java实现归并排序算法

public class MergeSort{
public static void main(String args[]){
int []a = {1,8,9,7,5,4,5,1,2,4,5,78,2};
mergeSort(a);

for(int i:a){
System.out.print(i+",");
}
}
public mergeSort(int[]a){
sort(a,0,a.length-1);
}
public static void sort(int []a,int L ,int R){
if(L<R){
int M = (L+R)/2;
sort(a,L,M);
sort(a,M+1,R);
merge(a,L,M,R);
}
}
public static void merge(int[]a,int L,int M,int R){
if(L<R){
int start1=L;
int end1=M;
int start2=M+1;
int end2=R;

int [] temp = new int [R-L+1];
int index = 0;

int i=start1;
int j=start2;
while(i<=end1&&j<=end2){
if(a[i]>=a[j]){
temp[index++]=a[i++];
}
else{
temp[index++]=a[j++];
}
}

while(i<=end1){
temp[index++]=a[i++];
}
while(j<=end2){
temp[index++]=a[j++];
}

for(index=0;index<temp.length;index++){
a[L+index]=temp[index];
}
}
}
}