我有以下两个课程:
import java.io.*;
import java.util.*;
public class User {
public static String nickname;
public static String ipAddress;
public static ArrayList<String> listOfFiles;
public static File sharedFolder;
public static String fileLocation;
public User(String nickname, String ipAddress, String fileLocation) {
this.nickname = nickname.toLowerCase();
this.ipAddress = ipAddress;
Scanner userTyping = new Scanner(System.in);
fileLocation = userTyping.nextLine();
sharedFolder = new File(fileLocation);
}
public static List<String> fileList() {
File[] files = sharedFolder.listFiles();
listOfFiles = new ArrayList<String>();
for (int i = 0; i < files.length; i++) {
listOfFiles.add(i, files[i].toString().substring(fileLocation.length()));
System.out.println(listOfFiles.get(i));
}
return listOfFiles;
}
@Override
public String toString() {
return nickname + " " + ipAddress;
}
}
下一个:
import java.util.*;
public class UserCollector {
static List<User> allUsers;
public static void addUserToTheList() {
Scanner keyboardInput = new Scanner(System.in);
System.out.println("Type nickname: ");
String nickname = keyboardInput.nextLine();
System.out.println("Type IP: ");
String ipAddress = keyboardInput.nextLine();
System.out.println("Type File Location: ");
String fileLocation = keyboardInput.nextLine();
System.out.println("User that is attempting to log in is: "+ nickname + " and his IP is: " + ipAddress);
User inputUser = new User(nickname, ipAddress, fileLocation);
allUsers = new ArrayList<User>();
if (keyboardInput.nextLine().equalsIgnoreCase("INSERT") && !allUsers.contains(inputUser)) {
allUsers.add(inputUser);
System.out.println("User has been successfully added to your list.");
}
else
System.out.println("This user already exists on the list!");
}
public static void currentStateOfTheList() {
for (User u : allUsers) {
System.out.println("nick: "+u.nickname +", ip: "+ u.ipAddress );
}
}
public static void main(String[] args) {
UserCollector.addUserToTheList();
UserCollector.currentStateOfTheList();
}
}
现在,addUserToTheList() 方法的想法很简单。将 User 类型的对象添加到 ArrayList 中。也可以通过在控制台中输入昵称、ipAddress 和 fileLocation 来实现。我第一次运行它时,它运行良好,但它抛出了一个异常(NullPointer)。现在,当我运行它时,它编译得很好,但它说我已经在列表中拥有该用户,尽管我总是给出不同的昵称/ipAddress/fileLocation。
我相信用户对象有问题,每次我尝试运行它时都可能保持不变。
我希望有人帮助我。谢谢