Printing an ArrayList of Objects as a table with non-fixed size in Java

I'm going to assume you have something like a Person object like this

public class Person
{
     public String fName;
     public String lName;
     public String age;
}

1. Implement your own list which will keep a track of the widths as you add elements to it, something like (very crude example)

   public class MyList<T extends Person> extends ArrayList<T>
   {
       public int[] colWidths = new int[3];
   
       @Override
       public boolean add(T e)
       {
            colWidths[0] = (colwidths[0] > e.fName.length()) ? colwidths[0] : e.fName.length();
            colWidths[1] = (colwidths[1] > e.lName.length()) ? colwidths[1] : e.lName.length();
            colWidths[2] = (colwidths[2] > e.age.length()) ? colwidths[2] : e.age.length();
   
            return super.add(e);
       }
   }
   

2. Iterate your list to calculate the max widths

   public int[] colWidths = new int[3];
   for(Person p : yourList)
   {
            colWidths[0] = (colwidths[0] > p.fName.length()) ? colwidths[0] : p.fName.length();
            colWidths[1] = (colwidths[1] > p.lName.length()) ? colwidths[1] : p.lName.length();
            colWidths[2] = (colwidths[2] > p.age.length()) ? colwidths[2] : p.age.length();
   }
   

   The obvious down side of this second approach is that you will need to iterate your list twice.

Then define a print method using these max widths (for example)

public void printMyList(List<Person> aList, int[] maxColWidths)
{
     // Do your printing
}

This question should help out with a method to format a string centered if required.

You would need the maximum length for each column beforehand. Then you can adapt your table header accordingly and start printing. Sadly I do not know of any other way to pretty-print this to the console.

I agree with Rudy Velthuis above. The code should iterate in order to get the biggest value of the String, then paint the box around the text. Should be like this:

import java.util.Scanner;

public class GettingBiggerName {

    static String firstName, secondName, thirdName; // testing with just 3 Strings that will be inserted in an Array

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        System.out.print("Enter first name: ");
        firstName = in.nextLine();

        System.out.print("Enter second name: ");
        secondName = in.nextLine();

        System.out.print("Enter third name: ");
        thirdName = in.nextLine();

        System.out.println();

        String[] arrayOne = { firstName, secondName, thirdName }; // Created the array with the 3 strings for testing purpose

        int count=0; int progress = 0;
        for (int i = 0; i < arrayOne.length; i++) { // iterating to get the biggest length of the Strings inside the array

            if (arrayOne[i].length() > arrayOne[progress].length()) {
                count = arrayOne[i].length();
                progress++;
            }

            else {
                count = arrayOne[progress].length();
            }

        }

        System.out.println("Printing the header of the box: ");

        // printing the box to fit the length of the biggest String inside the array
        for (int i = 0; i < count; i++) {
            System.out.print("=");

        }

    }

}