Numbers & Arithmetic Operators

In Plain English

Java provides standard arithmetic operators along with a powerful built-in Math library for advanced calculations. Understanding integer division and operator precedence prevents subtle math bugs.

The Mental Model

"Integer division in Java is like cutting whole apples. If you divide 7 apples among 2 people, each gets 3 whole apples—the fractional half is discarded unless you use double!"

Deep Dive: How It Works

Basic operators: `+` (add), `-` (subtract), `*` (multiply), `/` (divide), `%` (modulus / remainder).

Integer Division Trap: Dividing two integers (e.g. `5 / 2`) produces an integer (`2`), truncating the decimal. To get `2.5`, at least one operand must be a floating point (`5.0 / 2`).

Compound operators: `+=`, `-=`, `*=`, `/=`, `%=`, `++` (increment), `--` (decrement).

Math utility class: `Math.max(a, b)`, `Math.min(a, b)`, `Math.sqrt(x)`, `Math.pow(base, exp)`, `Math.abs(x)`.

Syntax Blueprint

int sum = a + b;
int remainder = a % b;
double root = Math.sqrt(25.0);

Use % to find remainders (useful for even/odd checks). Use Math methods for powers and roots.

Core Rules to Remember

Modulus Operator %: Returns remainder: 10 % 3 equals 1.

Integer Division: 7 / 2 yields 3; 7.0 / 2 yields 3.5.

Math Library: Built into java.lang—no import needed.

Common Beginner Traps & How to Fix Them

Mistake:Expecting a decimal from int division: double d = 5 / 2; (results in 2.0)

Why it happens: 5 / 2 evaluates to 2 as an int, which is then cast to 2.0.

How to fix: Write double d = 5.0 / 2; or (double) 5 / 2;

Pro Tip: Use n % 2 == 0 to check if any integer n is even.

Live Interactive Example

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Arithmetic and Math Functions

Java 13

Output Console

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How it works: Notice how 14 / 4 gives 3, but 14.0 / 4 gives 3.5. Math.pow returns a double.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Calculate rectangle area and perimeter

Given length = 8 and width = 5, calculate area (length * width) and perimeter (2 * (length + width)).
Print "Area: " + area and "Perimeter: " + perimeter on separate lines.

Sandbox Output

Click "Run & Check" to test your solution.

Finished reading and practicing?

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Deep Dive: How It Works

Basic operators: `+` (add), `-` (subtract), `*` (multiply), `/` (divide), `%` (modulus / remainder).

Integer Division Trap: Dividing two integers (e.g. `5 / 2`) produces an integer (`2`), truncating the decimal. To get `2.5`, at least one operand must be a floating point (`5.0 / 2`).

Compound operators: `+=`, `-=`, `*=`, `/=`, `%=`, `++` (increment), `--` (decrement).

Math utility class: `Math.max(a, b)`, `Math.min(a, b)`, `Math.sqrt(x)`, `Math.pow(base, exp)`, `Math.abs(x)`.