modified (overridden) or additional methods or instance variables.
A subclass will inherit all public methods from the superclass (for example all the set and get methods); these methods remain public in the subclass.
Overloading a method is when several methods have the same name but the parameter types, order, or number are different.

EVIDENCE

1) Complete the following Google Form. This form must be 100% correct and includes released AP practice questions. To stop working and return later, hit submit! You can "edit your response" and continue where you left off.

I.3 Evidence

2) Create Your Own Assignment! Remember, the OBJECTIVE of this lesson is to be able to override a method in a superclass/subclass relationship. What EVIDENCE can you present to prove that you can do this? Meet with Mr. C when you are ready to present. In other words, show me what you can do!

3) MC Exam Practice: This lesson has additional practice problems which can be found on the MC Exam Practice page with an answer key! Use ctrl + f to search for different objectives throughout the year. You could look at these questions now, or, save these practice questions for later and use them to review! The choice is yours.

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I.3: OVERRIDING METHODS

OBJECTIVE

A subclass inherits all public methods from its superclass, and these methods remain public in the subclass.

But, we usually add more methods or instance variables to the subclass.

Sometimes, we want to modify existing inherited methods.

This is called overriding methods.

Overriding an inherited method means providing a public method in a subclass with the same method signature (method name, parameter type list and return type) as the public method in the superclass.

The method in the subclass will be called instead of the method in the superclass.

One common method that is overridden is the toString() method.

The example below shows a similar method called greet().

The MeanGreeter inherits the greet() method from Greeter, but then overrides it:

Note: To override an inherited method, the method in the child class must have the same name, parameter list, and return type (or a subclass of the return type) as the parent method.

Any method that is called must be defined within its own class or its superclass.

You may see the @Override annotation above a method.

This is optional but it provides an extra compiler check that you have matched the method signature exactly.

OVERLOADING METHODS

Don't get overriding a method confused with overloading a method!

Overloading a method is when several methods have the same name but the parameter types, order, or number are different.

So with overriding, the method signatures look identical but they are in different classes, but in overloading, only the method names are identical and they have different parameters.

The example below the greet(String who) method overloads the greet() method of Greeter.

Notice that MeanGreeter inherits this method and it isn't overridden:

Note: To overload a method the method must have the same name, but the parameter list must be different in some way. It can have a different number of parameters, different types of parameters, and/or a different order for the parameter types. The return type can also be different.

INHERITED GET/SET METHODS

Inheritance means that an object of the child class automatically includes the object instance variables and methods defined in the parent class.

But, if the inherited instance variables are private, which they should be, the child class can not directly access them using dot notation.

The child class can use public accessors (also called getters or get methods) which are methods that get instance variable values and public mutators (also called modifier, setters, or set methods) which set their values.

For example, if a parent has a private instance variable, name, then the parent typically provides a public getName method and a public setName method as shown below.

In the setName method, the code checks if the passed string is null before it sets it and returns true if the set was successful or false otherwise.

The Employee class inherits the name field but must use the public method getName and setName to access it.

SUMMARY

Method overriding occurs when a public method in a subclass has the same method signature as a public method in the superclass.

Any method that is called must be defined within its own class or its superclass.

A subclass is usually designed to have modified (overridden) or additional methods or instance variables.

A subclass will inherit all public methods from the superclass (for example all the set and get methods); these methods remain public in the subclass.

Overloading a method is when several methods have the same name but the parameter types, order, or number are different.

EVIDENCE

1) Complete the following Google Form. This form must be 100% correct and includes released AP practice questions. To stop working and return later, hit submit! You can "edit your response" and continue where you left off.

I.3 Evidence

2) Create Your Own Assignment! Remember, the OBJECTIVE of this lesson is to be able to override a method in a superclass/subclass relationship. What EVIDENCE can you present to prove that you can do this? Meet with Mr. C when you are ready to present. In other words, show me what you can do!