There are two types of methods.
- Instance methods are associated with an object and use the instance variables of that object. This is the default.
- Static methods use no instance variables of any object of the class they are defined in. If you define a method to be static, you will be given a rude message by the compiler if you try to access any instance variables. You can access static variables, but except for constants, this is unusual. Static methods typically take all they data from parameters and compute something from those parameters, with no reference to variables. This is typical of methods which do some kind of generic calculation. A good example of this are the many utility methods in the predefined Math class.
Calling static methods
There are two cases.
Called from within the same class
Just write the static method name. Eg,
Code:
// Called from inside the MyUtils class
double avgAtt = mean(attendance);
Called from outside the class
If a method (static or instance) is called from another class, something must be given before the method name to specify the class where the method is defined. For instance methods, this is the object that the method will access. For static methods, the class name should be specified. Eg,
Code:
// Called from outside the MyUtils class.
double avgAtt = MyUtils.mean(attendance);
If an object is specified before it, the object value will be ignored and the the class of the object will be used.
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