Java Chapter 8.4: Static Variables and Methods

What is a static variable?

What is a static method?

Provide an example of a static method.

What is an example of defining a static method in a class?

Since static methods do not operate on an object, you cannot directly access any instance variables.

What is another name for static variables?

What are the uses of static variables?

Provide an example of a static variable using double as type and 'p' as the variable name.

Can static methods reference instance variables?

How can you define a static method?

Static methods allow services that are not really associated with an object.

How can a static method reference a variable?

Static Variables

Static variables are tied to the class itself rather than individual instances of the class.
Also known as class variables, there is only one instance of the variable shared across all objects of the class.

Static Methods

Static methods are invoked on the class, not on objects, allowing access to class-level functionality.
To define a static method, add the static modifier to the method declaration.

Access and Limitations

Static methods cannot directly access instance variables because these variables are tied to specific objects, which do not exist when the static method is executed.
Static methods can reference static variables and local variables declared within their own scope.

Usage of Static Variables

Static variables are useful for:
- Defining constants.
- Sharing data among all instances of a class.
- Acting as counters or accumulators applicable to the entire class.

Examples

Example of a static method defining a financial calculation:

public class Financial {
    public static double percentOf() { /* method body */ }
}

Example of declaring static variables:

static double p = 0;
static double QUARTER = .25;

Key Concepts

Since static methods do not work on objects, they support functionalities that are not inherently tied to object states.
Example misuse in static methods, like calling x.sqrt() is incorrect; proper usage is Math.sqrt(x), highlighting the need for object consistency.

Test your knowledge about static variables and methods in Java with this set of flashcards. Each card offers definitions and examples that clarify how static elements function within a class. Perfect for reinforcing key concepts in Java programming.