StringBuffer .insert方法输出电话号码格式

package ch11;

import java.util.Scanner;

/**
 * Created by liwenj on 2017/7/21.
 */
public class T7 {
    public static void main(String[] args) {
        String sz="13438377536";
        StringBuffer sb=new StringBuffer(sz);
        int len=sb.length();
        int index=len-4;
        while(true){
            if (index>0){
               sb.insert(index,"-");
                index=index-4;
            }else{
                break;
            }
        }
        System.out.println(sb);
    }
}