ComplexNumber.java

final class ComplexNumber {
    private float realPart;
    private float complexPart;

    // create a new instance via static method
    public static ComplexNumber zero() {
        return new ComplexNumber(0, 0);
    }

    // create a new instance via constructor
    public ComplexNumber(float realPart, float complexPart) {
        this.realPart = realPart;
        this.complexPart = complexPart;
    }

    // create a new ComplexNumber by addition
    public ComplexNumber add(ComplexNumber anotherComplexNumber) {
        return new ComplexNumber(
                realPart + anotherComplexNumber.realPart,
                complexPart + anotherComplexNumber.complexPart
        );
    }

    // extract internal data and convert to String
    public String toString() {
        return String.format("%f + %f i", realPart, complexPart);
    }
}