Arrays.copyOfRange in Java with Example

Arrays.copyOfRange in Java with Example | The copyOfRange() method in java.util.Arrays class is given to copy the specified range of the specified array into a new array. There are many overloaded forms of Arrays.copyOfRange() method. All those forms were introduced in the Java1.6 version. The overloaded forms of Arrays.copyOfRange() method are,

  • public static byte[] copyOfRange(byte[] original, int from, int to)
  • public static short[] copyOfRange(short[] 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 char[] copyOfRange(char[] original, int from, int to)
  • public static float[] copyOfRange(float[] original, int from, int to)
  • public static double[] copyOfRange(double[] original, int from, int to)
  • public static boolean[] copyOfRange(boolean[] 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, Class<? extends T[]> newType)

In these methods the arguments are,

  • original:- The array from which a range is to be copied.
  • from:- The initial index of the range to be copied, it is inclusive.
  • to:- the final index of the range to be copied, exclusive. This index may lie outside the array.

The copyOfRange() method returns a new array containing the specified range from the original array, truncated or padded with zeros to obtain the required length.

Important points about these arguments:-

  • The length of the returned array will be tofrom.
  • The from must lie between zero and original.length (inclusive).
  • The value at original[from] is placed into the initial element of the copy (unless from == original.length or from == to).
  • Values from subsequent elements in the original array are placed into subsequent elements in the copy.
  • The argument to, must be greater than or equal to the argument from, or may be greater than original.length, in that case default value is placed in all elements of the copy whose index is greater than or equal to original.length – from.

Arrays.copyOfRange() Example in Java

Let us demonstrate Arrays.copyOfRange() method with some examples.

import java.util.Arrays;

public class ArrayTest {
  public static void main(String[] args) {
    
    // original array
    int[] arr = {10, 20, 30, 40, 50};
    System.out.println("Original array = " +
                        Arrays.toString(arr));
    
    // Example1:- to copy first 3 elements to new array
    int[] newArray1 = Arrays.copyOfRange(arr, 0, 3);
    System.out.println("NewArray1 = " + 
                        Arrays.toString(newArray1));
    
    // Example2:- to copy 30 and 40 to new array 
    int[] newArray2 = Arrays.copyOfRange(arr, 2, 4);
    System.out.println("NewArray2 = " + 
                        Arrays.toString(newArray2));
    
    // Example3:- to copy only one element 40
    int[] newArray3 = Arrays.copyOfRange(arr, 3, 4);
    System.out.println("NewArray3 = " + 
                        Arrays.toString(newArray3));
    
    // Example4:- to copy complete array
    int[] newArray4 = Arrays.copyOfRange(arr, 0, arr.length);
    System.out.println("NewArray4 = " + 
                        Arrays.toString(newArray4));
    
    // Example5:- to copy last element of array
    int[] newArray5=Arrays.copyOfRange(arr, arr.length-1, arr.length);
    System.out.println("NewArray5 = " + 
                        Arrays.toString(newArray5));
    
    // Example6:- argument "to" can be greater than arr.length
    int[] newArray6 = Arrays.copyOfRange(arr, 0, 10);
    System.out.println("NewArray6 = " + 
                        Arrays.toString(newArray6));

  }
}

Output:-

Original array = [10, 20, 30, 40, 50]
NewArray1 = [10, 20, 30]
NewArray2 = [30, 40]
NewArray3 = [40]
NewArray4 = [10, 20, 30, 40, 50]
NewArray5 = [50]
NewArray6 = [10, 20, 30, 40, 50, 0, 0, 0, 0, 0]

How it is implemented?

The Arrays.copyOfRange() method implementation is very similar to Arrays.copyof(). Similar to Arrays.copyof() method, internally this method is also calling System.arrayCopy() method which is a native method that uses System resources to copy the array to give high performance.

PrepBytes
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Whenever we call Arrays.copyOfRange() method then,
a) First of all it calculates the number of elements that should be copied from the original array. Length = to – from.
b) If the calculated length is less than 0 then it gives IllegalArgumentException.
c) One local array variable is created with the size of the calculated length.
d) Then it internally calls System.arraycopy() method.
e) Return the copied array.

Source code of copyOfRange() method to copy int array,

public static int[] copyOfRange(int[] original, int from, int to) {
    int newLength = to - from;
    if (newLength < 0)
        throw new IllegalArgumentException(from + " > " + to);
    int[] copy = new int[newLength];
    System.arraycopy(original, from, copy, 0,
                    Math.min(original.length - from, newLength));
    return copy;
}

Remaining overloaded forms of copyOfRange() method is implemented in similar way, return types are changing based on the passed argument type.

Exceptions thrown by Arrays.copyOfRange()

The exceptions thrown by Arrays.copyOfRange() method are,

  • ArrayIndexOutOfBoundsException if from < 0 or from > original.length
  • IllegalArgumentException if from > to
  • NullPointerException if original is null

Copy Multidimensional Array using copyOfRange() of Java Arrays

The Arrays.copyof() method also can be used to copy the Java multidimensional array like 2D Java array and 3D Java array.

Java program to find the copy of two dimensional (2D) Java array using Arrays.copyof() method,

import java.util.Arrays;

public class Matrix1 {
  public static void main(String[] args) {
    
    // original 2D array 3x2 
    int matrix[][] = { { 1, 2 }, { 4, 5 }, { 7, 8 } };
    System.out.println("Original = " + 
               Arrays.deepToString(matrix));

    // Example1:- Copy 1st and 2nd 1D array
    int[][] newMatrix1 = Arrays.copyOfRange(matrix, 0, 2);
    System.out.println("newMatrix1 = " + 
               Arrays.deepToString(newMatrix1));
    
    // Example2:- copy complete matrix
    int[][] newMatrix2 = Arrays.copyOfRange(matrix, 0, matrix.length);
    System.out.println("newMatrix2 = " + 
               Arrays.deepToString(newMatrix2));
    
    // Example3
    int[][] newMatrix3 = Arrays.copyOfRange(matrix, 2, 6);
    System.out.println("newMatrix3 = " + 
               Arrays.deepToString(newMatrix3));

  }
}

Output:-

Original = [[1, 2], [4, 5], [7, 8]]
newMatrix1 = [[1, 2], [4, 5]]
newMatrix2 = [[1, 2], [4, 5], [7, 8]]
newMatrix3 = [[7, 8], null, null, null]

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