Hare is an example that compare two array lists and display the common elements from both of them.

import java.util.*;

public class DisplayCommonElement{
  public static void main(String[]args){
    ArrayList a1 = new ArrayList();
    ArrayList a2 = new ArrayList();
     a1.add("a");
     a1.add("b");
     a1.add("c");

    a2.add("a");
    a2.add("b");
    a2.add("c"); 
    a2.add("d");
    a2.add("e");
        int array1Size = a1.size();
        int array2Size = a2.size();
        if (a1.size() > a2.size()) {
            int k = 0;
            for (int i = 0; i < a2.size(); i++)            {
                if (((String)a1.get(i)).equals((String)a2.get(i)))  {
                    System.out.println((String)a2.get(i));
                }
                k = i;
            }
           }
        else {
           int k = 0;
            for (int i = 0; i < a1.size(); i++) {
                if (((String)a1.get(i)).equals((String)a2.get(i))) {
                    System.out.println((String)a1.get(i));
                }
                k = i;
            }
         }
  }
}