Question

How can the classes be modified to satisfy the comments & example tester:

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;

            }

        }

    }

}

When tested, for instance:

Enter a number (-1 to exit): 3857

x = 3857

Enter a number (-1 to exit): -4

x = -4

Enter a number (-1 to exit): 2m2

Could not read integer. InvalidIntegerException: Non-numerical character 'm' encountered.

Enter a number (-1 to exit): 13-4

Could not read integer. InvalidIntegerException: Non-numerical character '-' encountered.

Enter a number (-1 to exit): -ry24x

Could not read integer. InvalidIntegerException: Symbol '-' followed by non-numerical character 'r' encountered.

Enter a number (-1 to exit): 200

x = 200

Enter a number (-1 to exit): -1

x = -1

Goodbye!

Answer 1

Answer :

Code follows :

// ParserTester.java

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;
}
catch (InvalidIntegerException e) {
System.out.println("Could not read integer. " + e);
  
}
}
}
}

// Parser.java

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;
}

public int readInt () throws InvalidIntegerException, IOException {
//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.
int ch;
String s = "";
String badChar = "";
boolean firstch = true, firstminus = false;
  
while (true) {
ch = in.read ();
if (firstch) {
if ((Character.isDigit(ch)) || (ch == '-') ) {
if (ch == '-')
firstminus = true;
s += (char) ch;
firstch = false;
continue;
}
}
else {
if (Character.isDigit(ch)) {
s += (char) ch;
continue;
}
}
if ((ch == -1) || (Character.isWhitespace ((char) ch)) ) break;
if (badChar == "")
badChar += (char) ch;
}
if (badChar == "")
return (Integer.parseInt (s));
else if (firstminus)
throw (new InvalidIntegerException ("Symbol '-' followed by non numerical character '" + badChar + "' encountered."));
else
throw (new InvalidIntegerException ("Non numerical character '" + badChar + "' encountered."));
}
}

// Invalid integer exception
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);
  
}
}

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