Java Day 3: Operators and Expressions

Goal of this Day

Today you will learn:

• Arithmetic operators
• Assignment operators
• Comparison operators
• Logical operators

By the end, you will be able to perform calculations and make decisions in Java.

Step 1: Arithmetic Operators

Arithmetic operators are used to perform calculations.

• + → addition
• - → subtraction
• * → multiplication
• / → division
• % → remainder (modulo)

Example:

int a = 10;
int b = 3;

System.out.println("Sum: " + (a + b));
System.out.println("Remainder: " + (a % b));

Step 2: Assignment Operators

Assignment operators are used to assign values to variables.

• = → assign value
• += → add and assign
• -= → subtract and assign
• *= → multiply and assign
• /= → divide and assign

Example:

int x = 5;
x += 3;  // x is now 8

Step 3: Comparison Operators

These operators compare values.

• == → equal
• != → not equal
• > → greater than
• < → less than
• >= → greater or equal
• <= → less or equal

Example:

int age = 18;

if (age >= 18) {
    System.out.println("You are an adult");
}

Step 4: Logical Operators

Logical operators combine conditions.

&& (AND)

Both conditions must be true.

if (age >= 18 && age < 65) {
    System.out.println("Working age");
}

|| (OR)

At least one condition must be true.

if (age < 18 || age > 65) {
    System.out.println("Not typical working age");
}

! (NOT)

Reverses a condition.

boolean isStudent = false;

if (!isStudent) {
    System.out.println("Not a student");
}

Practice

int a = 10;
int b = 3;

System.out.println("Sum: " + (a + b));
System.out.println("Remainder: " + (a % b));

Exercise

Write a program that checks if a number is even or odd.

Steps:

• Create a variable for a number
• Use the modulo operator %
• If the remainder is 0 → even
• Otherwise → odd

Example:

public class EvenOdd {
    public static void main(String[] args) {
        int number = 7;

        if (number % 2 == 0) {
            System.out.println("The number is even");
        } else {
            System.out.println("The number is odd");
        }
    }
}