Operators: arithmetic, relational, logical, bitwise

The canteen offer

What is an operator?

Words you'll meet in this lesson

All operator families

The tricky operators, up close

Shift operators

How Java evaluates an expression

Take total = price * qty + 10 > 70 && member. Java follows the same steps for any expression.

1. Group by precedence

   javac adds invisible brackets: total = (((price * qty) + 10) > 70) && member.

   This happens while parsing. The compiler builds a tree where higher-precedence operators sit lower, closer to the values.

2. Evaluate operands left to right

   Java always evaluates the left operand of a binary operator before the right one.

   Unlike C, this order is guaranteed by the Java specification, so a++ + a always gives the same result on every JVM.

3. Apply each operator

   price * qty → 60, + 10 → 70, > 70 → false.

   In bytecode this is a sequence on the operand stack: iload, iload, imul, bipush 10, iadd, then a comparison and a jump.

4. Short-circuit if possible

   The left side of && is false, so member is never read.

   javac compiles && into a conditional jump: if the left side is false, jump straight past the right side.

5. Assign the result

   The final value goes into total. Assignment has the lowest precedence and works right to left: a = b = 5 sets b first, then a.

   An assignment is itself an expression whose value is the assigned value. That's why if (x = 5) is a type error in Java: the result is an int, not a boolean.

Six operator surprises: both views

Left: the code and what prints. Right: the order of evaluation and the bits.

Operators in real systems

Operators look like school maths, but in production code they do some clever jobs.

Watch it with an example: checkout rules at an online store

Cart total Rs 850, the customer is a member. Watch each operator do its job, in the order Java evaluates them.

Examples are simplified to show where operators fit. Real implementations vary.

Riya's canteen bill

public class Main {
    public static void main(String[] args) {
        int price = 20, qty = 3;
        int total = price * qty + 10;          // * before +
        total += total / 10;                   // add 10% tax
        int a = 5;
        int b = a++ + ++a;                     // 5 + 7
        boolean member = total > 70 && a % 2 == 1;
        String msg = member ? "Free chai!" : "No offer";
        System.out.println(total + " " + a + " " + b + " " + msg);
    }
}

• price * qty + 10Multiplication first: 60 + 10 = 70.
• total += total / 10;Compound assignment: 70 + 7 = 77 (integer division).
• a++ + ++aUses 5, then a becomes 6; then a becomes 7 and 7 is used. b = 12.
• total > 70 && a % 2 == 1Relational and equality operators bind tighter than &&: true && true.
• member ? … : …The ternary operator picks one of two values.

Evaluate it like the JVM

Each step shows how the expression on that line is broken down and in which order.

Worked examples: real problems, solved and traced in memory

Operators turn values into answers: arithmetic, comparison, logical, compound assignment and increment. Each program below answers a real business question with nothing but operators. Watch the variables change on the stack after each expression.

items 450, 299, 180; 10% off; delivery 40; 3 people

Bill: Rs 876
Each pays Rs 292, leftover Rs 0

2024, 1900, 2000

2024: true
1900: false
2000: true

tokens start at 101

Asha: 101, Ravi: 102
next is now 104, peek was 104

Check yourself

Quick revision

Interview and viva questions

Practice problems

Arithmetic, comparison, logical, compound and increment operators. Predict each result first. The last three are business tasks.

(none)

2 0

public class Main {
    public static void main(String[] args) {
        System.out.println(17 % 5 + " " + 20 % 5);
    }
}

42, 17

true false

public class Main {
    public static void main(String[] args) {
        System.out.println((42 % 2 == 0) + " " + (17 % 2 == 0));
    }
}

10

19

public class Main {
    public static void main(String[] args) {
        int x = 10;
        x += 5;
        x *= 3;
        x -= 7;
        x /= 2;
        System.out.println(x);
    }
}

58

PASS

public class Main {
    public static void main(String[] args) {
        int marks = 58;
        System.out.println(marks >= 40 ? "PASS" : "FAIL");
    }
}

d = 0

ok = false

public class Main {
    public static void main(String[] args) {
        int d = 0;
        boolean ok = d != 0 && 100 / d > 5;
        System.out.println("ok = " + ok);
    }
}

350, member

Free delivery: true

public class Main {
    public static void main(String[] args) {
        int cart = 350;
        boolean member = true;
        System.out.println("Free delivery: " + (cart >= 499 || member));
    }
}

2800

500 x 5
100 x 3

public class Main {
    public static void main(String[] args) {
        int amount = 2800;
        System.out.println("500 x " + amount / 500);
        System.out.println("100 x " + amount % 500 / 100);
    }
}

34, 28000

Eligible: true

public class Main {
    public static void main(String[] args) {
        int age = 34, income = 28000;
        boolean eligible = age >= 21 && age <= 60 && income >= 25000;
        System.out.println("Eligible: " + eligible);
    }
}

Real-world scenario questions (asked in company interviews)

Operator bugs hide in plain sight. Decide your answer first, then open the model answer.