Java: Somehow I managed to extend a final method

The Vector3 class contains this:

public final boolean set(float x, float y, float z) {
    setX(x);
    setY(y);
    setZ(z);
    return true;
}

The Vector4 class contains this:

public boolean set(float x, float y, float z, float w) {
    setX(x);
    setY(y);
    setZ(z);
    setW(w);
    return true;
}

No errors. Why?