Array Reallocation : Array Basics « Collections « Java Tutorial

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2. Collections
3. Array Basics

You can make a clone of an array and make the new array have a different size.

public static boolean[] copyOf (boolean[] original, int newLength)

public static byte[] copyOf (byte[] original, int newLength)

public static char[] copyOf (char[] original, int newLength)

public static double[] copyOf (double[] original, int newLength)

public static float [] copyOf (float[] original, int newLength)

public static int[] copyOf (int[] original, int newLength)

public static long[] copyOf (long[] original, int newLength)

public static short[] copyOf (short[] original, int newLength)

public static <T> T[] copyOf (T[] original, int newLength)

public static <T,U> T[] copyOf (U[] original, int newLength,java.lang.Class<? extends T[]> newType)

The last method allows you to upcast each element in the original array to a parent type.

Another method similar to copyOf that is also added to Arrays in Java 6 is copyOfRange.

copyOfRange copies a range of elements to a new array.

Like copyOf, copyOfRange also provides overrides for each Java data type.

Here are their signatures:

public static boolean[] copyOfRange (boolean[] original,int from, int to)

public static byte[] copyOfRange (byte[] original,int from, int to)

public static char[] copyOfRange (char[] original,int from, int to)

public static double[] copyOfRange (double[] original,int from, int to)

public static float[] copyOfRange (float[] original,int from, int to)

public static int[] copyOfRange (int[] original, int from, int to)

public static long[] copyOfRange (long[] original, int from, int to)

public static short[] copyOfRange (short[] original, int from, int to)

public static <T> T[] copyOfRange (T[] original, int from, int to)

public static <T,U> T[] copyOfRange (U[] original, int from,int to, java.lang.Class<? extends T[]> newType)

Array reallocation example

import java.util.Arrays;

public class ArrayReallocationDemo {

  public static void main(String[] args) {
    int[] data1 = new int[] { 1, 3, 5, 7, 9 };

    printArray(data1);
    int[] data2 = Arrays.copyOf(data1, 6);
    data2[5] = 11;
    printArray(data2);

    int[] data3 = Arrays.copyOfRange(data1, 2, 10);
    printArray(data3);
  }

  // print array elements
  private static void printArray(int[] data) {
    StringBuilder stringBuilder = new StringBuilder("[");
    for (int i = 0; i < data.length; i++) {
      stringBuilder.append(data[i]);
      if (i < data.length - 1)
        stringBuilder.append(", ");
    }
    stringBuilder.append("]");
    System.out.println(stringBuilder);
  }
}

[1, 3, 5, 7, 9]
[1, 3, 5, 7, 9, 11]
[5, 7, 9, 0, 0, 0, 0, 0]