coding OOP skema Inheritance

package oop;
class manusia{
    private String nama;
    manusia(){
    }
    void aku_petrus (String c){
        nama = c;
    }
    void get_petrus(String c){
        nama = c;
    }
    void get_petrus(){
        System.out.println("nama - " + nama);
    }
}
class mahasiswa extends manusia{
    private int npm;
    private double ipk;
   mahasiswa(){
    }
    void nyo_aku (int id, double ip){
        npm = id;
        ipk = ip;
    }
    void get_nyo_aku (int id, double ip){
        npm = id;
        ipk = ip;
    }
    void get_who(){
       System.out.println("NPM - "+npm);
       System.out.println("IPK - "+ipk);
    }
}
    class pekerja extends mahasiswa {
        private int id;
        private String gaji;
        pekerja(){

        }
        void petrus_kane(int a, String s){
            id = a;
            gaji = s;
        }
        void get_petrus_kane(int a, String s){
            id = a;
            gaji = s;
        }
        void get_petrus_kane(){
            System.out.println("id - " +id);
            System.out.println("gaji - "+gaji);
        }
    }
public class Main {
 public static void main(String[] args) {
       manusia tra = new manusia ();
       tra.aku_petrus("PETRUS");
       tra.get_petrus();
       mahasiswa mm = new mahasiswa ();
       mm.get_nyo_aku(1135010005, 3.70);
       mm.get_who();
       pekerja plang = new pekerja ();
       plang.get_petrus_kane(0024, "6.000.000");
       plang.get_petrus_kane();
 }
}



OUTPUT:
nama - petrus
NPM - 1135010005
IPK - 3.7
id - 05
gaji - 6.000.000
BUILD SUCCESSFUL (total time: 0 seconds)