Q:

Methods need to return string from user.Need troubleshoot only

I'm a beginner in Java programming, I tried everything I could but I cant seems to troubleshoot my problem.
The problem Im facing is the getCardID() methods keep returning null value, the getTokenBalance() seems to work fine, or do i need special code to return a string value from getCardID()?
Any help is very much appreciate.
This is Prepaidcard.java class:
class PrepaidCard {
    private String cardID;
    private int tokenBalance;

    public PrepaidCard(String id) { // My First Constructor
        String cardID = id ;
    }

    public PrepaidCard(String id, int token) { // My Second Constructor
        String cardID = id;
        tokenBalance = token;
    }

    public void addToken(int token) { // Methods
        tokenBalance =token+tokenBalance;
    }

    public void deductToken(int token) { // Methods
        tokenBalance=tokenBalance-token;
    }

    public int getTokenBalance() { // Methods
        return tokenBalance;
    }

    public String getCardID() { // Why does this method keep returning null value?
        return cardID;
    }
}

This is the class use to test prepaidcard.java
import java.util.*;

class testprepaid {
    public static void main(String [] args) {
        Scanner sc = new Scanner(System.in);

        System.out.print("Insert card1 id : "); 
        String newid = sc.nextLine(); // my scanner class that read user input in String

        System.out.print("Insert card2 id : "); 
        String newid2 = sc.nextLine(); // my scanner class that read user input in String

        System.out.print("Enter Card2 initial token : ");
        int itoken = sc.nextInt();

        PrepaidCard card1 = new PrepaidCard(newid);   // object created base on 1st & 2nd Constructor
        PrepaidCard card2 = new PrepaidCard(newid2,itoken);

        System.out.println("Card1 ID: " + card1.getCardID());     // the method return null when called
        System.out.println("Card1 token balance : " + card1.getTokenBalance());
        System.out.println("Card2 ID: " + card2.getCardID());          // and this
        System.out.println("Card2 token balance : " + card2.getTokenBalance());

And other line contains no error so I didn't add them.
You can see my runtime error here.

A:

In your constructor, you declared a new local variable:
public PrepaidCard(String id, int token) {// My Second Constructor

    String cardID = id; //This should be cardID = id;
    tokenBalance = token;
}

Depending on your IDE, you may enable warnings that could tell you about uninitialized private members.

