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boolean

Learn true/false values with boolean.

What is boolean?

boolean is a type that can take only two values: true and false. It is used for logical decisions and flags.

boolean active = true;
boolean ready = false;

A boolean variable usually holds the result of a condition. For example userInput > 0 produces true or false.

Boolean values are written without quotes. "true" is a String, while true is a boolean.

Practice Define a boolean and print it

Write a Main class with a main method. Assign true to boolean active. Print it with println.

Sample solution

Main.java
public class Main {
    public static void main(String[] args) {
        boolean active = true;
        System.out.println(active);
    }
}

Expected output

true

What is boolean used for?

Boolean variables are usually flags that steer the program flow. They hold whether a feature is on/off, whether a user is signed in, or whether a file exists.

An if condition expects a boolean inside its parentheses:

boolean signedIn = true;
if (signedIn) {
    System.out.println("Welcome");
}

That is why comparisons (>, ==) produce a boolean.

Questions and answers

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

1 Match the boolean concepts

Term Meaning
true True
false False
boolean Logical type
! Not
&& And

2 Which is a valid boolean value?

  • 42
  • true Correct answer
  • "yes"
  • 1

Explanation: boolean can only be true or false.

3 Assign a value to a boolean variable

Question 
boolean active = ____;
Answer 
boolean active = true;

Explanation: A boolean is written without quotes as true or false.

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