Incorrect Loop in Java Program [closed]

Question 1

When retrieving an int with Scanner, remember to do a nextLine() to advance to the next line. Your case statements will run into each other because you do not have a break statement. And generally speaking, think about how the loop executes your statements and simplify things. For example (I only implemented add):

import java.util.Scanner;
import java.util.Random;

public class MathTutor {
    private static Random obj = new Random();

    public static int[] randomNumbers(){
        int arr[] = new int[2];   //init array to hold 2 numbers

        int x = obj.nextInt(99);
        int y = obj.nextInt(99);

        arr[0] = Math.max(x,y);
        arr[1] = Math.min(x, y);

        return arr;
    }

    public static void menu(){
        System.out.println("1. Addition Problem");
        System.out.println("2. Subtraction Problem");
        System.out.println("3. Multiplication Problem");
        System.out.println("4. Division Problem");
        System.out.println("5. Exit Program");
        System.out.print("Welcome! Please make a selection: ");
    }

    public static void main(String[] args) {

        int choice, answer;
        int[] number;
        Scanner input = new Scanner(System.in);

        do {
            menu();

            //get user's choice
            choice = input.nextInt();
            input.nextLine(); //ignore the rest of the line

            switch (choice)
            {
            case 1:
                number = randomNumbers();
                do {
                    System.out.print("What's " +number[0]+ " plus " +number[1]+ "?\n");
                    answer = input.nextInt();
                    input.nextLine();
                    if (answer != (number[0]+number[1]))
                        System.out.println("No! Please try again.");
                } while (answer != (number[0]+number[1]));

                System.out.println("\nCorrect!");           
                break;
            case 2:
                break;
            case 3:
                break;
            case 4:
                break;
            case 5:
                break;
            default:
                System.err.println("*** invalid selection ***");
                break;
            }
        } while (choice != 5);
        input.close();
        System.out.println("bye.");
    }
}

Question 2

Case statements in a switch will continue on unless you put a break/return/etc. statement to tell the program to go elsewhere.

For example:

switch(number) {
    case 0: {
        // do stuff
    }
    case 1: {
        // If number was 0 this case would still be entered!
        // The program "fell through" the end of case 0 and got here
    }
    ...
}

This is called switch fallthrough. Seems like an annoyance at times, but it does have its uses:

switch(number) {
    case 0:
    case 1:
    case 2: {
        // Do something if number is 0, 1, or 2
    }
    ...
}

To avoid fallthrough, add a break statement at the end of the case. This will cause the program to jump to the end of the switch statement:

switch(number) {
    case 0: {
        // do stuff
        break; // <-- Now if number is 0 case 1 won't be entered!
    }
    case 1: {
        // Only entered if number == 1 now
    }
    ...
}

You can also put return statements to exit a method entirely from a switch statement.

Also, minor quibble: Please use a more descriptive name than obj for your Random object. Also, the general convention for declaring arrays is to put the square brackets with the type, not with the name:

int[] arr; // conventional way of declaring arrays in Java
int arr[]; // works, but doesn't follow convention. Usually not a big deal, but still...

Also, when validating that the user's input was one of the options, you should use a do-while loop. The way you have it now, if I input an invalid value twice your code would still move on. And you have the menu() method; why not use that instead of all the System.out.println() calls?