polymorphism in java

[Tobi Taiwo]

please help with this i access methods of class A in class B and then i access class variable of class B in Class A but its giving a runtime error. note that both were done using java polymorphism attribute

[Knute Snortum]

Welcome to the Ranch.

Could you post some working code? And when you do, remember to use code tags.

[Tobi Taiwo]

what is the code tag as am new to this

[Knute Snortum]

They are a way to format your code on your posts.

[Jesper de Jong]

Welcome to the Ranch. The following page explains code tags: Use Code Tags. You should use them so that the forum can display your source code nicely formatted.

And Knute is right, your question is really hard to answer without seeing your source code. What do you mean with "Java polymorphism attribute"?

[Tobi Taiwo]

okay, this is just an example,

Public class a{
Public int acc=20;
With shell = new With();
Public static void main(String [] args){
shell.solve();
System.out.println("example");
}
}
Public class With{
Int sol;
Int net = 56;
A cat = new A();
Public void solve(){
sol = cat.acc + net;
System.out.println(sol);
}
}

when i run this it gives me an error but doesn't show an error before, i mean it shows a runtime error saying hashmap or something and also i could have put the acc inside the solve method but i choose this way as dis is an example

[Knute Snortum]

That's not working code. Get rid of the errors and post the code in another message (don't edit the original).

Remember that Java is cAsE sEnSiTiVe.

[Joanne Neal]

 

Tobi Taiwo wrote:it shows a runtime error saying hashmap or something

Don't paraphrase. Copy and paste the exact error message - they usually provide a lot of useful information for debugging problems.

[Tobi Taiwo]

sorry i just use that as an example not caring about the case sensitivity
this is the second

package atm;
public class Withdrawal {
private Keypad atmKeypad = new Keypad();
private Screen atmScreen = new Screen();
BankDatabase bankDatabase = new BankDatabase();
private double amountInput;
private double requestedMoney;
public void withdrawalMoney(){
atmScreen.displayMessage("Please Enter the Amount");
amountInput = atmKeypad.getInput();
validateWithdrawal();
}
private void validateWithdrawal(){
if (amountInput<= bankDatabase.availableBalance){
requestedMoney = amountInput;
}
else{
atmScreen.displayMessageLine("Insufficient Fund");
System.out.println(bankDatabase.availableBalance);
//System.exit(0);
}
}
}

this is the second

package atm;
public class BankDatabase {
private Screen atmScreen = new Screen();
private Keypad atmKeypad = new Keypad();
private Withdrawal userWithdrawal = new Withdrawal();
private int accountNumber;
private int accountPin;
public double availableBalance;
private double totalBalance;
public int menuInput;
public void acount(){
accountNumber = 1234567890;
accountPin = 1234;
availableBalance = 10000.50;
totalBalance = 10000.50;
}
public void authenticateUser(int account, int pin){
System.out.println(account + "" + pin);
if ((account == accountNumber)&&(pin == accountPin)){
atmScreen.displayMenu();
menuInput = atmKeypad.getInput();
switch(menuInput){
case(1):
userWithdrawal.withdrawalMoney();
case(2):
//BalanceInquiry();
case(3):
//Deposit();
case(4):
System.exit(0);
default:
atmScreen.displayMessage("You entered an invalid menu and the program is exiting");
System.exit(0);
}
}
else{
atmScreen.displayMessageLine("\nYour Account Number or Pin is incorrect\nPlease try again or exit the ATM\n");
}
}
}

this is the rest

package atm;
public class ATM {
private Screen atmScreen = new Screen();
private Keypad atmKeypad = new Keypad();
private BankDatabase bankDatabase = new BankDatabase();
private boolean access = false;
private int accountNumber;
private int accountPin;
public void run(){
while (!access){
atmScreen.displayMessageLine("Welcome to CHECK BANK ATM");
atmScreen.displayMessage("Please Enter your Account Number: ");
accountNumber = atmKeypad.getInput();
atmScreen.displayMessage("Please Enter your Pin: ");
accountPin = atmKeypad.getInput();
bankDatabase.authenticateUser(accountNumber, accountPin);
}
}
}

as i said its unfinish
this are the rest

package atm;
public class Screen {
public void displayMessage(String message){
System.out.print(message);
}
public void displayMessageLine(String message){
System.out.println(message);
}
public void displayMenu(){
System.out.println("(1) Withdrawal (2) Balance Inquiry (3) Deposit (4) Exit");
}
}

and also

package atm;
public class ATMRun {
public static void main(String [] args){
ATM bankATM = new ATM();
bankATM.run();
}
}

lastly

package atm;
import java.util.Scanner;
public class Keypad {
private Scanner input;
public Keypad(){
input = new Scanner(System.in);
}
public int getInput(){
return input.nextInt();
}
}

[Tobi Taiwo]

remember its not finish and the problem is with withrawal and bankdatabase when i run it, it gives error

[Knute Snortum]

So with this code, what is the question?

[Tobi Taiwo]

i'm getting error when i run it, i think the problem have to do with Bankdatabase calling withrawal and then again withdrawal call Bankdatabase.
how do i solve this as both depend on each other

[Knute Snortum]

And what is the error you're getting? Remember, specific and post any stack traces or error messages.

[Tobi Taiwo]

this is the error

Exception in thread "main" java.lang.StackOverflowError
at sun.nio.cs.SingleByte$Decoder.implReplaceWith(Unknown Source)
at java.nio.charset.CharsetDecoder.replaceWith(Unknown Source)
at java.nio.charset.CharsetDecoder.<init>(Unknown Source)
at java.nio.charset.CharsetDecoder.<init>(Unknown Source)
at sun.nio.cs.SingleByte$Decoder.<init>(Unknown Source)
at sun.nio.cs.MS1252.newDecoder(Unknown Source)
at sun.nio.cs.StreamDecoder.<init>(Unknown Source)
at sun.nio.cs.StreamDecoder.forInputStreamReader(Unknown Source)
at java.io.InputStreamReader.<init>(Unknown Source)
at java.util.Scanner.<init>(Unknown Source)
at atm.Keypad.<init>(Keypad.java:8)
at atm.Withdrawal.<init>(Withdrawal.java:4)
at atm.BankDatabase.<init>(BankDatabase.java:6)
at atm.Withdrawal.<init>(Withdrawal.java:6)
at atm.BankDatabase.<init>(BankDatabase.java:6)
at atm.Withdrawal.<init>(Withdrawal.java:6)
at atm.BankDatabase.<init>(BankDatabase.java:6)
at atm.Withdrawal.<init>(Withdrawal.java:6)
at atm.BankDatabase.<init>(BankDatabase.java:6)

[Paweł Baczyński]

Your BankDatabase is creating a new instance of Withdrawal which is creating a new instance of BankDatabase which is creating a new instance of Withdrawal which is creating a new instance of BankDatabase which is creating a new instance of Withdrawal which is creating a new instance of BankDatabase which is creating a new instance of Withdrawal which is creating a new instance of BankDatabase which is creating a new instance of Withdrawal which is creating a new instance of BankDatabase which is creating a new instance of Withdrawal which is creating a new instance of BankDatabase which is....
And so on and so on until the stack explodes.

[Tobi Taiwo]

so, what do i do

[Paweł Baczyński]

You need to rethink your design.
I doubt bank database needs an instance of withrawal as a member.
I also doubt a withdrawal needs an instance of bank database. Or keypad. Or screen.

[Rico Felix]

Quickly glancing at the last set of code snippets that you've posted explains all of your problems... You have a system that was not properly designed

Its architecture is tightly coupled and the components are of low cohesion... I suggest you scrap the whole thing and start from scratch instead of trying to fix it...

One thing that is quick to notice is the fall through statements in the switch construct...

Next you are creating objects that merely perform a desired action, therefore they don't qualify to be instantiated... They contain no state attributes... These can be transformed into utility components by making there methods static

public class Keypad
{
public static int getInput()
{
try
{
return Integer.parseInt(System.console().readLine());
}
catch (NumberFormatException nfe)
{
System.out.println("Invalid input");
}
return 0;
}
}

Now it can be used like -> int menuInput = Keypad.getInput();

Overall, redesign your system without thinking about programming syntax and focus on the interaction between the components of the system... Make each component perform one specific task and you should end up with better results...

[Tobi Taiwo]

thanks