Custom Exceptions in Java

CustomExceptions.java

package customexceptions;

public class CustomExceptions {

    public static void main(String[] args) throws NegativerWertException {
        Rechner r = new Rechner();
        try {
            double wert1 = r.rechnung1(22.2);
            System.out.println("wert1: " + wert1);
            double wert2 = r.rechnung2(-5);
            System.out.println("wert2: " + wert2);
        } catch (NegativerWertException nw) {
            System.out.println("Exception Abgefangen!");
            System.out.println("Die Variable war: " + nw.getVariablenname());
        }
    }
}

NegativerWertException.java

package customexceptions;

public class NegativerWertException extends Exception {

    private String variablenname = null;

    public NegativerWertException() {
        super("der Wert war negativ");
    }

    public NegativerWertException(String variablenname) {
        super("der Wert der Variable "
                + variablenname
                + " war negativ");
        this.variablenname = variablenname;
    }

    public String getVariablenname() {
        return variablenname;
    }
}

Rechner.java

package customexceptions;

public class Rechner {
    public double rechnung1(double x) {
        return 2*x + 1;
    }
    
    public double rechnung2(double y) throws NegativerWertException {
        if (y < 0) {
            //throw new Exception("y < 0");
            throw new NegativerWertException("y");
        }
        double z = Math.sqrt(y);
        return y - z;
    }
}