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How can i make my code be able to catch exceptions and display a incorrect input

ID: 3714369 • Letter: H

Question

How can i make my code be able to catch exceptions and display a incorrect input message if user inputs words. sample- incorrect input insert 50.0 cents for candy

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DecimalFormat;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.SwingConstants;
public class CandyMachine
extends JFrame implements ActionListener
{
  
  
   private static final long serialVersionUID = 1L;
//set constants for cost of items
   //Note : values are not given in question
   //These are assumed values .Can be change as per requirement
   private static double CANDY_COST=50;
   private static double CHIP_COST=40;
   private static double GUM_COST=30;
   private static double COOKIES_COST=20;


   private JLabel headerTop=new JLabel("WELCOME TO SHELLY'S CANDY SHOP"
           ,SwingConstants.CENTER);
   private JLabel headerBottom=new JLabel("To Make a Selection,Check the Product Price"
           ,SwingConstants.CENTER);

   private JButton candyBtn;
   private JButton chipsBtn;
   private JButton gumBtn;
   private JButton cookiesBtn;
   private JButton exitBtn;

   //constructor to intialize the frame
   public CandyMachine()
   {
       setTitle("Candy Machine");
       setSize(350, 350);
       setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       setLocationRelativeTo(null);
       setLayout(new GridLayout(7, 1));
       add(headerTop);
       add(headerBottom);
    
       //create a button and add action lister for candy button
       candyBtn=new JButton("Candy");
       candyBtn.addActionListener(this);
       add(candyBtn);

       //create a button and add action lister for chips button
       chipsBtn=new JButton("Chips");
       chipsBtn.addActionListener(this);
       add(chipsBtn);

       //create a button and add action lister for genms button
       gumBtn=new JButton("Gum");
       gumBtn.addActionListener(this);
       add(gumBtn);

       //create a button and add action lister for chocolate button
       cookiesBtn=new JButton("Cookies");
       cookiesBtn.addActionListener(this);
       add(cookiesBtn);

       //create a button and add action lister for exit button
       exitBtn=new JButton("Exit");
       exitBtn.addActionListener(this);
       add(exitBtn);
       //set visibility true
       setVisible(true);

   }
   public static void main(String[] args)
   {
       //instantiate the class
       new CandyMachine();
   }

   /**Override the actionPerformed method that handles
   * the five buttons*/
   public void actionPerformed(ActionEvent ae) {
       String item=ae.getActionCommand();
       Object obj=(JButton)ae.getSource();
       double cost=0;
       double change=0;
       DecimalFormat df=new DecimalFormat("##.00");
       //check if button is candy
       if(obj==candyBtn)
       {
           do
           {
           cost=Double.parseDouble(JOptionPane.showInputDialog(null,
                   "To buy "+item+" please insert "+CANDY_COST+" cents",
                   "Input",
                   JOptionPane.QUESTION_MESSAGE));
        
           if(cost<CANDY_COST)
               JOptionPane.showMessageDialog(null, "Not sufficient Amount");
        
           }while(cost<CANDY_COST);
        
           change=cost-CANDY_COST;
           if(change!=0)
           JOptionPane.showMessageDialog(null,
                   "Change : "+df.format(change)+" Please pick up your "+item+" and enjoy",
                   "Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);
           else
               JOptionPane.showMessageDialog(null,
                       "Please pick up your "+item+" and enjoy",
                       "Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);
       }
       //check if button is chips
       else if(obj==chipsBtn)
       {
           do
           {
           cost=Double.parseDouble(JOptionPane.showInputDialog(null,
                   "To buy "+item+" please insert "+CHIP_COST+" cents",
                   "Input",
                   JOptionPane.QUESTION_MESSAGE));
           if(cost<CHIP_COST)
               JOptionPane.showMessageDialog(null, "Not sufficient Amount");
        
           }while(cost<CHIP_COST);
        
           change=cost-CHIP_COST;
           if(change!=0)
           JOptionPane.showMessageDialog(null,
                   "Change : "+df.format(change)+" Please pick up your "+item+" and enjoy",
                   "Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);
           else
               JOptionPane.showMessageDialog(null,
                       "Please pick up your "+item+" and enjoy",
                       "Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);
       }
       //check if button is gum
       else if(obj==gumBtn)
       {
           do
           {
           cost=Double.parseDouble(JOptionPane.showInputDialog(null,
                   "To buy "+item+" please insert "+GUM_COST+" cents",
                   "Input",
                   JOptionPane.QUESTION_MESSAGE));
           if(cost<GUM_COST)
               JOptionPane.showMessageDialog(null, "Not sufficient Amount");
        
           }while(cost<GUM_COST);
        
           change=cost-GUM_COST;
        
           if(change!=0)
           JOptionPane.showMessageDialog(null,
                   "Change : "+df.format(change)+" Please pick up your "+item+" and enjoy",
                   "Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);
           else
               JOptionPane.showMessageDialog(null,
                       "Please pick up your "+item+" and enjoy",
                       "Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);
       }
       //check if button is cookies
       else if(obj==cookiesBtn)
       {
           do
           {
           cost=Double.parseDouble(JOptionPane.showInputDialog(null,
                   "To buy "+item+" please insert "+COOKIES_COST+" cents",
                   "Input",
                   JOptionPane.QUESTION_MESSAGE));
           if(cost<COOKIES_COST)
               JOptionPane.showMessageDialog(null, "Not sufficient Amount");
        
           }while(cost<COOKIES_COST);
        
           change=cost-COOKIES_COST;
           if(change!=0)
           JOptionPane.showMessageDialog(null,
                   "Change : "+df.format(change)
                   +" Please pick up your "
                   +item+" and enjoy",
                   "Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);
           else
               JOptionPane.showMessageDialog(null,
                       "Please pick up your "+item+" and enjoy",
                       "Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);
       }
       //check if button is exit
       else if(obj==exitBtn)
       {
           JOptionPane.showMessageDialog(null, "Thank you.Come again!");
           System.exit(0);
       }

   }
}

Explanation / Answer

I have modified the code to catch the exceptions when either a blank value is submitted or a non number value is entered as asked in the question.The code will throw an error . However, since the question doesnt talk about prompting the user to enter again after an invalid entry message is thrown , the same has not been implemented. Also, that would also require the question to state as to how many tries is allowed before the user is exited from buying .

Modified Code:

package com.chegg.question6;

import java.awt.GridLayout;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import java.text.DecimalFormat;

import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JLabel;

import javax.swing.JOptionPane;

import javax.swing.SwingConstants;

public class CandyMachine

extends JFrame implements ActionListener

{

  

  

private static final long serialVersionUID = 1L;

//set constants for cost of items

//Note : values are not given in question

//These are assumed values .Can be change as per requirement

private static double CANDY_COST=50;

private static double CHIP_COST=40;

private static double GUM_COST=30;

private static double COOKIES_COST=20;

private JLabel headerTop=new JLabel("WELCOME TO SHELLY'S CANDY SHOP"

,SwingConstants.CENTER);

private JLabel headerBottom=new JLabel("To Make a Selection,Check the Product Price"

,SwingConstants.CENTER);

private JButton candyBtn;

private JButton chipsBtn;

private JButton gumBtn;

private JButton cookiesBtn;

private JButton exitBtn;

//constructor to intialize the frame

public CandyMachine()

{

setTitle("Candy Machine");

setSize(350, 350);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

setLocationRelativeTo(null);

setLayout(new GridLayout(7, 1));

add(headerTop);

add(headerBottom);

  

//create a button and add action lister for candy button

candyBtn=new JButton("Candy");

candyBtn.addActionListener(this);

add(candyBtn);

//create a button and add action lister for chips button

chipsBtn=new JButton("Chips");

chipsBtn.addActionListener(this);

add(chipsBtn);

//create a button and add action lister for genms button

gumBtn=new JButton("Gum");

gumBtn.addActionListener(this);

add(gumBtn);

//create a button and add action lister for chocolate button

cookiesBtn=new JButton("Cookies");

cookiesBtn.addActionListener(this);

add(cookiesBtn);

//create a button and add action lister for exit button

exitBtn=new JButton("Exit");

exitBtn.addActionListener(this);

add(exitBtn);

//set visibility true

setVisible(true);

}

public static void main(String[] args)

{

//instantiate the class

new CandyMachine();

}

/**Override the actionPerformed method that handles

* the five buttons*/

public void actionPerformed(ActionEvent ae) {

String item=ae.getActionCommand();

Object obj=(JButton)ae.getSource();

double cost=0;

double change=0;

DecimalFormat df=new DecimalFormat("##.00");

//check if button is candy

if(obj==candyBtn)

{

try {

do

{

cost=Double.parseDouble(JOptionPane.showInputDialog(null,

"To buy "+item+" please insert "+CANDY_COST+" cents",

"Input",

JOptionPane.QUESTION_MESSAGE));

  

if(cost<CANDY_COST)

JOptionPane.showMessageDialog(null, "Not sufficient Amount");

  

}while(cost<CANDY_COST);

}

catch (NumberFormatException ne){

JOptionPane.showMessageDialog(null, "Incorrect input. Insert "+ CANDY_COST+ " cents for candy");

}

if(cost !=0.0){ // This "If" clause is to ensure change message doesnt come up after an error because if an error occurs cost will be 0.0

change=cost-CANDY_COST;

if(change!=0)

JOptionPane.showMessageDialog(null,

"Change : "+df.format(change)+" Please pick up your "+item+" and enjoy",

"Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);

else

JOptionPane.showMessageDialog(null,

"Please pick up your "+item+" and enjoy",

"Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);

}

}

//check if button is chips

else if(obj==chipsBtn)

{

try {

do

{

cost=Double.parseDouble(JOptionPane.showInputDialog(null,

"To buy "+item+" please insert "+CHIP_COST+" cents",

"Input",

JOptionPane.QUESTION_MESSAGE));

if(cost<CHIP_COST)

JOptionPane.showMessageDialog(null, "Not sufficient Amount");

  

}while(cost<CHIP_COST);

}

catch (NumberFormatException ne){

JOptionPane.showMessageDialog(null, "Incorrect input. Insert "+ CHIP_COST+ " cents for CHIP");

}

if(cost !=0.0){ // This "If" clause is to ensure change message doesnt come up after an error because if an error occurs cost will be 0.0

  

change=cost-CHIP_COST;

if(change!=0)

JOptionPane.showMessageDialog(null,

"Change : "+df.format(change)+" Please pick up your "+item+" and enjoy",

"Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);

else

JOptionPane.showMessageDialog(null,

"Please pick up your "+item+" and enjoy",

"Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);

}

}

//check if button is gum

else if(obj==gumBtn)

{

try{

do

{

cost=Double.parseDouble(JOptionPane.showInputDialog(null,

"To buy "+item+" please insert "+GUM_COST+" cents",

"Input",

JOptionPane.QUESTION_MESSAGE));

if(cost<GUM_COST)

JOptionPane.showMessageDialog(null, "Not sufficient Amount");

  

}while(cost<GUM_COST);

}

catch (NumberFormatException ne)

{

JOptionPane.showMessageDialog(null, "Incorrect input. Insert "+ GUM_COST+ " cents for GUM");

}

if(cost !=0.0){ // This "If" clause is to ensure change message doesnt come up after an error because if an error occurs cost will be 0.0

  

change=cost-GUM_COST;

  

if(change!=0)

JOptionPane.showMessageDialog(null,

"Change : "+df.format(change)+" Please pick up your "+item+" and enjoy",

"Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);

else

JOptionPane.showMessageDialog(null,

"Please pick up your "+item+" and enjoy",

"Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);

}

}

//check if button is cookies

else if(obj==cookiesBtn)

{

try{

do

{

cost=Double.parseDouble(JOptionPane.showInputDialog(null,

"To buy "+item+" please insert "+COOKIES_COST+" cents",

"Input",

JOptionPane.QUESTION_MESSAGE));

if(cost<COOKIES_COST)

JOptionPane.showMessageDialog(null, "Not sufficient Amount");

  

}while(cost<COOKIES_COST);

}

catch (NumberFormatException ne)

{

JOptionPane.showMessageDialog(null, "Incorrect input. Insert "+ COOKIES_COST+ " cents for COOKIES");

}

if(cost !=0.0){ // This "If" clause is to ensure change message doesnt come up after an error because if an error occurs cost will be 0.0

  

change=cost-COOKIES_COST;

if(change!=0)

JOptionPane.showMessageDialog(null,

"Change : "+df.format(change)

+" Please pick up your "

+item+" and enjoy",

"Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);

else

JOptionPane.showMessageDialog(null,

"Please pick up your "+item+" and enjoy",

"Thank you.Come again!",JOptionPane.PLAIN_MESSAGE);

}

}

//check if button is exit

else if(obj==exitBtn)

{

JOptionPane.showMessageDialog(null, "Thank you.Come again!");

System.exit(0);

}

}

}

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