Challenging Java programs and succeeding in coding interviews-12

Welcome to part 12 “Java programs and succeeding in coding interviews”! In this tutorial, we will focus on finding and fixing logical errors in Java programs.

Logical errors are a common type of error that can be difficult to detect and fix. However, with practice and the right techniques, you can improve your logical thinking and become better at identifying and solving these errors.

By the end of this tutorial, you will have a better understanding of how to approach logical errors in Java programs, and your logical reasoning skills will have improved.

We hope that this tutorial will help you prepare for coding interviews and build your confidence as a Java developer. So let’s get started and dive into the world of logical error solving in Java programming!

Find and fix errors in the below Java program(1145)


public class JavaTechypid {
    public static void main(String[] args) {
        int x = 5;
        int y = 10;
        int z = sum(x, y);
        System.out.println("The sum of " + x + " and " + y + " is " + z);
    }

    public static int sum(int a, int b) {
        int result = a - b;
        return result;
    }
}

Find and fix errors in the below Java program(1156)

// This program is supposed to count the number of vowels in a given string

public class JavaTechypid {
    public static void main(String[] args) {
        String inputString = "Hello World!";
        int vowelCount = 0;
        for(int i = 0; i <= inputString.length(); i++) {
            char c = inputString.charAt(i);
            if(c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u') {
                vowelCount++;
            }
        }
        System.out.println("The number of vowels in the string is: " + vowelCount);
    }
}

Find and fix errors in the below Java program(1203)

public class JavaTechypid {
    public static void main(String[] args) {
        int n = 10;
        int sum = 0;
        for (int i = 0; i <= n; i++) {
            sum += i;
        }
        System.out.println("The sum of integers from 1 to " + n + " is: " + sum);
    }
}

Find and fix errors in the below Java program(1211)

public class JavaTechypid {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        int sum = 0;
        for (int i = 1; i <= numbers.length; i++) {
            sum += numbers[i];
        }
        System.out.println("The sum is: " + sum);
    }
}

Find and fix errors in the below Java program(1224)

public class JavaTechypid {
    public static void main(String[] args) {
        int[] arr = { 3, 5, 7, 9 };
        int n = arr.length;
        for (int i = 0; i <= n; i++) { 
            System.out.println(arr[i]);
        }
    }
}

Errors Solutions(1145)


public class JavaTechypid {
    public static void main(String[] args) {
        int x = 5;
        int y = 10;
        int z = sum(x, y);
        System.out.println("The sum of " + x + " and " + y + " is " + z);
    }

    public static int sum(int a, int b) {
        int result = a + b;
        return result;
    }
}

In the corrected program, the sum method has been corrected to actually calculate the sum of the two numbers.

Program was intended to calculate the sum of two numbers, but due to a logical error in the sum method, it actually calculates the difference between the two numbers.

Errors Solutions(1156)

public class JavaTechypid {
    public static void main(String[] args) {
        String inputString = "Hello World!";
        int vowelCount = 0;
        for(int i = 0; i < inputString.length(); i++) {
            char c = inputString.charAt(i);
            if(c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u') {
                vowelCount++;
            }
        }
        System.out.println("The number of vowels in the string is: " + vowelCount);
    }
}

we need to change the condition of the for loop to run only while i < inputString.length().

The logical error on that program was that the for loop was running for one extra iteration beyond the length of the input string. This causes an IndexOutOfBoundsException to be thrown when trying to access the character at the last index of the string.

Errors Solutions(1203)

public class JavaTechypid {
    public static void main(String[] args) {
        int n = 10;
        int sum = 0;
        for (int i = 1; i <= n; i++) {
            sum += i;
        }
        System.out.println("The sum of integers from 1 to " + n + " is: " + sum);
    }
}

The corrected program has the loop condition as i <= n and starts the loop from i = 1, which gives the correct sum of integers from 1 to n.

The error in the above program was that the loop condition should be i < n instead of i <= n. This is because the loop starts from 0 and includes the number n, which results in the sum being one more than the actual sum.

Errors Solutions(1211)

public class JavaTechypid {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        int sum = 0;
        for (int i = 0; i < numbers.length; i++) {
            sum += numbers[i];
        }
        System.out.println("The sum is: " + sum);
    }
}

To fix this error, we need to change the loop condition to i < numbers.length and use numbers[i-1] to access the elements of the array.

The first element of the array is at index 0, not index 1.

This means that we will get an ArrayIndexOutOfBoundsException when i reaches numbers.length.

Errors Solutions(1224)

public class JavaTechypid {
    public static void main(String[] args) {
        int[] arr = { 3, 5, 7, 9 };
        int n = arr.length;
        for (int i = 0; i < n; i++) { // corrected loop condition: i < n
            System.out.println(arr[i]);
        }
    }
}

Error in the for loop condition

The loop should run until i is less than n, not less than or equal to n.

To fix this error, we need to change the loop condition to i < n instead of <= n.

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