Java - Declaration, Initialization, and Assignment

Declaration

Before a variable can be used in a Java program, it must be declared.

The following code shows how to declare a variable.

int num1; // Declaration of a variable num1 

Assignment

The following code declares an int variable num2 and assigns 50 to it:

int num2;   // Declaration of a variable num2 
num2 = 50;  // Assignment 

Demo

public class Main {
  public static void main(String[] args) {
    int num2;   // Declaration of a variable num2 
    num2 = 50;  // Assignment 
    System.out.println(num2);// ww w  .j av  a2s.c o  m
  }
}

Result

Initialization

The following code declares an int variable num3 and initializes it to a value 100:

int num3 = 100; // Declaration of variable num3 and its initialization 

Demo

public class Main {
  public static void main(String[] args) {
    int num3 = 100; // Declaration of variable num3 and its initialization 
    System.out.println(num3);//from   ww  w.  ja  v a  2  s. c  o  m
  }
}

Result

Declare more than variables

To declare more than one variable of the same type in one declaration, separate each variable name by a comma.

  
// Declaration of three variables num1, num2 and num3 of type int 
int num1, num2, num3; 

To declare more than one variable in one declaration, and initialize some or all.

Declaration of variables num1, num2 and num3. Initialization of only num1 and num3

int num1 = 10, num2, num3 = 20; 
  

Declaration and initialization of variables num1, num2 and num3

int num1 = 10, num2 = 20, num3 = 30;