Java Variables | Java Tutorial

Variables are containers that store information that can be manipulated and referenced later by the programmer within the code. Java variables have a data type associated with them which can tell us about the size and layout of the variable’s memory.

Syntax:

datatype variable = value

There are three types of variables in Java:

Local variable
Instance variable
Class/Static variable

A. Local Variables:

A variable that is declared inside the body of the method or constructor is called a local variable. It is called so because the extent of a local variable lies only within the method or constructor within which it is created and other methods in the class cannot access it.

Inside the method body, a local variable is declared using the static keyword.

Example:

public class variableType {
    public void localVariable() {
        String name = "Ben";
        int marks = 95;
        System.out.println(name + " Scored " + marks + "%.");
    }
 
    public static void main(String[] args) {
        variableType vt = new variableType();
        vt.localVariable();
    }
}

Output:

Ben Scored 95%.

If it is accessed outside the method or constructor within which it is created, then it gives an error.

Example:

public class variableType {
    public void localVariable() {
        String name = "Ben";
        int marks = 95;
    }
    public void notLocalVariable() {
        System.out.println(name + " Scored " + marks + "%.");
    }
 
    public static void main(String[] args) {
        variableType vt = new variableType();
        vt.notLocalVariable();
    }
}

Output:

name cannot be resolved to a variable
marks cannot be resolved to a variable

B. Instance Variables:

An instance variable is declared inside the class but outside a method or a constructor. It is similar to a static variable except that it is declared without using the keyword static. These variables are accessible by all methods or constructors that are inside the class.

Example:

public class variableType {
 
    public String name = "Ben";
    public int marks = 95;
 
    public void instanceVariable() {
        System.out.println(name + " Scored " + marks + "%.");
    }
 
    public static void main(String[] args) {
        variableType vt = new variableType();
        vt.instanceVariable();
    }
}

Output:

Ben Scored 95%.

C. Class/Static Variables:

A static variable is declared inside the class but outside a method or a constructor. It is similar to an instance variable except that it is declared using the keyword static. These variables are accessible by all methods or constructors that are inside the class.

Example:

public class variableType {
 
    public static String name;
    public static int marks;
 
    public static void main(String[] args) {
        name = "Ben";
        marks = 95;
        System.out.println(name + " Scored " + marks + "%.");
    }
}

Output:

Ben Scored 95%.

If a variable is not declared static then it gives an error.

Example:

public class variableType {
    public String name;
    public int marks;
 
    public static void main(String[] args) {
        name = "Ben";
        marks = 95;
        System.out.println(name + " Scored " + marks + "%.");
    }
}

Output:

Cannot make a static reference to a non-static field