Answer to Question #59581 in Java | JSP | JSF for Peter

Question

Give a definition of the following:

- Class method
- Instance method
- Class variable
- Instance variable

Answer 1

Class method
Class methods are methods which are declared as static. The method can be called without creating an instance of the class. Class methods can only operate on class members and not on instance members as class methods are unaware of instance members. Instance methods of the class can also not be called from within a class method unless they are being called on an instance of that class.

Instance method
Instance methods on the other hand require an instance of the class to exist before they can be called, so an instance of a class needs to be created by using the new keyword. Instance methods operate on specific instances of classes. Instance methods are not declared as static.

Class variable
Class variables, however, only have one copy of the variable(s) shared with all instances of the class. It’s important to remember that class variables are also known as static member variables in Java. Each object of the class does not have its own copy of a class variable. Instead, every object shares the one and only copy of that class variable – and any changes made to that copy are seen by all of the objects of that class.

Instance variable
Instance variables belong to an instance of a class. Another way of saying that is instance variables belong to an object, since an object is an instance of a class. Every object has it’s own copy of the instance variables.