System Class arraycopy() Method In Java

Exploring java.lang > System >
Siva Nookala - 20 Feb 2017

The java.lang.System.arraycopy() method copies elements from the specified source array, beginning at the specified position, to the specified position of the destination array:

public static void arraycopy(Object source, int sourcePosition, Object destination, int destinationPosition, int numberOfElements)

source : Array from which elements are to be copied.
sourcePosition : Index that specifies the starting point in the range of elements to copy from the array. This value can be any valid array index.
destination : Specifies the destination array that will store the copy.
destinationPosition : Specifies the index in the destination array where the first copied element should be stored.
numberOfElements : Specifies the number of elements to copy from the array in the first argument.

NOTE:
The elements at positions sourcePosition to (sourcePosition + numberOfElements- 1)are copied into positions destinationPosition to (destinationPosition + numberOfElements – 1), respectively, of the destination array.

Exceptions thrown by arraycopy():

Exception	Description
`IndexOutOfBoundsException`	If copying causes access of data outside the range of array
`ArrayStoreException`	If it is not possible to store an element of the source array in the destination array because of a type mismatch
`NullPointerException`	If either source or destination is null

The following example shows the usage of arraycopy() method:

ArrayCopyDemo1

CODE

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class ArrayCopyDemo1
{
    public static void main(String arg[])
    {
        char array[] = {'J', 'a', 'v', 'a', 'i', 's', 'f', 'u', 'n'};
        char arrayCopy[] = new char[4];
        System.arraycopy(array, 0, arrayCopy, 0, 4);
        // Print characters as a string
        System.out.println(new String(arrayCopy));    
    }
}

OUTPUT

Java

DESCRIPTION

THINGS TO TRY

In the above program, change the last argument of arraycopy() from 4 to 3 or 2 and observe the change in the output.

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We can pull different ranges out of the source array by changing the second argument.

For Example :

System.arraycopy(charArray, 4, charArrayCopy, 0, 4) copies characters at positions 4 through 7 from the array to the destination array, arrayCopy. Remember that the indices we pass to the arraycopy() must be valid. Otherwise, an Exception will be thrown.

ArrayCopyDemo2

CODE

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class ArrayCopyDemo2
{
    public static void main(String arg[])
    {
        int array[] = {5, 1, 4, 9, 6, 2};
        int arrayCopy[] = new int[4];
        System.arraycopy(array, 0, arrayCopy, 0, arrayCopy.length);  // LINE A
        for (int e : arrayCopy)
            System.out.print(e + " ");    
    }
}

OUTPUT

5 1 4 9

DESCRIPTION

THINGS TO TRY

Make a change to the second argument of arraycopy() such that the destination array, arrayCopy here, will have elements {1, 4, 9, 6}.

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