java插入排序问题（字符串，一位数，二位数均能排序，但一位数与二位数混合排序不了，求解决）

[hqitboy]

import java.util.Scanner;

public class insertionSort {
public static void sort(Comparable<String>[] a){//将a[]按升序排列
int N = a.length;
for(int i = 1;i < N;i++){//将a[i]插入到a[i-1]、a[i-2]、a[i-3]···之中
for(int j = i;j > 0 && less(a[j],a[j-1]);j--)
exch(a,j,j-1);
}
}

private static boolean less(Comparable<String> v,Comparable<String> w){//比较两者大小，前者小于后者返回ture
return v.compareTo((String) w) < 0;
}

private static void exch(Comparable<String>[] a,int i,int j){// 交换两个数组
Comparable<String> t = a[i];
a[i] = a[j];
a[j] = t;
}

private static void show(Comparable<String>[] a){//在单行中打印数组
for(int i = 0;i<a.length;i++)
System.out.print(a[i] + ",");
System.out.println();
}

public static boolean isSorted(Comparable<String>[] a){//测试数组元素是否有序
for(int i = 1;i < a.length;i++)
if(less(a[i],a[i-1])) return false;
return true;
}

public static void main(String[] args) {

Scanner s = new Scanner(System.in);
System.out.println("请输入要排序的一组数并用逗号隔开：");
String inputString = s.next().toString();
String stringArray[] = inputString.split(",");
@SuppressWarnings("unchecked")
Comparable<String> a[] = new Comparable[stringArray.length];
for(int i = 0;i < stringArray.length;i++){
a[i] =(String)stringArray[i];
}
sort(a);
assert isSorted(a);
System.out.println("排序的结果为：");
show(a);
s.close();
}
}