What causes "Number must be zero for E assignment!" in TheAlgorithms/Java?

Call e() on a fresh Builder (number == 0)

TheAlgorithms/Java · error · RuntimeException

Number must be zero for E assignment!

Error message

Number must be zero for E assignment!

What it means

Thrown by Builder.e() when the builder's internal number field is not 0. Same assignment-vs-accumulation pattern as pi() and rand(): e() overwrites number with Math.E and requires a clean slate. Uses RuntimeException.

Source

Thrown at src/main/java/com/thealgorithms/maths/MathBuilder.java:129

            }
            Random random = new Random();
            number = random.nextDouble(seed);
            return this;
        }

        // Takes PI value and sets to NUMBER
        public Builder pi() {
            if (number != 0) {
                throw new RuntimeException("Number must be zero for PI assignment!");
            }
            number = Math.PI;
            return this;
        }

        // Takes E value and sets to NUMBER
        public Builder e() {
            if (number != 0) {
                throw new RuntimeException("Number must be zero for E assignment!");
            }
            number = Math.E;
            return this;
        }

        public Builder randomInRange(double min, double max) {
            if (number != 0) {
                throw new RuntimeException("Number must be zero for random assignment!");
            }
            Random random = new Random();
            number = min + (max - min) * random.nextDouble();
            return this;
        }

        public Builder toDegrees() {
            if (inParenthesis) {
                sideNumber = Math.toDegrees(sideNumber);
            } else {

View on GitHub (pinned to fdfb9a395b)

Solutions

Call e() on a fresh Builder (number == 0)
Use multiply(Math.E) or add(Math.E) if you want E in an arithmetic expression
Build current state first, then start fresh for the E assignment

Example fix

// before
MathBuilder.Builder b = new MathBuilder.Builder(2).e();

// after
MathBuilder.Builder b = new MathBuilder.Builder().e();
// or for arithmetic with E:
MathBuilder.Builder b2 = new MathBuilder.Builder(2).multiply(Math.E);

Defensive patterns

Strategy: validation

Validate before calling

// Call e() only on a fresh builder
MathBuilder.Builder b = new MathBuilder.Builder();  // number == 0
b.e();

Try / catch

try {
    builder.e();
} catch (RuntimeException e) {
    builder = new MathBuilder.Builder();
    builder.e();
}

Prevention

e() overwrites number with Math.E — use multiply(Math.E) for arithmetic instead
Only call e() when number is in its initial 0 state
Do not chain e() after accumulating operations like add or multiply

When it happens

Trigger: Calling e() after any operation that left number non-zero: new MathBuilder.Builder(3).e(), or after add/multiply/set on a non-zero builder.

Common situations: Developer chains operations expecting e() to participate in arithmetic (e.g., multiply by e), but the API treats it as a raw overwrite. Confusion about builder semantics.

Related errors

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/7b1294ea097fe88b. Report an issue: GitHub.