Question

Java debugging in eclipse

You are to debug the given file FindTheErrors.java. The code has four individual problems Problems 2- 4 have been commented out. Fix Problem 1 and get it running correctly before moving on to Problem 2. Continue this way until the whole program runs properly. The comments in the program will tell you what each problem should do. In your final submission, all of the four parts will be uncommented and work correctly. The existing code is as follows:

package edu.ilstu;
import java.util.Scanner;
/**
* The following class has four independent debugging
* problems. Solve one at a time, uncommenting the next
* one only after the previous problem is working correctly.
*/
public class FindTheErrors {
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
/*
* Problem 1 Debugging
*
* This problem is to read in your first name,
* last name, and current year and display them in
* a sentence to the console.
*/
String firstName = "";
String lastName = "";
String school = "";
int year = 0;
System.out.print("Enter your first name: ");
firstName = keyboard.nextLine();
System.out.print("Enter the current year: ");
year = keyboard.nextInt();
System.out.print("Enter your last name: ");
lastName = keyboard.nextLine();
System.out.println("You are " + firstName + " "
+ lastName + " and it is the year " + year);
keyboard.nextLine();
System.out.println("\n");
/*
* Problem 2 Debugging
*
* This problem is to assign a value to num2 based on
* the input value of num1. It should then print both
* numbers.
*/
// int num1 = 0;
// int num2 = 0;
//
// System.out.print("Enter a number - 1, 2, or 3: ");
// num1 = keyboard.nextInt();
//
// if (num1 == 1);
// num2 = 2;
// else if (num1 == 2);
// num2 = 3;
// else if (num1 == 3);
// num2 = 4;
//
// System.out.println("num1 = " + num1
// + " and num2 = " + num2);
//
// System.out.println("\n");
/*
* Problem 3
*
* This problem is to read the name of the course
* you are taking and display a statement showing the
* answer.
*/
// String courseName = "";
//
// System.out.print(
"Enter your course name (IT168 or IT177): ");
// courseName = keyboard.nextLine();
// if (courseName == IT168))
// System.out.println("You are taking IT168.");
// else if (courseName == IT177))
// System.out.println("You are taking IT177.");
// else
// System.out.println("Invalid input.");
//
// System.out.println("\n");
/*
* Problem 4
*
* This problem is to read a test grade from the
* keyboard and assign the appropriate letter grade.
*/
// int score = 0;
// char grade = 'Z';
//
// System.out.println("Enter your test grade (1-100): ");
// score = keyboard.nextInt();
//
// switch(score)
// {
// case (score > 60):
// grade = 'A';
// break;
// case (score > 70):
// grade = 'b';
// break;
// case (score > 80):
// grade = 'C';
// break;
// case (score > 90):
// grade = 'D';
// break;
// default:
// grade = 'F';
// }
//
// System.out.println("The score " + score
// + " will have a grade of " + grade + ".");
}
}

Answer 1

explainations are added in comments on lines which are altered.

fixed Java code -

package edu.ilstu;
import java.util.Scanner;
/**
* The following class has four independent debugging
* problems. Solve one at a time, uncommenting the next
* one only after the previous problem is working correctly.
*/
public class FindTheErrors {
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
/*
* Problem 1 Debugging
*
* This problem is to read in your first name,
* last name, and current year and display them in
* a sentence to the console.
*/
String firstName = "";
String lastName = "";
String school = "";
int year = 0;
System.out.print("Enter your first name: ");
firstName = keyboard.nextLine();
System.out.print("Enter the current year: ");
year = keyboard.nextInt();
System.out.print("Enter your last name: ");
lastName = keyboard.next(); /*nextLine parses input until it finds newline character('\n'),so the string left after reading by nextInt(),
so it is reading what's left of previous line,(that's why it is printing line without taking next input,
while next() parse the next valid string so it skips the previous input and scans the next string of valid characters*/
System.out.println("You are " + firstName + " "
+ lastName + " and it is the year " + year);
keyboard.nextLine();
System.out.println("\n");
/*
* Problem 2 Debugging
*
* This problem is to assign a value to num2 based on
* the input value of num1. It should then print both
* numbers.
*/
int num1 = 0;
int num2 = 0;

System.out.print("Enter a number - 1, 2, or 3: ");
num1 = keyboard.nextInt();

if (num1 == 1) //removed the ';' as it terminates the if condition here and would have any effect on further lines
num2 = 2;
else if (num1 == 2) //similarly removed ';'
num2 = 3;
else if (num1 == 3) //removed ';'
num2 = 4;

System.out.println("num1 = " + num1
+ " and num2 = " + num2);

System.out.println("\n");
/*
* Problem 3
*
* This problem is to read the name of the course
* you are taking and display a statement showing the
* answer.
*/
String courseName = "";

System.out.print("Enter your course name (IT168 or IT177): ");
courseName = keyboard.next(); //converted nextLine to next() because of reason previously stated in problem 1
if (courseName.equals("IT168")) // the '==' operator is not valid in case of strings, hence equals method is called to match strings
System.out.println("You are taking IT168.");
else if (courseName.equals("IT177")) //same case   
System.out.println("You are taking IT177.");
else
System.out.println("Invalid input.");

System.out.println("\n");
/*
* Problem 4
*
* This problem is to read a test grade from the
* keyboard and assign the appropriate letter grade.
*/
int score = 0;
char grade = 'Z';

System.out.println("Enter your test grade (1-100): ");
score = keyboard.nextInt();
// to convert the range of marks like(60-70) to single integers, we are dividing it by 10.
switch((int)score/10) //to convert the range to single digit
{
case 6: //cases from 60 to 69
grade = 'D';
break;
case 7: //cases from 70 to 79
grade = 'C';
break;
case 8: //cases from 80-89
grade = 'B';   
break;
case 9: //cases from 90-99
case 10: //case of 100
grade = 'A'; //this will be executed for both cases 9 and 10
break;
default:
grade = 'F'; //other cases (0-59)
}

System.out.println("The score " + score
+ " will have a grade of " + grade + ".");
}
}

output screenshot -

run: Enter your first name: adam Enter the current year: 2019 Enter your last name: apple You are adam apple and it is the year 2019 Enter a number - 1, 2, or 3: 2 numl- 2 and num2 3 Enter your course name (IT168 or IT177) IT177 You are taking IT177 Enter your test grade (1-100): 75 The score 75 will have a grade of C BUILD SUCCESSFUL (total time: 30 seconds)