Java Complex Number Class with Arithmetic (partial)

public class Complex implements Comparable<Complex>, Cloneable {
    private double a; // real part
    private double b; // imaginary part

    // Constructor
    public Complex(double a, double b) {
        this.a = a;
        this.b = b;
    }

    // Getters
    public double getRealPart() { return a; }
    public double getImaginaryPart() { return b; }

    // Arithmetic operations
    public Complex add(Complex other) {
        return new Complex(this.a + other.a, this.b + other.b);
    }

    public Complex subtract(Complex other) {
        return new Complex(this.a - other.a, this.b - other.b);
    }

    public Complex multiply(Complex other) {
        double real = this.a * other.a - this.b * other.b;
        double imag = this.a * other.b + this.b * other.a;
        return new Complex(real, imag);
    }

    public Complex divide(Complex other) {
        double denominator = other.a * other.a + other.b * other.b;
        double real = (this.a * other.a + this.b * other.b) / denominator;
        double imag = (this.b * other.a - this.a * other.b) / denominator;
        return new Complex(real, imag);
    }

    // Absolute value
    public double abs() {
        return Math.sqrt(a * a + b * b);
    }

    // toString
    @Override
    public String toString() {
        if (b >= 0) return a + " + " + b + "i";
        else return a + " - " + (-b) + "i";
    }

    // equals
    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof Complex)) return false;
        Complex other = (Complex) obj;
        return this.a == other.a && this.b == other.b;
    }

    // compareTo (by absolute value)
    @Override
    public int compareTo(Complex other) {
        return Double.compare(this.abs(), other.abs());
    }

    // clone
    @Override
    public Complex clone() {
        try {
            return (Complex) super.clone();
        } catch (CloneNotSupportedException e) {
            return new Complex(this.a, this.b);
        }
    }
}