Chapter 7: Operators in Java

This chapter is only about operators: symbols that combine values, compare them, assign results, or change variables in place. We assume you know variables and basic types from Chapters 5 and 6.

1. Topic title

Operators in Java: arithmetic, assignment, comparison, logical, ++/--, ternary, and bitwise basics

2. What it means

An operator works on one or more operands and produces a result (or performs an assignment as a side effect).

Examples:

• a + b — binary + on two numbers (or string concatenation if the left operand is String—watch that).
• !flag — unary logical NOT on a boolean.
• x += 1 — compound assignment, same idea as x = x + 1 with subtle typing rules.

3. Why it is used

Almost every program computes and decides: totals, discounts, permissions, loop steps. Operators are the low-level vocabulary for those actions. Reading them fluently is how you stop freezing on one line of someone else’s code.

4. Real-world example

A login form might combine checks:

• Password length at least 8 → comparison operators.
• Account not locked → boolean with &&.
• Optional “remember me” → || with other rules.

The business rules read as conditions built from operators (Chapter 10+ will put those inside if).

5. Java code example

public class OperatorsDemo {
    public static void main(String[] args) {
        int a = 7;
        int b = 3;
 
        System.out.println("a + b = " + (a + b));
        System.out.println("a - b = " + (a - b));
        System.out.println("a * b = " + (a * b));
        System.out.println("a / b = " + (a / b));
        System.out.println("a % b = " + (a % b));
 
        int x = 5;
        x += 2;
        System.out.println("after x += 2, x = " + x);
 
        boolean p = true;
        boolean q = false;
        System.out.println("p && q = " + (p && q));
        System.out.println("p || q = " + (p || q));
        System.out.println("!p = " + (!p));
 
        int n = 0;
        System.out.println("n++ prints " + (n++) + " then n is " + n);
        System.out.println("++n prints " + (++n) + " then n is " + n);
 
        int age = 20;
        String label = age >= 18 ? "adult" : "minor";
        System.out.println("label = " + label);
 
        int bitmask = 0b1100;
        int mask = 0b1010;
        System.out.println("bitwise AND: " + (bitmask & mask));
        System.out.println("bitwise OR: " + (bitmask | mask));
        System.out.println("bitwise XOR: " + (bitmask ^ mask));
    }
}

Output (truncated logic): integer division 7 / 3 is 2 (drops fraction—use double if you need decimals).

6. Explanation of code

Arithmetic: + - * / % on numbers. % is remainder—handy for “every third item” patterns.

Integer division: both operands int → result is int, truncated toward zero. Common surprise for beginners.

Assignment: = assigns. +=, -=, *=, /=, %= compound with the current variable value.

Comparison: == != < > <= >= produce boolean. For objects, == compares references, not deep content—use .equals for String content.

Logical: && AND, || OR, ! NOT. && and || short-circuit: the right side may not run if the answer is already decided (false && ..., true || ...).

Increment:

• n++ post-increment: use old value in the expression, then add one.
• ++n pre-increment: add one first, then use new value.

Ternary: condition ? valueIfTrue : valueIfFalse — compact if-like expression. Do not nest five levels deep; readability dies.

Bitwise: & | ^ ~ << >> >>> work on integer bits. You see them in low-level IO, flags, and performance code. Learn & | ^ first; shifts when a tutorial needs them.

7. Common mistakes

Using = in a condition by accident when you meant ==:

if (x = 5) { } // compile error in Java for boolean context — good guard

Mixing && vs & for booleans. && short-circuits; & on booleans does not short-circuit. For logic, almost always use && and ||.

String concatenation surprise:

System.out.println("Sum: " + 1 + 2); // prints Sum: 12

Left operand is String, so + means concat. Use parentheses: "Sum: " + (1 + 2).

Over-clever ternary spanning three lines—just use if.

8. Best practices

Use parentheses when mixing types of operators so readers do not parse precedence in their heads.

Prefer meaningful names over magic: isEligible = age >= 18 && hasConsent beats a pile of literals in one return.

Know integer division before you debug “wrong average” bugs.

Reach for BigDecimal for money math, not double tricks—when you build real billing.

9. Small practice task

Given int minutes = 125, compute full hours and remaining minutes using / and %, print both. Then set minutes to 59 and run again. No floats needed.

Beginner tip

Precedence tables are boring to memorize. When in doubt, add parentheses. No prize for minimal parentheses in learning code.