Mutator and Accessor(Using Inheritance)

Question

I want my program to input a private variable from another class.

I want to use the mutator and accessor.

It keeps erroring NullPointerException. What's the problem in my code?

public abstract class Inputs {
private String val;
private String typ;
public abstract void setVal(String val);
public abstract void setTyp(String typ);
public abstract String getVal();
public abstract String getTyp();
}

public DeckOfCards extends Inputs{
String val;
String typ;
static DeckOfCards kerds = new DeckOfCards();
    public void setVal(String val){
        this.val = val;
    }

    public void setTyp(String typ){
        this.typ = typ;
    }

    public String getVal(){
        return this.val;
    }

    public String getTyp(){
        return this.typ;
    }
    public static void main(String args[]){
       System.out.print("Value: ");
       kerds.setVal(kerds.val);
       if(kerds.val.equals("A"){
          System.out.print("Type: ");
          kerds.setTyp(kerds.typ);
       }
    }
}

The complete error in your console : http://stackoverflow.com/questions/3988788/what-is-a-stack-trace-and-how-can-i-use-it-to-debug-my-application-errors — Suresh Atta, Oct 02 '15 at 08:26

score 1 · Accepted Answer · edited May 23 '18 at 13:01

1

Here is your problem kerds.setVal(kerds.val); kerds is not created yet when main runs.

You need to initialize the instance of DeckOfCards before using it.
Only attempt to retrieve values after they are set. Else the attempt to retrieve a value that isn't yet set will throw a NullPointerException (Just as Rehman has pointed out)

Here is an example of proper usage:

     public static void main(String args[]){
        DeckOfCards kerds = new DeckOfCards();
        kerds.setVal("A");
        kerds.setTyp("TYPE_A");

        System.out.println("Displaying values of kerds");
        System.out.println("kerds value : " + kerds.getVal());
        System.out.println("kerds type : " + kerds.getTyp());
        }

edited May 23 '18 at 13:01

marc_s

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answered Oct 02 '15 at 08:24

Clyde D'Cruz

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what if the user must input it first? should i use kerds.val=input.next(); ? – Mariel Oct 02 '15 at 09:26
For getting keyboard input, please look at this: http://stackoverflow.com/questions/17538182/getting-keyboard-input – Clyde D'Cruz Oct 02 '15 at 09:30
If you have found this answer useful, you may accept it, else feel free to vote it up :) http://stackoverflow.com/help/why-vote – Clyde D'Cruz Oct 02 '15 at 09:40

score 0 · Answer 2 · answered Oct 02 '15 at 08:33

0

kerds.setVal(kerds.val) is setting a null value. At that point value of kerds.val is not set yet . Basically your code doesnt make any sense. You are setting a property with a value of same property which is not set yet.

answered Oct 02 '15 at 08:33

Rahman

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Mutator and Accessor(Using Inheritance)

2 Answers2