为什么我在Java ArrayList中始终只获取最后一个对象值? [英] Why do I keep getting only tha last object value in Java ArrayList?
问题描述
我设法将所有对象放入arraylist，但无法打印所有值.无论使用哪种方法，只有最后一张都将被打印.
I have managed to put all objects into arraylist but I am not able to print all values. Only the last one is getting printed, regardless of method used.
它不是仅通过ArrayList打印，这让我想知道被推送的对象是否相同.
It is not getting printed through ArrayList only, which makes me wonder if the objects pushed are the same.
如果是，该如何更改?我已经附加了程序(运行FileInput.java):
If it is, how do I change that? I have attached the program (run 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";
}
*/
}
推荐答案
简单:
Player1 user = new Player1();
您要一次又一次添加相同对象.将该语句放入您的循环中.您想在每次循环迭代期间添加一个完全新的Playwer对象！
You are adding the same object again and again. Put that statement into your loop instead. You want to add a completely new Playwer object during each loop iteration!
但是即使那样，事情还是无法解决.因为(如Eran所言):您的Player类仅具有 static 字段.就像作弊"；因为这意味着所有Player对象也会看到相同字段(因为 static 字段在类的所有实例之间都是共享！)
But even then, things wouldn't work out; because (as Eran figured): your Player class has only static fields. That is like "cheating"; because it means that all Player objects would see the same fields, too (because static fields are shared between all instances of a class!)
换句话说:静态是良好的OO设计中的异常.您没有默认使用它.相反:您仅在特殊情况下使字段为静态(有关某些示例，请参见此处)
In other words: static is an abnormality in good OO design. You don't use it as default; to the contrary: you only make fields static in special corner cases (see here for some examples).
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