Java Tutorial/Collections/Array Copy Clone

Array clone

public class MainClass {
  public static void main (String args[]) {
    int array1[] = {1, 2, 3, 4, 5};
    int[] clone = (int[]) array1.clone();    
    for(int i: clone){
      System.out.println(i);  
    }
    
  }
}

1
2
3
4
5

Copies the given array and adds the given element at the end of the new array. (long value type)

/*   Copyright 2004 The Apache Software Foundation
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *  limitations under the License.
 */

import java.lang.reflect.Array;

/**
 * <p>Operations on arrays, primitive arrays (like <code>int[]</code>) and
 * primitive wrapper arrays (like <code>Integer[]</code>).</p>
 * 
 * <p>This class tries to handle <code>null</code> input gracefully.
 * An exception will not be thrown for a <code>null</code>
 * array input. However, an Object array that contains a <code>null</code>
 * element may throw an exception. Each method documents its behaviour.</p>
 *
 * @author Stephen Colebourne
 * @author Moritz Petersen
 * @author 
 * @author Maarten Coene
 * @since 2.0
 * @version $Id: ArrayUtils.java 632503 2008-03-01 00:21:52Z ggregory $
 */
public class Main {
  
  /**
   * <p>Copies the given array and adds the given element at the end of the new array.</p>
   *
   * <p>The new array contains the same elements of the input
   * array plus the given element in the last position. The component type of 
   * the new array is the same as that of the input array.</p>
   *
   * <p>If the input array is <code>null</code>, a new one element array is returned
   *  whose component type is the same as the element.</p>
   * 
   * <pre>
   * ArrayUtils.add(null, 0)   = [0]
   * ArrayUtils.add([1], 0)    = [1, 0]
   * ArrayUtils.add([1, 0], 1) = [1, 0, 1]
   * </pre>
   * 
   * @param array  the array to copy and add the element to, may be <code>null</code>
   * @param element  the object to add at the last index of the new array
   * @return A new array containing the existing elements plus the new element
   * @since 2.1
   */
  public static long[] add(long[] array, long element) {
      long[] newArray = (long[])copyArrayGrow1(array, Long.TYPE);
      newArray[newArray.length - 1] = element;
      return newArray;
  }
  
  /**
   * Returns a copy of the given array of size 1 greater than the argument. 
   * The last value of the array is left to the default value.
   * 
   * @param array The array to copy, must not be <code>null</code>.
   * @param newArrayComponentType If <code>array</code> is <code>null</code>, create a 
   * size 1 array of this type.
   * @return A new copy of the array of size 1 greater than the input.
   */    
  private static Object copyArrayGrow1(Object array, Class newArrayComponentType) {
      if (array != null) {
          int arrayLength = Array.getLength(array);
          Object newArray = Array.newInstance(array.getClass().getComponentType(), arrayLength + 1);
          System.arraycopy(array, 0, newArray, 0, arrayLength);
          return newArray;
      }
      return Array.newInstance(newArrayComponentType, 1);
  }

}

Copying and Cloning Arrays

public class MainClass {
  public static void main (String args[]) {
    int array1[] = {1, 2, 3, 4, 5};
    int array2[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
    System.out.println("Original size: " + array1.length);
    System.out.println("New size: " + doubleArray(array1).length);
    System.out.println("Original size: " + array2.length);
    System.out.println("New size: " + doubleArray(array2).length);
  }
  static int[] doubleArray(int original[]) {
    int length = original.length;
    int newArray[] = new int[length*2];
    System.arraycopy(original, 0, newArray, 0, length);
    return newArray;
  }
}

Original size: 5
New size: 10
Original size: 9
New size: 18

Copy some items of an array into another array

public class Main {
  public static void main(String[] args) {
    String[] letters = { "A", "I", "U", "E", "O" };
    String[] results = new String[3];
    System.arraycopy(letters, 2, results, 0, 3);
    for (int i = 0; i < results.length; i++) {
      System.out.println("result = " + results[i]);
    }
  }
}

Doubling the size of an array

public class MainClass {
  public static void main (String args[]) {
    int array1[] = {1, 2, 3, 4, 5};
    int array2[] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
    System.out.println("Original size: " + array1.length);
    System.out.println("New size: " + doubleArray(array1).length);
    System.out.println("Original size: " + array2.length);
    System.out.println("New size: " + doubleArray(array2).length);
  }
  static int[] doubleArray(int original[]) {
    int length = original.length;
    int newArray[] = new int[length*2];
    System.arraycopy(original, 0, newArray, 0, length);
    return newArray;
  }
}

Original size: 5
New size: 10
Original size: 9
New size: 18

use Arrays.copyOf to copy array

import java.util.Arrays;
class MainClass
{
    public static void main(String args[])
    {
        int arrayOriginal[] = {42, 55, 21};
        int arrayNew[] =
            Arrays.copyOf(arrayOriginal, 3);             
        printIntArray(arrayNew);
    }
    static void printIntArray(int arrayNew[])
    {
        for (int i : arrayNew)
        {
            System.out.print(i);
            System.out.print(" ");
        }
        System.out.println();
    }
}

Using Arrays.copyOf to copy an array

import java.util.Arrays;
public class ArrayCopy {
  public static void main(String args[]) {
    System.out.printf("Before (original)\t%s%n", Arrays.toString(args));
    String copy[] = Arrays.copyOf(args, 4);
    System.out.printf("Before (copy)\t\t%s%n", Arrays.toString(copy));
    copy[0] = "A";
    copy[1] = "B";
    copy[2] = "C";
    copy[3] = "D";
    System.out.printf("After (original)\t%s%n", Arrays.toString(args));
    System.out.printf("After (copy)\t\t%s%n", Arrays.toString(copy));
  }
}