Question

How can the classes be modified to satisfy the comments:

public class InvalidIntegerException extends Exception{

    // Write a class for an InvalidIntegerException here

    //Constructor that takes no arguments

public InvalidIntegerException (){

super(); }

//Constructor that takes a string message

public InvalidIntegerException (String message){

super(message); }

}

import java.io.InputStream;
import java.io.IOException;

public class Parser {
    private InputStream in;

    public static final int CHAR_ZERO = (int) '0';

    public Parser (InputStream in) {
        this.in = in;
    }

    // Complete the following method as described in the assignment

    public int readInt () {

        //read characters from the InputStream in (an instance variable for the Parser class).

        // Specifically, your method should read the successive characters from in until the next whitespace character or end of stream is encountered the method Character.isWhitespace(char ch) will probably be helpful here

        // If those characters constitute an integer—i.e., are all digits 0 through 9, possibly starting with the - character—then readInt() should return the int whose decimal representation corresponds to these characters.

        //If a non-numerical character is encountered, readInt() should do the following:

        //Continue reading from in until the next whitespace character is read or the end of the stream is reached.

        //Throw an InvalidIntegerException with a message indicating the first non-numerical character encountered in in.

    }

}

import java.io.InputStream;

import java.io.IOException;

public class ParserTester {

    public static void main (String[] args) {

        Parser p = new Parser(System.in);

        int    x = 0;

        // Modify the loop below so that the code also catches

        // InvalidIntegerExceptions and prints the appropriate error message: Could not read integer followed by the details of the caught exception.

        // InvalidIntegerException should not break out of the main loop in the program—after an InvalidIntegerException, the user should be able to continue entering more values.

        //Note that an InvalidIntegerException should not break out of the main loop in the program—after an InvalidIntegerException, the user should be able to continue entering more values.

        while (true) {

            try {

                System.out.print("Enter a number (-1 to exit): ");

                x = p.readInt();

                System.out.println("x = " + x);

                if (x == -1) {

                    System.out.println("Goodbye!");

                    return;

                }

            }

            catch (IOException e) {

                System.out.println("Reading error: " + e);

                return;

            }

        }

    }

}

Answer 1

Here is the solution to above problem in Java. Please read the code comments for more information

JAVA CODE

import java.io.InputStream;
import java.io.IOException;
import java.util.*;

class Parser {
private InputStream in;

public static final int CHAR_ZERO = (int) '0';

public Parser()
{
  
}
public Parser(InputStream in) {
this.in = in;
}

// Complete the following method as described in the assignment

public int readInt () {

//read characters from the InputStream in (an instance variable for the Parser class).

// Specifically, your method should read the successive characters from in until the next whitespace character or end of stream is encountered the method Character.isWhitespace(char ch) will probably be helpful here

// If those characters constitute an integer—i.e., are all digits 0 through 9, possibly starting with the - character—then readInt() should return the int whose decimal representation corresponds to these characters.

//If a non-numerical character is encountered, readInt() should do the following:

//Continue reading from in until the next whitespace character is read or the end of the stream is reached.

//Throw an InvalidIntegerException with a message indicating the first non-numerical character encountered in in.
  
Scanner sc = new Scanner(System.in); //take input from User
char ch='_';
String integer="";
String input = sc.nextLine();
  
int index=0;
//repeat till space is not encountered
try {
while((ch!= ' ')&& index<input.length())
{
ch = input.charAt(index++);
//read the character
  
if(ch>='0'&&ch<='9') //if numeric value add to the string
integer+=ch;
else if(ch==' ') //if space encountered break
break;
else //if something else
throw new IOException("Invalid input " + ch);
}
//print the valid integer
return Integer.parseInt(integer);
  
} catch(IOException e) {
System.out.println(e.getMessage()); //print the failing character
return -1;
}
}
  

}

public class Main
{
public static void main(String [] args)
{
Parser p = new Parser();
int result=p.readInt();
if(result!=-1)
System.out.println("Integer is: " + result );
}
}

Screenshot of output