What is a Constant in Java

What is a Constant in Java

Overview There are several values in the real world which will never change. Sometimes we may need to define some values as constants ... August 07, 2017

Overview

• There are several values in the real world which will never change.
• Sometimes we may need to define some values as constants in our program.  
• Nobody should be able to change these values and it should be constant every time. 
• One example for a constant is the mathematical constant “pi” which has the value 3.14 every time.
• Constants in java are fixed values those are not changed during the Execution of program

Types of java Constant

• Primitive Data Types
• byte   /   short   /    int   /   long   /   float   /   double   /   boolean   /   char

• You can define any of these type variables as constants by just adding the keyword “final” when we declare the variable.

• Eg1: final int distance = 30;
• Eg2: final float pi = 3.14f;

Define a Variable as Constant

• To define a variable as constant, we just need to add the keyword “final” in front of the variable declaration.

Example 1

final int distance = 30;

• The above statement declares the int variable “distance” as a constant  with a value 30.  
• We cannot change the value of distance at any point of time in the program. 
• Later if we try to do that by using statements like “distance=40;”, Java will throw errors at compile time itself.
• It is not mandatory that you need to assign values of constants during initialization itself.

Example 2

final int distance;
distance = 30;

• Here we are first defining the int variable distance as a constant. 
• Later we are assigning the value 30 to our constant. 
• Once this value is assigned, we cannot change this value in the program and if we try to do that by using statements like “distance=40;”, Java will throw errors at compile time itself.