Retrieve value from int array inside objects ArrayList

Question

i am experementing on ArrayList which contains different data types and an int array and I want to access a value from the array for example number 55. Can I directly access this array without using for-loops? How to override the toString method of this int array, so that I dont get entries like this: [I@2401f4c3? Also I dont know how to define for loop correcly because it prints the array just 1 time in console but it should print 4 times. Have any ideas please share with us.

ArrayTest class:

public class ArrayTest {

    public static void main(String[] args) {
        ArrayList<Object> strangeList = new ArrayList<>();

        strangeList.add("String");
        strangeList.add(3823);
        strangeList.add(new int[] { 329, 23882, 55, 932 });

        System.out.println(strangeList.size());
        System.out.println();

        for (int i = 0; i < strangeList.size(); i++) {
            if (i == 2) {
                for (int j = 0; j < strangeList.size(); j++) {
                    System.out.println(strangeList.get(j));
                }
            }
        }
    }
}

Arvind Kumar Avinash · Accepted Answer · 2021-03-26 23:21:59Z

Using obj.getClass().isArray(), check the type of obj if it is an array and if yes, print Arrays.toString((int[]) obj); otherwise, print obj where obj is an element from strangeList.

Demo:

import java.util.ArrayList;
import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        ArrayList<Object> strangeList = new ArrayList<>();

        strangeList.add("String");
        strangeList.add(3823);
        strangeList.add(new int[] { 329, 23882, 55, 932 });

        System.out.println(strangeList.size());
        System.out.println();

        for (int i = 0; i < strangeList.size(); i++) {
            Object obj = strangeList.get(i);
            Class<?> claz = obj.getClass();
            if (claz.isArray()) {
                if (claz.getComponentType() == int.class) {
                    System.out.println(Arrays.toString((int[]) obj));
                } else if (claz.getComponentType() == double.class) {
                    System.out.println(Arrays.toString((double[]) obj));
                }
                // ...
            } else {
                System.out.println(obj);
            }
        }
    }
}

Output:

3

String
3823
[329, 23882, 55, 932]

Teh · Accepted Answer · 2021-03-26 22:54:24Z

1

The second for loop you have goes over the same array not your int array to go through your int array you need to get that first. But since the starting array is of type object you need to "tell" (cast) java that it's actually an int array.

for (int i = 0; i < strangeList.size(); i++) {
    if (i == 2) {

        int[] myIntArray = (int[]) strangeList.get(2);
        for (int j = 0; j < myIntArray.length; j++) {
            System.out.println(myIntArray[j]);
        }
    }
}

edited Mar 26, 2021 at 22:54

answered Mar 26, 2021 at 22:40

Teh

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3 Comments

E.Y.309 Over a year ago

Hello Teh, thank you for your comment. I already try this out but The method size() is undefined for the type Object. It is not possible :/

E.Y.309 Over a year ago

Hey this one works fine thank you! I am thinking of making it more dynamically like what if it was an double[] instead of int[]. How we can check which type of array we have?

Teh Over a year ago

With something like this

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