java代码 判断一个IP地址是否合法，并判断该地址是否属于一个给定的子网。

package com; import java.util.regex.Matcher; import java.util.regex.Pattern; public class CheckMask { public String isMask(){ int bt=255; int t=1; int x=0; String st=""; java.util.Scanner in = new java.util.Scanner(System.in); while(true){ System.out.print("请输入子网掩码1的个数:"); int a = in.nextInt(); if(a/8==0){ System.out.println("第一位必须是255,请重新输入！"); }else{ if(a%8==0){ for(int i= 0;i<a/8;i++){ st = st +String.valueOf(bt)+"."; } }else{ for(int i= 0;i<a/8;i++){ st = st +String.valueOf(bt)+"."; } for(int i=1;i<=a%8;i++){ for(int j=8-i;j>0;j--){ t = t*2; } x = x + t; t = 1; } bt = x; st = st +String.valueOf(bt)+"."; } if(st.length()/4<=4){ int length = 4 - st.length()/4; for(int i=0;i<length;i++){ st = st+"0"+"."; } } System.out.println("删之前"+st); st=st.substring(0, st.length() - 1);//将最后一个.删掉 System.out.println("删除之后"+st); String re = "^(255)\\." + "(1\\d{2}|2[0-4]\\d|25[0-5]|[1-9]\\d|\\d)\\." + "(1\\d{2}|2[0-4]\\d|25[0-5]|[1-9]\\d|\\d)\\." + "(1\\d{2}|2[0-4]\\d|25[0-5]|[1-9]\\d|\\d)$"; Pattern p = Pattern.compile(re); Matcher m = p.matcher(st); if(m.matches()){ System.out.println("子网掩码合法！"); } if(!m.matches()){ System.out.println("子网掩码非法！"); } break; } } return st; } }