Java Variable Types Flashcards

Study Notes

Variables in Java

A variable is a named storage that programs can manipulate.
Each variable has a specified type affecting its memory layout, value range, and applicable operations.

Data Types

Java supports various data types crucial for defining the nature of variables.

Variable Naming

The name given to each variable is referred to as the variable.

Types of Variables

Java has three kinds of variables:
- Local variables
- Instance variables
- Class/static variables

Local Variables

Declared within methods, constructors, or blocks, local variables exist only during execution of that method, constructor, or block.
They cannot utilize access modifiers and have no default values, thus requiring initialization before use.
Visibility is limited to the method, constructor, or block they are declared in.
Local variables occupy stack memory.

Instance Variables

Declared within a class but outside any methods, constructors, or blocks.
Created when an object is instantiated using the new keyword, and are destroyed when the object is no longer in use.
Hold values referenced by multiple methods or represent the state of an object.
May be declared before or after use and can have access modifiers.
Typically designated as private but can be made visible to subclasses.
Instance variables have default values (0 for numbers, false for Booleans, and null for object references) and can be initialized during declaration or in constructors.

Class/Static Variables

Declared with the static keyword in a class, outside methods, constructors, or blocks, resulting in a single copy regardless of object instantiation.
Often declared as constants, which are public/private, final, and static — they maintain their initial value.
Created upon program start and destroyed when the program terminates.
Visibility follows similar rules to instance variables, with many being public for user access.
Default values mirror those of instance variables; can also be initialized in static initializer blocks.
Accessed through ClassName.VariableName if public; constant variable names are in uppercase when declared as public static final.

Description

Test your knowledge of variable types in Java with these flashcards. Each card presents a key concept, helping you understand variables and data types in programming. Perfect for students learning Java fundamentals.