为什么我一直只获得Java ArrayList中的最后一个对象值？

Question

我已设法将所有对象放入arraylist但我无法打印所有值.无论使用何种方法,都只打印最后一个.

它不是仅通过ArrayList打印,这让我想知道推送的对象是否相同. 

如果是,我该如何改变？我已经附加了程序(运行FileInput.java):

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.StringTokenizer;

import javax.swing.text.html.HTMLDocument.Iterator;

//lecture notes(L1) method
public class FileInput {
    static String first;
    static String second;
    static String third;
    static String fourth;
    static String fifth;
    static String sixth;

    static int num = 1;
        public static void main(String[] args)throws FileNotFoundException, IOException{
        Scanner input = new Scanner(new File("player.txt"));
        String data = null;

        PrintWriter output = new PrintWriter("outfile.txt");

        // Player1 user = new Player1();

        ArrayList<Player1>listOfPlayers = new ArrayList<>();

        Player1 user = new Player1();

        // Tokenizing
        System.out.println("CSCI213 Players Management System");
        while(input.hasNextLine()){

            System.out.println("\nPlayer " + num);
            data = input.nextLine();
            StringTokenizer token = new StringTokenizer(data,"|");

            // int t = token.countTokens();
            // System.out.println("t is:" + t);

            first = token.nextToken().trim();
            user.setLoginname(first);

            second = new String(token.nextToken("|"));
            user.setPassword(second);

            third = new String(token.nextToken("|"));
            user.setChips(third);

            fourth = new String(token.nextToken("|"));
            user.setUsername(fourth);

            fifth = new String(token.nextToken("|"));
            user.setEmail(fifth);

            sixth = new String(token.nextToken("|"));
            user.setBirthdate(sixth);

            // user.display();

            listOfPlayers.add(user);
            System.out.println("Size is: " + listOfPlayers.size());
            // System.out.println(user.loginname);
            // System.out.println(listOfPlayers.get(num-1).loginname);
            num++;
            // output.write(data);
            // output.write("\r\n");
        }
        int x = listOfPlayers.size();
        System.out.println("Size is: " + x);
        System.out.println(listOfPlayers);

        // Display address of required
        Player1 p = new Player1();

        for(int i = 0; i < x; i++){
            p = listOfPlayers.get(i);
            System.out.println(p.loginname);
        }

        for(Player1 e:listOfPlayers){
            System.out.println(e.loginname);
            System.out.println(e.email);
        }

        while(input.hasNextLine()){
            data = input.nextLine();
            output.write(data);
            output.write("\r\n"); 
        }

        input.close();
        output.close();
    }
}

// Store all player information
public class Player1 {
        static String loginname;
        static String password;
        static String chips;
        static String username;
        static String email;
        static String birthdate;

        /*
        public Player1(String loginname, String password, 
                String username, String email, String birthdate){
            this.loginname = loginname;
            this.password = password;
            this.username = username;
            this.email = email;
            this.birthdate = birthdate;
        }
        */

        public Player1() {
            // TODO Auto-generated constructor stub
        }

        public static String getLoginname() {
            System.out.print("loginname: ");
            return loginname;
        }

        public static void setLoginname(String loginname) {
            Player1.loginname = loginname;
        }

        public static String getPassword() {
            System.out.print("password: ");
            return password;
        }

        public static void setPassword(String password) {
            Player1.password = password;
        }

        public static String getUsername() {
            System.out.print("username: ");
            return username;
        }

        public static void setUsername(String username) {
            Player1.username = username;
        }

        public static String getEmail() {
            System.out.print("email: ");
            return email;
        }

        public static void setEmail(String email) {
            Player1.email = email;
        }

        public static String getBirthdate() {
            System.out.print("birthdate: ");
            return birthdate;
        }

        public static void setBirthdate(String birthdate) {
            Player1.birthdate = birthdate;
        }

        public static String getChips() {
            System.out.print("chips: ");
            return chips;
        }

        public static void setChips(String chips) {
            Player1.chips = chips;
        }

        public void display() {
            System.out.println("Name: " + this.username);
            System.out.println("Email: " + this.email);
            System.out.println("Birthdate: " + this.birthdate);
            System.out.println("Login ID: " + this.loginname);
            System.out.println("Balance Chips: " + this.chips);
        }
/*
        @Override
        public String toString() {
            return "toString()=" + this.loginname + "\n";
        }       
*/      
}

Answer 1

简单:

 Player1 user = new Player1();

您是一次又一次地添加相同的对象.将该语句放入循环中.要添加一个完全每次循环迭代中新Playwer对象!

但即便如此,事情也不会成功; 因为(正如Eran所说):你的Player类只有静态字段.那就像"作弊"; 因为这意味着所有Player对象也会看到相同的字段(因为静态字段在类的所有实例之间共享!)

换句话说:静态是良好OO设计中的异常.您不要将其用作默认值; 恰恰相反:你只在特殊的角落情况下使字段静态(参见这里的一些例子).