// This is the call of the method, giving two objects

    addRek(wurzel, blatt);

// This is the important part
public void addRek(Blatt refer, Blatt blatt) {

    refer = blatt;
    // What I originally intended to do was to write the reference to 'blatt' into 'wurzel'.
    // What he does, however, is write the reference into 'refer', which is obviously lost after the method ends
    // What I need is a way to access the variable behind refer

}

// This is of course not the whole class, and I could rewrite it so this problem doesn't present itself, but if there is a way of doing it'd, that'd be nice.