Question

I have a class called ‘Items’ to which ‘Equips’ extends from and ‘Helmet’ then extends from ‘Equips’. I have a method called ‘getStats’ that loads the item’s stats from a .txt file. If I put the ‘getStats’ method in the ‘Items’ class, whatever field I try to access in a ‘Helmet’ object using ‘this.’ shows up null. The field I’m trying to access in ‘Helmet’ is initialized when the helmet is created before the text file is loaded. I could very easily just put the ‘getStats’ method in the ‘Equips’ class and put a blank ‘getStats’ method in the ‘Items’ class, but I was wondering if there was a way to make it work how it is. Thanks in advance!

Items.java:

package com.projects.aoa;

import static com.projects.aoa.Print.*;

import java.util.*;
import java.io.*;

class Items {

String name, type;
int id;
int hp, mp, str, def;
boolean vacent;

static void getAllStats(Items[] e){
    for(Items i : e){
        getItemStats(i);
    }
}

static void getItemStats(Items i){
    i.getStats();
}

void getStats(){
    try {
        //System.out.println(System.getProperty("user.dir"));

        print(this.name); //THIS shows up as null as well as those \/below\/
        FileInputStream fstream = new FileInputStream(System.getProperty("user.dir") 
                + "/src/com/projects/aoa/" + this.type + this.name + ".txt");

        DataInputStream in = new DataInputStream(fstream);

        BufferedReader br = new BufferedReader(new InputStreamReader(in));

        String line;
        int counter = 0;

        while ((line = br.readLine()) != null) {
            if (line.length() == 0){
                break;
            }

            switch (counter) {
            case 0:
                this.hp = Integer.parseInt(line);
                counter++;
                break;
            case 1:
                this.mp = Integer.parseInt(line);
                counter++;
                break;
            case 2:
                this.def = Integer.parseInt(line);
                counter++;
                break;
            case 3:
                this.str = Integer.parseInt(line);
                counter++;
                break;
            }   
        }


        in.close();
    } catch (Exception e) {
        e.printStackTrace();
    } 
}

Game.java:

Helmet headBand = new Helmet("HeadBand");
Helmet bronzeHelmet = new Helmet("BronzeHelmet");


    Items[] equips = {
            headBand, bronzeHelmet
    };



    getAllStats(equips);

Equips.java:

  package com.projects.aoa;

import static com.projects.aoa.Print.print;
import static com.projects.aoa.Print.println;

import java.io.*;



class Equips extends Items{
    String name, type;
    int hp, mp, str, def;




    void printStats(){
        println("[" + name + "]");
        println("Type: " + type);
        println("HP:  " + hp);
        println("MP:  " + mp);
        println("Def: " + def);
        println("Str: " + str);
    }
}

class Helmet extends Equips {
    Helmet(String name){
        this.name = name;
        this.type = "h_";
    }
}

Answer 1

You haven’t shown us your Helmet class, so it’s hard to say what’s going on – but my guess is that you’re redeclaring fields with the same name in Helmet. Those will hide the fields in Items, whereas you really just want to use the fields from Items.

So here’s a short but complete example which demonstrates what I think is going on:

class SuperClass {
    String name;

    public void setName(String newName) {
        // This writes to the field in SuperClass
        name = newName;
    }
}

class SubClass extends SuperClass {
    // This *hides* the field in SuperClass
    String name;

    public void showName() {
        // This reads the field from SubClass, which
        // nothing writes to...
        System.out.println("My name is " + name);
    }
}

public class Test {
    public static void main(String[] args) {
        SubClass x = new SubClass();
        x.setName("Test");
        x.showName();
    }
}

I would recommend that:

• You make all fields private, writing properties to give access to other classes as required
• You get rid of the fields in Helmet which hide the ones in Items
• You change your class names to avoid the plurality – Item and Equipment instead of Items

Here’s a fixed version of the above code:

class SuperClass {
    private String name;

    public void setName(String newName) {
        name = newName;
    }

    public String getName() {
        return name;
    }
}

class SubClass extends SuperClass {
    public void showName() {
        System.out.println("My name is " + getName());
    }
}

public class Test {
    public static void main(String[] args) {
        SubClass x = new SubClass();
        x.setName("Test");
        x.showName();
    }
}

(Obviously you also need to think about what access to put on the properties etc, but that’s a separate matter.)