Thread: Help with errors Excercise -create class program and objects.

bellow are the questions

(a) Write a complete Java class definition named PrepaidCard to model a game arcade centre‘s prepaid token card. The class information is as described below:

Class name: PrepaidCard

Attributes: private String cardID
private int tokenBalance

Constructors:public PrepaidCard(String id)
Purpose: This constructor has a parameter, which is id (type String). This constructor will instantiate this class object by assigning the parameter value to the object’s cardID attribute.

public PrepaidCard(String id, int token)
Purpose: This constructor has two parameters; id (type String) and token (type int). This constructor will instantiate this class object by assigning the parameter values to the object’s cardID and tokenBalance attributes respectively.

Member
Methods: public void addToken(int token)
Purpose: To add the value of the method parameter to the object’s tokenBalance attribute. This method will display the number of tokens successfully added.

public void deductToken(int token)
Purpose: To deduct the value of the object’s tokenBalance attribute based on the parameter value. This method should have a checking mechanism. If the value of the object’s tokenBalance is lower than the token value (parameter value) to be deducted, notify the user that the PrepaidCard object has insufficient token, else deduct the token value from the object’s tokenBalance and display the total token successfully deducted.

public String getCardID()
Purpose: To return the value of the object’s cardID.

public int getTokenBalance()
Purpose: To return the value of the object’s tokenBalance.

so this is what i did

 import java.util.Scanner;
 
		public class PrepaidCard {
			private String cardID;
			private int tokenBalance = 0;
			Scanner addToken = new Scanner(System.in);
			Scanner delToken = new Scanner(System.in);
 
 
			public PrepaidCard(String id){ //initiate class object by assigning value to id
				id = cardID;
 
 
			}
 
			public PrepaidCard(String id,int token){ //initiate class object by assigning value to id and token
				id = cardID;
				token = tokenBalance;
 
 
			}			
 
			public void addToken(int token){ //add token to balance
				System.out.println("Enter Token Addition Amount : ");
				token = addToken.nextInt();
 
				tokenBalance = tokenBalance + token;
 
				System.out.println("Total of : " + addToken + " have been deducted");
				System.out.println("Card Token Balance : " + tokenBalance);
 
			}
 
			public void deductToken(int token) { //deduct token from balance
				System.out.println("Enter Token Deduction Amount : ");
				token = delToken.nextInt();
 
				if (token < tokenBalance) {
 
				tokenBalance = tokenBalance - token;
 
				System.out.println("Total of : " + delToken + " have been deducted");
				System.out.println("Card Token Balance : " + tokenBalance);
				}
 
				else {
					System.out.println("Insufficient Token Amount");
				}
 
			}
 
			public String getcardID(){ //return cardID value
				System.out.println("Identification: " + cardID);
				return cardID;
 
 
			}
 
			public int gettokenBalance(){//return tokenBalance value
				System.out.println("Card Token Balance : " + tokenBalance);
				return tokenBalance;
 
			}
		}

(b) Write a Java application to test the PrepaidCard class. In your application, create two PrepaidCard objects named card1 and card2 using the PrepaidCard(String id) and the PrepaidCard(String id, int token) constructors respectively. Display both objects’ cardID and tokenBalance. Next, ask the user to add token for card2 and display card2 new tokenBalance value. Deduct some token values from card2 and display the card2 new tokenBalance. Finally, deduct a much higher token value from the card2 current tokenBalance to test the checking mechanism of the tokenBalance value. You may use the Scanner class to read the input from user. A sample of the program execution is given below for your reference:

Enter Card1 cardID: A123
Enter Card2 cardID: B456
Enter Card2 initial token: 100
Card1 ID: A123
Card1 token balance: 0
Card2 ID: B456
Card2 token balance: 100
Enter total token to be added into Card2: 50
Total of 50 tokens added
Card2 token balance: 150
Enter total token to be deducted from Card2: 80
Total of 80 tokens deducted
Card2 token balance: 70
Enter total token to be deducted from Card2: 100
Insufficient token. Please top-up
Card2 token balance: 70

This is what i did

import java.util.Scanner;
import java.io.*;
 
public class ApplicationPrepaidCard {
 
	public static void main(String[] args) throws IOException {
 
 
		Scanner initialToken = new Scanner(System.in);
 
 
		Scanner readID = new Scanner(System.in);
		System.out.println("Enter Card1 Identification : ");//enter card1
		String id = readID.nextLine();
 
		PrepaidCard card1 = new PrepaidCard(id);
 
		System.out.println("Enter Card2 Identification : ");//enter card2
		String id = readID.nextLine();
		System.out.println("Enter Card2 Initial Token : ");//enter initial 
		int token = initialToken.nextInt();
 
		PrepaidCard card2 = new PrepaidCard(id,token);
 
 
 
		card1.getcardID();		
 
		card1.gettokenBalance();
 
		card2.getcardID();
 
		card2.gettokenBalance();
 
		card2.addToken();
 
		card2.delToken();
 
		card2.delToken();
 
 
 
 
	}
 
}

i have errors at


1) Duplicate local variable id ()

String id = readID.nextLine();

2) The method addToken(int) in the type PrepaidCard is not applicable for the arguments ()

card2.addToken();
 
card2.delToken();
 
card2.delToken();

i am stuck and i don't know what to do next...

Originally Posted by Norm

There can only be one variable with each name. The compiler sees two variables with the name: id.
Either change the name of one of them, for example: id2
or reuse the first variable and do not define a second variable.

i am supposed to use the same id for class. but is what you mean by use id2 in object?

Originally Posted by Norm

The compiler does not find a definition for the addToken() method that has no args. It does find a definition for addToken() that takes an int value.

Either change the definition of AddToken() so it has no args
or add an int arg to the calls to the method

can you give me example of args i could do? i am actually confused.

Originally Posted by Norm

If there are two variables with the same name, change the name of one of them:

String id = something;  //  define variable: id and assign it a value
...
String id2 = somethingelse;  //define new variable: id2 (not id again) and assign it a value
 
//NOTE the following is an error because id is already defined:
String id = somethingelse;  // defines id again

is ok if i leave the class definition just like this?

import java.util.Scanner;
 
		public class PrepaidCard {
			private String cardID;
			private int tokenBalance = 0;
			Scanner addToken = new Scanner(System.in);
			Scanner delToken = new Scanner(System.in);
 
 
			public PrepaidCard(String id){ //initiate class object by assigning value to id
				id = cardID;
 
 
			}
 
			public PrepaidCard(String id,int token){ //initiate class object by assigning value to id and token
				id = cardID;
				token = tokenBalance;
 
 
			}

what i am understanding is i should change the object to as id2 but should i also make a new Scanner ? readID2???
because if i do will it not cause error to the class??

		Scanner readID = new Scanner(System.in);
		System.out.println("Enter Card1 Identification : ");//enter card1
		String id = readID.nextLine();
 
		PrepaidCard card1 = new PrepaidCard(id);
 
		System.out.println("Enter Card2 Identification : ");//enter card2
		String id2 = readID.nextLine();
		System.out.println("Enter Card2 Initial Token : ");//enter initial 
		int token = initialToken.nextInt();
 
		PrepaidCard card2 = new PrepaidCard(id,token);

Originally Posted by Norm

addToken(1234); //  pass an int arg of 1234

The actual value of the arg(instead of 1234) depends on what the addToken() method requires. You would need to look at the method to see what value it needs passed to it as an arg.

is it possible to put the arg value base on the key in from scanner? because i already did at the class.

}			
 
			public void addToken(int token){ //add token to balance
				System.out.println("Enter Token Addition Amount : ");
				token = addToken.nextInt();
 
				tokenBalance = tokenBalance + token;
 
				System.out.println("Total of : " + addToken + " have been deducted");
				System.out.println("Card Token Balance : " + tokenBalance);
 
			}
 
			public void deductToken(int token) { //deduct token from balance
				System.out.println("Enter Token Deduction Amount : ");
				token = delToken.nextInt();
 
				if (token < tokenBalance) {
 
				tokenBalance = tokenBalance - token;
 
				System.out.println("Total of : " + delToken + " have been deducted");
				System.out.println("Card Token Balance : " + tokenBalance);
				}
 
				else {
					System.out.println("Insufficient Token Amount");
				}

--- Update ---

this might help.. this is the question..

PURPOSE
To create class program and its objects

REQUIREMENT
(a) Write a complete Java class definition named PrepaidCard to model a game arcade centre‘s prepaid token card. The class information is as described below:

Class name: PrepaidCard

Attributes: private String cardID
private int tokenBalance

Constructors: public PrepaidCard(String id)
Purpose: This constructor has a parameter, which is id (type String). This constructor will instantiate this class object by assigning the parameter value to the object’s cardID attribute.

public PrepaidCard(String id, int token)
Purpose: This constructor has two parameters; id (type String) and token (type int). This constructor will instantiate this class object by assigning the parameter values to the object’s cardID and tokenBalance attributes respectively.

Member
Methods: public void addToken(int token)
Purpose: To add the value of the method parameter to the object’s tokenBalance attribute. This method will display the number of tokens successfully added.

public void deductToken(int token)
Purpose: To deduct the value of the object’s tokenBalance attribute based on the parameter value. This method should have a checking mechanism. If the value of the object’s tokenBalance is lower than the token value (parameter value) to be deducted, notify the user that the PrepaidCard object has insufficient token, else deduct the token value from the object’s tokenBalance and display the total token successfully deducted.

public String getCardID()
Purpose: To return the value of the object’s cardID.

public int getTokenBalance()
Purpose: To return the value of the object’s tokenBalance.







(b) Write a Java application to test the PrepaidCard class. In your application, create two PrepaidCard objects named card1 and card2 using the PrepaidCard(String id) and the PrepaidCard(String id, int token) constructors respectively. Display both objects’ cardID and tokenBalance. Next, ask the user to add token for card2 and display card2 new tokenBalance value. Deduct some token values from card2 and display the card2 new tokenBalance. Finally, deduct a much higher token value from the card2 current tokenBalance to test the checking mechanism of the tokenBalance value. You may use the Scanner class to read the input from user. A sample of the program execution is given below for your reference:

Enter Card1 cardID: A123
Enter Card2 cardID: B456
Enter Card2 initial token: 100
Card1 ID: A123
Card1 token balance: 0
Card2 ID: B456
Card2 token balance: 100
Enter total token to be added into Card2: 50
Total of 50 tokens added
Card2 token balance: 150
Enter total token to be deducted from Card2: 80
Total of 80 tokens deducted
Card2 token balance: 70
Enter total token to be deducted from Card2: 100
Insufficient token. Please top-up
Card2 token balance: 70

i am so sorry i am at the beginner level so i might be asking silly questions because i don't understand what you mean.

Originally Posted by Norm

Is that what the assignment says to do?

That says to pass an int value as an arg

About the variable: id
You can use it more than one time
or you can define a new variable (like id2) and use that the next time.
It's up to you

PrepaidCard(String id)
Purpose: This constructor has a parameter, which is id (type String). This constructor will instantiate this class object by assigning the parameter value to the object’s cardID attribute.

public PrepaidCard(String id, int token)
Purpose: This constructor has two parameters; id (type String) and token (type int). This constructor will instantiate this class object by assigning the parameter values to the object’s cardID and tokenBalance attributes respectively.

because we have learn about overload constructor but we were not told on how to use it. so i am guessing that that might be what the assignment wants us to use in order to approach to the purpose.

so if i were to use both id as id. and then on object to let user input both the value of the id, how should i do it?
is there any example?

Originally Posted by Norm

That says to pass an int value as an arg

It's up to you

and for the arg. if i set the arguments to let say
addToken(1234) will my scanner works later??