Integer Division in Java

Try It — Interactive Division Calculator

Numerator: / Denominator:

Remainder (%):

Error! Division by zero is not allowed. Java would throw an ArithmeticException.

Key Examples — Common Gotchas

Click any example to load it in the calculator above.

10 / 3 = 3

Not 3.333! — The .333 is thrown away

7 / 2 = 3

Not 3.5! — No rounding, just truncation

1 / 2 = 0

Not 0.5! — This one really surprises students

99 / 100 = 0

Not 0.99! — Anything smaller ÷ bigger = 0

10 / 5 = 2

Works fine — Divides evenly, no loss

20 / 4 = 5

Works fine — Divides evenly, no loss

Key Rule: Java does NOT round the result. It truncates — meaning it chops off everything after the decimal point. 9 / 5 gives 1, not 2.

How to Fix It — Getting the Full Decimal Result

Solution 1: Use double Variables

double num1 = 10;
double num2 = 3;
double result = num1 / num2;
System.out.println(result);
// Output: 3.3333333333333335
        

Solution 2: Type Casting

int num1 = 10;
int num2 = 3;
double result = (double) num1 / num2;
System.out.println(result);
// Output: 3.3333333333333335
        

Why does casting work? When you write (double) num1 / num2, Java converts num1 to a double first. Then, since one side is a double, Java automatically promotes the other side too. Now it is double / double, which keeps the decimal.

Common Mistake: Writing (double)(num1 / num2) does NOT work! The integer division happens first inside the parentheses (10 / 3 = 3), then you cast 3 to 3.0. The decimal is already lost.

Modulo (%) — The Remainder Integer Division Throws Away

// Integer division gives the quotient
int quotient = 10 / 3;    // 3

// Modulo gives the remainder
int remainder = 10 % 3;   // 1

// Together they tell the full story:
// 10 = 3 * 3 + 1
        

10 / 3 = 3 (quotient — how many times 3 fits into 10)

10 % 3 = 1 (remainder — what is left over)

Think of it like long division: 3 goes into 10 three times (9), with 1 left over.

Tip: The modulo operator % is very useful for checking if a number is even or odd: num % 2 == 0 means even, num % 2 != 0 means odd.