merge sort java

MergeSort.java

class MergeSort {
    public void sort(int[] arr) {

            if (null == arr || arr.length == 0) {
                return;
            }
            merge_sort(arr);

   }

   private void merge_sort(int[] arr) {
       if(arr.length == 1) {
           return;
       }
       
       int[] leftarr = new int[arr.length/2];
       System.arraycopy(arr,0,leftarr,0,leftarr.length);

       int[] rightarr = new int[arr.length - leftarr.length];
       System.arraycopy(arr,leftarr.length,rightarr,0,rightarr.length);

       // recursion
       // sort the left array
       merge_sort(leftarr);

       // sor the right array
       merge_sort(rightarr);

       // merge the two arrays together
       merge(leftarr,rightarr,arr);
   }

   private void merge(int[] left, int[] right, int[] arr) {
       int[] tmpArray = new int[arr.length];
       int leftpos = 0;
       int rightpos = 0;
       int tmppos = 0;

       while(leftpos < left.length && rightpos < right.length) {
           if(left[leftpos] < right[rightpos]) {
               tmpArray[tmppos]  = left[leftpos];
               leftpos++;
           } else {
               tmpArray[tmppos] = right[rightpos];
               rightpos++;
           }
           tmppos++;
       }

       // copy the rest of the left array
       while(leftpos < left.length) {
           tmpArray[tmppos] = left[leftpos];
           tmppos++;
           leftpos++;
       }

       // copy the rest of the right array
       while(rightpos < right.length) {
           tmpArray[tmppos] = right[rightpos];
           tmppos++;
           rightpos++;
       }

       for(int i=0; i < arr.length; i++) {
           arr[i] = tmpArray[i];
       }

   }

        

    public static void main(String[] args) {
        int[] intArr =  new int[] {1,60,10,2,7,90,100,35};
        System.out.println("Before ----------");
        for(int val: intArr) {
            System.out.println(val);
        }
        MergeSort msort = new MergeSort();
        msort.sort(intArr);
        System.out.println("After ----------");
        for(int val : intArr) {
            System.out.println(val);
        }
    }
}