java归并排序

public class MergeSort {
   public void mergeSort(int[] a,int left,int right){
      if(left<right){
         int middle = (left+right)/2;
         mergeSort(a, left, middle);
         mergeSort(a,middle+1,right);
         merge(a,left,middle,right);//合并
      }
   }

   private void merge(int[] a, int left, int middle, int right) {
      int [] tmpArray = new int[a.length];
      int rightStart = middle+1;
      int tmp = left;
      int third = left;
      //比较两个小数组相应下标位置的数组大小，小的先放进新数组
      while(left<=middle&&rightStart<=right){
         if(a[left]<=a[rightStart]){
            tmpArray[third++] = a [left++];
         }else{
            tmpArray[third++] = a[rightStart++];
         }
      }
      //如果左边还有数据需要拷贝，把左边数组剩下的拷贝到新数组
      while(left<=middle){
         tmpArray[third++] = a[left++];
      }
      //如果右边还有数据......
      while(rightStart<=right){
         tmpArray[third++] = a[rightStart++];
      }
      while(tmp<=right){
         a[tmp] = tmpArray[tmp++];
      }
   }

   public static void main(String[] args){
      MergeSort mergeSort = new MergeSort();
      int [] a = new int[]{90,3,2};
      mergeSort.mergeSort(a, 0, a.length-1);
      for(int n:a){
         System.out.print(" "+n);
      }
   }
}