How to find common elements from arrays in Java

Problem Description

How to find common elements from arrays?

Solution

Following example shows how to find common elements from two arrays and store them in an array.

import java.util.ArrayList;

public class NewClass {
   public static void main(String[] args) {
      ArrayList objArray = new ArrayList();
      ArrayList objArray2 = new ArrayList();
      objArray2.add(0,"common1");
      objArray2.add(1,"common2");
      objArray2.add(2,"notcommon");
      objArray2.add(3,"notcommon1");
      objArray.add(0,"common1");
      objArray.add(1,"common2");
      objArray.add(2,"notcommon2");
      System.out.println("Array elements of array1"+objArray);
      System.out.println("Array elements of array2"+objArray2);
      objArray.retainAll(objArray2);
      System.out.println("Array1 after retaining common elements of array2 & array1"+objArray);
   }
}

Result

The above code sample will produce the following result.

Array elements of array1[common1, common2, notcommon2]
Array elements of array2[common1, common2, notcommon,
notcommon1]
Array1 after retaining common elements of array2 & array1
[common1, common2]

Another sample example of Find common elements from arrays

public class HelloWorld {
   public static void main(String a[]) {
      int[] arr1 = {4,7,3,9,2};
      int[] arr2 = {3,2,12,9,40,32,4};
      
      for(int i = 0;i < arr1.length; i++) {
         for(int j = 0; j < arr2.length; j++) {
            if(arr1[i] == arr2[j]) { 
               System.out.println(arr1[i]);
            } 
         } 
      }
   }
}

The above code sample will produce the following result.

4 
3 
9 
2