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final variables

Learn constant-value variables with final.

What is final?

The final keyword marks a variable as not reassignable. Once you give it a value, it cannot change. Such variables are called constants.

final double PI = 3.14;
PI = 3.15; // compile error

Constants are usually named in ALL_CAPS: MAX_SPEED, PI, URL. This signals to other developers that the value does not change.

Constants are ideal for values that stay the same across the program: math constants, configuration values, limits.

Practice Define a final constant and print it

Write a Main class with a main method. Assign 120 to final int MAX_SPEED. Print it with println.

Sample solution

Main.java
public class Main {
    public static void main(String[] args) {
        final int MAX_SPEED = 120;
        System.out.println(MAX_SPEED);
    }
}

Expected output

120

When to use final?

When a value will not change throughout the program, using final is good practice. It prevents accidental changes and states the intent clearly.

Common examples:

  • Math constants: PI, EULER
  • Configuration: URL, PORT
  • Limits: MAX_USERS, TIMEOUT

Local variables can also be final; variables used in lambda expressions must be effectively final.

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Match the final concepts

Term Meaning
final Constant
PI Constant example
MAX_SPEED ALL_CAPS
const Not Java

2 Complete the final constant

Question 
final double PI = ____;
Answer 
final double PI = 3.14;

Explanation: PI = 3.14 declares the math constant.

3 What can NOT be done to a final variable?

  • Reassign Correct answer
  • Print
  • Declare
  • Use

Explanation: A final variable cannot be reassigned.

All lessons in Beginner

1 Java basics

  1. What is Java?
  2. The main method
  3. Comments
  4. Class skeleton
  5. javac and java
  6. Summary - Java basics

2 Variables

  1. int and double
  2. boolean
  3. String
  4. Naming variables
  5. final variables
  6. Summary - Variables

3 Data types

  1. Primitive types
  2. Type casting
  3. String concatenation
  4. Math class
  5. BigInteger and BigDecimal
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add/subtract
  3. Multiply/divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic
  2. Comparison
  3. Logical
  4. Bitwise
  5. Assignment and increment
  6. Summary - Operators

6 String basics

  1. length and charAt
  2. equals and equalsIgnoreCase
  3. indexOf and substring
  4. toUpperCase and trim
  5. String.format
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. else and else if
  3. Nested if
  4. switch
  5. Ternary
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. do-while
  4. break and continue
  5. for-each
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Filling arrays
  4. Multi-dimensional arrays
  5. Copying arrays
  6. Summary - Arrays

11 Array methods

  1. Arrays.sort
  2. Arrays.toString
  3. Arrays.binarySearch
  4. Arrays.copyOf
  5. Arrays.fill
  6. Summary - Array methods

12 Collections

  1. ArrayList
  2. add and get
  3. HashMap
  4. put and get
  5. HashSet
  6. Summary - Collections

13 Methods

  1. Defining methods
  2. return
  3. void methods
  4. Method overloading
  5. Scope
  6. Summary - Methods

14 Method parameters

  1. Primitive parameters
  2. Object parameters
  3. varargs
  4. Multiple values via array
  5. final parameters
  6. Summary - Method parameters

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String builder

  1. StringBuilder
  2. append
  3. insert and delete
  4. reverse
  5. toString
  6. Summary - String builder

17 Input and output

  1. Scanner
  2. nextInt and nextLine
  3. System.out.printf
  4. BufferedReader
  5. try-with-resources
  6. Summary - Input and output

18 Enum

  1. Declaring enums
  2. values and valueOf
  3. Enum fields
  4. Enum methods
  5. switch with enum
  6. Summary - Enum

19 Exception basics

  1. try/catch
  2. finally
  3. throw
  4. Exception hierarchy
  5. Multiple catch
  6. Summary - Exception basics

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together