int[] arr1={1, 2, 3, 4, 5, 6}; //first array
int[] arr2={7, 8, 9, 0}; //second array
int[] arr3={1, 2, 3, 4, 5, 6, 7, 8, 9, 0} //resultant array

There are following ways to merge two arrays:
1.Java arraycopy() method
2.Without using arraycopy() method
3.Java Collections
4.Java Stream API

1.Java arraycopy() method

Java arraycopy() is the method of System class which belongs to java.lang package.
It copies an array from the specified source array to the specified position of the destination array.
The number of elements copied is equal to the length argument.
Syntax:
public static void arraycopy(Object source, int source_position, Object destination, int destination_position, int length)
Parameters

• source: It is a source array.
• source_position: Starting point in the source array.
• destination: It is a destination array.
• destination_position: Starting position in the destination array.
• length: The number of array elements to be copied

NullPointerException
It throws NullPointerException if the source or destination array is null. It also throws ArrayIndexOutOfBoundsException if:

• source_position or destination_position or length is negative.
• source_position+length is greater than the length of the source array, or destination_position+length is - greater than the length of the destination array.

public class A{
    public static void main(String[] args) {
        int[] firstArray = {23,45,12,78,4,90,1};        //source array
        int[] secondArray = {77,11,45,88,32,56,3};  //destination array
        int fal = firstArray.length;        //determines length of firstArray
        int sal = secondArray.length;   //determines length of secondArray
        int[] result = new int[fal + sal];  //resultant array of size first array and second array
        System.arraycopy(firstArray, 0, result, 0, fal);
        System.arraycopy(secondArray, 0, result, fal, sal);
        System.out.println(Arrays.toString(result));    //prints the resultant array
    }
}

[23, 45, 12, 78, 4, 90, 1, 77, 11, 45, 88, 32, 56, 3]

according to the specified positions and length.

public class A{
    public static void main(String[] args) {
        int source_arr [] = { 11,22,33,44,55,98,76,54,60};
        int dest_arr[] = {66,77,88,99,22,67,21,90,80,70};
        int sourcePos = 2;
        int destPos = 4;
        int len = 3;
//invoking arraycopy() method
        System.arraycopy(source_arr, sourcePos, dest_arr,destPos, len);
// Print elements of destination after
        System.out.print("Resultant array : ");
        for (int i = 0; i < dest_arr.length; i++)
            System.out.print(dest_arr[i] + " ");
    }
}

Resultant array : 66 77 88 99 33 44 55 90 80 70 

2.Without using arraycopy() method

Manually copy the each element of both arrays to mergedArray and convert that array into String by using toString() method of Array class.

public class A{
    public static void main(String[] args) {
        int[] firstArray = {56,78,90,32,67,12}; //initialized array
        int[] secondArray = {11,14,9,5,2,23,15};
        int length = firstArray.length + secondArray.length; //add the length of firstArray into secondArray
        int[] mergedArray = new int[length];    //resultant array
        int pos = 0;
        for (int element : firstArray) //copying elements of secondArray using for-each loop
        {
            mergedArray[pos] = element;
            pos++;              //increases position by 1
        }
        for (int element : secondArray) //copying elements of firstArray using for-each loop
        {
            mergedArray[pos] = element;
            pos++;
        }
        System.out.println(Arrays.toString(mergedArray));   //prints the resultant array  
    }
}

[56, 78, 90, 32, 67, 12, 11, 14, 9, 5, 2, 23, 15]

3.Java Collections

Using the Arrays.asList() method.
Now we have created the list view of str2 and added all the elements of str2 into the list.
Again perform conversion from list to array and store the resultant array into str3 variable.

public class A{
    public static void main(String[] args) {
        String str1[] = { "A", "E", "I" };          //source array
        String str2[] = { "O", "U" };               //destination array
        List list = new ArrayList(Arrays.asList(str1)); //returns a list view of an array
//returns a list view of str2 and adds all elements of str2 into list
        list.addAll(Arrays.asList(str2));
        Object[] str3 = list.toArray();         //converting list to array
        System.out.println(Arrays.toString(str3));  //prints the resultant array
    }
}

[A, E, I, O, U]

4.Java Stream API

Stream.of() method
The Stream.of() method of Stream interface returns a sequential ordered stream whose elements are the values.

Syntax
static Stream of(T…values)
Explain：Where MT is the type of stream elements. The method accepts values (elements of the new stream).

flatMap() method
The flatMap() method is the method of Stream interface. It returns a stream consisting of the result.
Syntax
Stream flatMap(Function<? Super T, ? extends Stream<? Extends R>> mapper)
Explain：Where R is the element type of new stream. The method accepts a mapper (a function to apply to each element which produces a stream of new values) as a parameter.

toArray() method
The toArray() method of Stream interface returns an array containing the elements of the stream.
Syntax
Object[] toArray()文章來源地址http://www.zghlxwxcb.cn/news/detail-513345.html

public class A{
    // function to merge two arrays
    public static <T> Object[] mergeArray(T[] arr1, T[] arr2)
    {
        return Stream.of(arr1, arr2).flatMap(Stream::of).toArray();
    }
    public static void main (String[] args)
    {
        Integer[] firstArray = new Integer[]{13,12,11,6,9,3}; //source array
        Integer[] secondArray = new Integer[]{78,34,56,67,2,11,7}; //destination array
        Object[] mergedArray = mergeArray(firstArray,secondArray); //merged array
        System.out.println("Merged array: "+ Arrays.toString(mergedArray));
    }
}

Merged array: [13, 12, 11, 6, 9, 3, 78, 34, 56, 67, 2, 11, 7]

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