In Java, a variable is a named reference to a value that can be manipulated by the program. Variables are used to store information that is needed by the program, such as numbers, text, or object references.
Here are the basics of variables in Java:
1. Declaration: Before you can use a variable, you must declare it. To declare a variable, you specify the type of data it will hold, followed by the variable name. For example:
int age;
This declares a variable called `age` that can hold integer values.
2. Initialization: Once a variable is declared, you can assign a value to it using the assignment operator `=`. For example:
age = 25;
This assigns the value `25` to the `age` variable.
Alternatively, you can declare and initialize a variable in one step, like this:
int age = 25;
3. Types: In Java, variables have a type, which determines what kind of data they can hold. Common types include:
– `int`: integer values
– `double`: floating-point values
– `boolean`: true or false values
– `String`: text values
4. Naming conventions: Variable names must begin with a letter, underscore, or dollar sign, and can contain letters, numbers, underscores, and dollar signs. It’s generally a good practice to use descriptive names for variables.
5. Scope: Variables have a scope, which determines where they can be accessed in the program. A variable’s scope is determined by where it is declared. For example, a variable declared inside a method can only be accessed within that method.
6. Constants: In Java, you can declare a variable as a constant using the `final` keyword. A constant is a variable whose value cannot be changed once it is initialized. For example:
final double PI = 3.14159;
This declares a constant called `PI` that holds the value `3.14159`.