字符串相关
字符串对比
字符串相关方法
用户登录
定义user类保存用户信息
public class user {private String name;private String mima;public void setname(String name){this.name=name;}public String getname(){return name;}public void setmima(String mima){this.mima=mima;}public String getmima(){return mima;}public user(String name,String mima){this.name=name;this.mima=mima;}
}zhen类代表已有的用户信息（用来对比）
public class zhen {user u1=new user("fds669","669");user u2=new user("fds668","668X");user u3=new user("fds667","667x");//存储三个用户信息String [][]User={{u1.getname(),u1.getmima()},{u2.getname(),u2.getmima()},{u3.getname(),u3.getmima()}};public String[][] f(){return User;}
}duibi类，对比name和mima
public class duibi {zhen Z=new zhen();String [][]arr=Z.f();int a=-1;public int duibiname(String x){int flage=0;for(int i=0;i<arr.length;i++){if(arr[i][0].equals(x)){flage++;a=i;}}return flage;}public int duibimima(String x){int flage=0;if(a==-1){return -1;//不存在该用户}else{if(arr[a][1].equals(x)){flage++;}}return flage;}
}Denglu类
import java.util.Scanner;
public class Denglu {Scanner sc=new Scanner(System.in);duibi d=new duibi();String a,b;public void denglu(){int count =1;//记录输入次数while (count <= 3) {System.out.print("请输入用户名: ");a = sc.next();System.out.print("请输入密码: ");b = sc.next();int x = d.duibiname(a);int y = d.duibimima(b);if (x == 0) {if (count == 3) {System.out.println("超出三次无法输入，账户已被锁定");} else {System.out.println("不存在该用户");count++;}} else if (y == 0) {if (count == 3) {System.out.println("超出三次无法输入，账户已被锁定");} else {System.out.println("密码输入错误");count++;}} else {System.out.println("登录成功！！！");break;}}}}
测试主函数
public class test {public static void main(String[]args){Denglu f=new Denglu();f.denglu();}
}
测试结果
遍历字符串
/*案例 遍历字符串
需求：键盘录入一个字符串，使用程序实现在控制台遍历该字符串*/
import java.util.Scanner;
public class test3 {public static void main(String[]args){Scanner sc=new Scanner(System.in);String a;System.out.println("请输入字符串a：");a=sc.next();for(int i=0;i<a.length();i++)System.out.print(a.charAt(i));}
} 
拼接字符串
/*定义一个方法，把int数组中的数据按照指定的格式拼接成一个字符串返回，
调用该方法，并在控制台输出结果。
例如：
数组为intarr={1,2,3);
执行方法后的输出结果为：[1,2,3]*/
//StringBuilder 对象名称 = new StringBuilder();
public class test4 {public static String f(int []arr){StringBuilder a = new StringBuilder();int b=arr.length+2+(arr.length-1);a.append('[');for(int i = 0; i<arr.length; i++){/*i位置是数字j位置是，【】提前定义好*/a.append(arr[i]);if(i<arr.length-1){a.append(',');}}a.append(']');return a.toString();}public static void main(String[]args){int []arr={1,2,3,34,214,234,132,23,23,32,4,23,};System.out.println(f(arr));}
}
//StringBuilder 类
//a.append();将指定的字符串追加到此字符序列。 
金额转换
//金额转换
public class test5 {public static StringBuilder zhuan(int x){char a[]={'零','壹','贰','叁','肆','伍','陆','柒','捌','玖'};char b[]={'元','拾','佰','仟','万'};int c,d=0;StringBuilder arr=new StringBuilder();while(x>0){c=x%10;for(int i=0;i<a.length;i++){if (i == c) {
// arr.append(b[(d++)%5]);arr.append(b[d++]);arr.append(a[c]);}}x/=10;}return arr.reverse();}public static void main(String[]args){System.out.println(zhuan(6789));//只能转换 1-99999}
}
手机号屏蔽
//屏蔽手机号码
//15536714033
//155****4033
import java.util.Scanner;
public class test6 {public static char[] f(String x){char []a=new char[x.length()];for(int i=0;i<x.length();i++){a[i]=x.charAt(i);if(i==3||i==4||i==5||i==6)a[i]='*';}return a;}public static void main(String[]args){Scanner sc=new Scanner(System.in);String number;System.out.println("请输入手机号");number=sc.next();System.out.println(f(number));}
} 
身份证信息查看
/*
身份证信息查看
7-14位：.出生年，月，日
17位：性别*/
import java.util.Scanner;
public class test7 {public static void f(String x){//StringBuilder years = null,month= null,day= null;StringBuilder years = new StringBuilder();StringBuilder month = new StringBuilder();StringBuilder day = new StringBuilder();char xingbie;// 提取出生年份（第7 - 10位）for (int i = 6; i <= 9; i++) {years.append(x.charAt(i));}// 提取出生月份（第11 - 12位）for (int i = 10; i <= 11; i++) {month.append(x.charAt(i));}// 提取出生日期（第13 - 14位）for (int i = 12; i <= 13; i++) {day.append(x.charAt(i));}if((x.charAt(16)-'0')%2!=0)xingbie='男';//男elsexingbie='女';//女
// System.out.print(years+"年");
// System.out.print(month+"月");
// System.out.print(day+"日");
// System.out.print("性别是"+xingbie);System.out.println(years.toString()+"年"+month.toString()+"月"+day.toString()+"日"+"性别是"+xingbie);}public static void main(String[]args){Scanner sc=new Scanner(System.in);String id;System.out.println("请输入身份证号码：");id=sc.next();if(id.length()!=18)System.out.println("输入不合法");elsef(id);}
