Question

I have a text file containing the following content:

0 12
1 15
2 6
3 4
4 3
5 6
6 12
7 8
8 8
9 9
10 13

I want to read these integers from a txt file and save the two columns into two different arrays in Java.

Thanks to aioobe for his nice answer for the first part.

Now I want to develop it in this way:

1. Write a method called occurrence, that take a number as an input and write the number of occurrence that this number has.

2. Write another method called occurrences, that didn’t have any input, but as output it gives the number that has the major number of occurrences (in the second column) in the file.

3. At last, the Main program will ask the user to write a number from 1 to 3.

1= method that, from an input number (that is the number in the first column) gives back the associated number in the second column.

2= the first occurrence method (the one with input)

3= the second occurrence method (the one without input)

I wrote the code but there is some errors(about passing the array list to a method) and I need your help about that.
I am a JAVA novice, So if you feel that the code is not appropriate, please make the required changes.
This is my final code:

import java.util.*; //importing some java classes
import java.lang.*;
import java.io.*;

public class list {

    public static void main(String[] args) {

        // Read the text file and store them into two arrays:
        try {
            List<Integer> column1 = new ArrayList<Integer>();   // Defining an integer Array List
            List<Integer> column2 = new ArrayList<Integer>();   // Defining an integer Array List

            Scanner myfile = new Scanner(new FileReader("c:/java/data.txt")); // Reading file using Scanner

            while (myfile.hasNext()) {          // Read file content using a while loop
                column1.add(myfile.nextInt());      // Store the first integer into the first array list
                column2.add(myfile.nextInt());      // Store the next integer into the second array list
            }

            myfile.close(); // close the file

            System.out.println("column 1 elements are:\n" + column1);  // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
            System.out.println("column 2 elements are:\n" + column2);  // [12, 15, 6, 4, 3, 6, 12, 8, 8, 9, 13]

            //Getting a number(1-3) from user:
            Scanner cases = new Scanner(System.in);
            System.out.println("Enter a number between 1-3: "); 
            int num = cases.nextInt();

            switch (num) {
                case 1:
                    Scanner case1 = new Scanner(System.in);
                    System.out.println("Enter a number from first column to see how many occurrences it has: "); 
                    int numb = case1.nextInt();
                    System.out.println(column2.get(numb));
                    break;
                case 2:
                    occurrence(column2.toArray());
                    break;
                case 3:
                    occurrences(column2.toArray());
                    break;              
                default: System.out.println("the number is not 1 or 2 or 3!"); 
            }

        } catch (Exception e) {     // we defined it just in the case of error
            e.printStackTrace();    // shows the error
        }

    } // End of MAIN


    public void occurrence(int[] arg) { // Defining occurrence method

        int count = 0;

        //Getting a number from user input:
        Scanner userin = new Scanner(System.in);
        System.out.println("Enter an integer number: "); 
        int number = userin.nextInt();        

        // Finding the occurrences:
        for (int i = 0; i < arg.length; i++)
            if (arg[i] == number) count++;

        System.out.println( number + " is repeated " + count + " times in the second column.");
    } // End of occurrence method


    public void occurrences(int[] arg) {    // Defining occurrenceS method

        int max = 0;

        // Finding the maximum occurrences:
        for (int i = 1; i < arg.length; i++)
            if (arg[i] > arg[max]) max = i;
            System.out.println( max + " is the most repeated  number." );
    } // End of occurrenceS method


}

Answer 1

you are passing an Object[] while your method expects an int[]

(note that toArray() returns an Object[])

also, occurrence() is an instance method, while main is static, you will need to change occurrence() to be a static method as well, or create an instance of list.

so methods signature will be:

public static void occurrences(Integer[] arg) 

public static void occurrence(Integer[] arg)

and methods calls will be:

Integer[] temp = new Integer[column2.size()];
            switch (num) {
                case 1:
                    Scanner case1 = new Scanner(System.in);
                    System.out.println("Enter a number from first column to see how many occurrences it has: "); 
                    int numb = case1.nextInt();
                    System.out.println(column2.get(numb));
                    break;
                case 2:
                    occurrence(column2.toArray(temp));
                    break;
                case 3:
                    occurrences(column2.toArray(temp));
                    break;              
                default: System.out.println("the number is not 1 or 2 or 3!"); 
            }

p.s. this is not related to your question, but there is a strong java convention that a class name starts with a capital letter.