The road from my heart to java chapter2

public class MaoPao {

public static void main(String[] args) {

int[] arr = { 12, 3, 23, 1, 5 };

int len = arr.length-1;

for (int i = 0; i < len; i++) {

for (int j = 0; j < len - i; j++) {

if(arr[j] < arr[j+1]){

int temp = arr[j];

arr[j] = arr[j+1];

arr[j+1] = temp;

}

}

}

for(int i : arr){

System.out.println(i);

}

}

}

public class Library {

public static void main(String[] args){

java.util.Scanner input = new java.util.Scanner(System.in);

String[] names = new String[10];

String[] passwords = new String[10];

while(true){

System.out.println("   欢迎登录！");

System.out.println("***************");

System.out.println("   1.用户注册");

System.out.println("   2.用户登录");

System.out.println("   3.退出");

String num = input.next();

if("1".equals(num)){

System.out.println("用户注册！");

System.out.print("请输入用户名：");

String regName = input.next();

boolean bool = true;

for(String item : names){

if(regName.equals(item)){

System.out.println("该用户名已存在！");

bool = false;

break;

}

}

if(bool){

System.out.print("请输入密码：");

String regpassword = input.next();

for(int i = 0; i < names.length; i++){

if(names[i] == null){

names[i] = regName;

passwords[i] = regpassword;

}

}

System.out.println("注册成功！");

}

}else if("2".equals(num)){

System.out.println("用户登录：");

System.out.print("请输入用户名：");

String logName = input.next();

System.out.print("请输入密码：");

String logPassword = input.next();

boolean bool2 = false;

for(int i = 0; i < names.length; i++){

if(logName.equals(names[i]) && logPassword.equals(passwords[i])){

bool2 = true;

break;

}

}

if(bool2){

System.out.println("登录成功！");

}else{

System.out.println("用户名或密码错误！");

}

}

else if("3".equals(num)){

System.out.println("系统退出！");

break;

}else {

System.out.println("请输入正确编号！");

}

}

}

}