Java Examples - Find common elements from arrays

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