CodeBlanks Logo Icon CodeBlanks
Login Register

Logical

Learn boolean logic with &&, ||, !.

Logical operators

Logical operators combine boolean values: && (and), || (or), ! (not).

boolean a = true;
boolean b = false;
System.out.println(a && b); // false
System.out.println(a || b); // true
System.out.println(!a);     // false

&& returns true only if both sides are true. || returns true if at least one side is true. ! flips the value.

&& and || short-circuit: if the left side already decides the result, the right side is not evaluated. This prevents possible errors.

Short-circuit behavior

The && and || operators short-circuit. If the left side already decides the result, the right side is not evaluated.

if (b != 0 && a / b > 1) { ... }

Here, if b == 0, && makes the left side false and the right side (a / b) is not evaluated. This avoids a division by zero.

The bitwise & and | do not short-circuit; they evaluate both sides. For logic, && and || are preferred.

Practice Print with logical operators

Write a Main class with a main method. Assign 20 to int age. Print age >= 18 && age <= 65 with println.

Sample solution

Main.java
public class Main {
    public static void main(String[] args) {
        int age = 20;
        System.out.println(age >= 18 && age <= 65);
    }
}

Expected output

true

Questions and answers

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

1 Complete the logical and operator

Question 
boolean result = true ____ false;
Answer 
boolean result = true && false;

Explanation: The and operator is &&.

2 Match the logical operators

Term Meaning
&& And
|| Or
! Not
true True

3 What is the result of true || false?

  • false
  • true Correct answer
  • 1
  • 0

Explanation: || returns true if at least one side is true.

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