ArrayList Copy Cloning Java

Note:

Before going through this program ArrayList copy Cloning, it is advised to read first ArrayList Introduction where all the methods, class signature, constructors and history are given.

4 programs are given on Arraylist.

1. ArrayList Methods: In this program, the basic operations on array list are performed like addition, checking the list is empty or not, removing the elements, knowing the index number of an element etc.
2. ArrayList Iterators: In this example, different styles of retrieving and printing the array list elements are described.
3. ArrayList Operations: In this program, operations like reversing, sorting, searching, swapping, shuffling, filling, knowing maximum and minimum values are performed. Finally, an array of array lists is created and the elements are printed.
4. ArrayList Special: In this program, operations like converting array list to array, array list to string, copying elements of one array into another, converting array to array list and finally cloning of an array list are performed.

This is the last program of the above four – ArrayList Special.

Example on ArrayList copy Cloning

import java.util.*;
public class ArrayListSpecial
{
  public static void main(String args[])
  {
    ArrayList al1 = new ArrayList();
    al1.add(10);
    al1.add(20);
    al1.add(30);
    System.out.println("\nElements of al1: " + al1);
                                           
                                              // CONVERTING TO ARRAY
    Object numbers[] = al1.toArray();
    System.out.print("Elements of al1 as array: ");
    for(Object obj : numbers)
    {
      System.out.print(obj + " ");
    }
                                              // CONVERTING TO STRING
    String str = al1.toString();
    System.out.println("\nElements of al1 as string: " + al1);
                                              // COPYING ELEMENTS
    ArrayList al2 = new ArrayList();    
    al2.add(100); 
    al2.add(200); 
    al2.add(300);
    al2.add(400);
    System.out.println("Elements of al2 before copying al1: " + al2);
    Collections.copy(al2, al1);
    System.out.println("Elements of al2 after copying al1: " + al2);

                                              // CLONING 	
    ArrayList al3 = (ArrayList) al1.clone();
    System.out.println("Cloned al3 elements: " + al3);

                                              // CONVERTING ARRAY TO ARRAYLIST
    Integer num[] = { new Integer(1), new Integer(2), new Integer(3) };
    List al4 = Arrays.asList(num);
    ArrayList al5 = new ArrayList(al4);
    System.out.println("al5 elements: " + al5);
  }
}

Output screenshot of ArrayList copy Cloning

       ArrayList al1 = new ArrayList();
       al1.add(10);

A generics ArrayList object al1 is created that accepts only integer values. With add() method three elements are added.

    
       Object numbers[] = al1.toArray();
       for(Object obj : numbers)
       {
         System.out.print(obj + " ");
       }

All the elements of al1 are converted into an array object numbers with toArray() method, inherited from Collection interface (and overridden by List interface). Using enhanced for loop all the elements are printed. Remember, toArray() method returns an object array of Object.

       String str = al1.toString();

Java allows many operations on data structures. A data structure class can be converted into a string so that a data structure can be used in string form, as required to place in a text field. The method used is toString() inherited from Object class.

       Collections.copy(al2, al1);

Another generic object al2 is created and copied all the elements of al1 into it with the static method copy() of Collections class. It is like addAll() method of Collection interface (overridden by List interface).

       ArrayList al3 = (ArrayList) al1.clone();

Any data structure can be cloned with clone() method of Object class. Cloning is more elaborately discussed in Cloning – Duplicating an Object – Marker Interface.

       Integer num[] = { new Integer(1), new Integer(2), new Integer(3) };
       List al4 = Arrays.asList(num);
       ArrayList al5 = new ArrayList(al4);

An Integer array object num is created with three Integer elements. The array num is converted into List by passing it to asList() method. Like this an array can be converted to a collections class, and also as did earlier, collections class can be converted to array using toArray() method. Finally, List is converted into ArrayList by passing List object al4 to ArrayList constructor.