关于哈希图的问题

Question

这是我的代码，这是我第一次使用HashMap。 我真的不明白为什么在将值分配给键"d"后会更改键"a"的值。似乎每次我为另一个键分配值时，键"a"的值都会被重写。

import java.util.HashMap;
import java.io.*;
class BowlingSystem {
static HashMap<String, BowlingSystem> bs=new HashMap();//abbreviate for Bowling System
public String Name;
public int no_game;//same as above
public String[] date;
public int total_score=0;
public String last_date;
public int last_score;
public int[] score;
public BowlingSystem(String Name_i, String[] date_i, int[] score_i){
score=score_i;
Name=Name_i;
date=date_i;
}
public void register (BowlingSystem information){
bs.put(information.Name,information);
}
public void out(String input){
if (bs.containsKey(input)) {
BowlingSystem information=(BowlingSystem)bs.get(input);
no_game=information.date.length-1;
last_date=information.date[no_game];
last_score=information.score[no_game];
for(int i=1;i<=no_game;i++){
total_score=total_score+score[i];
}
double avg=(double)total_score/no_game;
System.out.println("Name is "+information.Name+"n");
System.out.println("Number of games is "+no_game+"n");
System.out.println("Average score of all of the games is "+avg+"n");
System.out.println("The score of the last game is "+last_score+"n");
System.out.println("The date of the last game is "+information.date[no_game]+"n");
}
}
}
public class Homework06 {
public static void main(String [] args) throws IOException{
int[] scores=new int[5];
String[] dates=new String[5];
for (int i=1;i<=4;i++){//test data
scores[i]=20+i;
dates[i]="01/"+i+"/2017";
}
BowlingSystem a01=new BowlingSystem("a",dates,scores);
a01.register(a01);
for (int i=1;i<=4;i++){//test data
scores[i]=30+i;
dates[i]="02/"+i+"/2017";
}
BowlingSystem b01=new BowlingSystem("b",dates,scores);
b01.register(b01);
for (int i=1;i<=4;i++){//test data
scores[i]=40+i;
dates[i]="03/"+i+"/2017";
}
BowlingSystem c01=new BowlingSystem("c",dates,scores);
c01.register(c01);
for (int i=1;i<=4;i++){//test data
scores[i]=20+i;
dates[i]="05/"+i+"/2017";
}
BowlingSystem d01=new BowlingSystem("d",dates,scores);
d01.register(d01);
a01.out("a");//the outcome of this now is same as key "d"
b01.out("b");//the outcome of this now is same as key "d"
System.out.println("Please type in the name, in this case name is just a letter in lower case from a to d.n");//below this line is not important
BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in), 1);
String name=stdin.readLine(); 
}
}

Answer 1

所有BowlingSystem实例(Map的值)都引用传递给其构造函数(dates和scores)的相同数组，因此修改数组的内容会影响所有这些数组。

为了避免这种情况，您的BowlingSystem应该复制传递给它的数组，或者您应该将不同的数组传递给您正在创建的每个实例。

例如

取代

BowlingSystem a01=new BowlingSystem("a",dates,scores);

跟

BowlingSystem a01=new BowlingSystem("a",new String[5],new int[5]);

并对每个构造函数调用执行相同的操作。

Answer 2

这是因为HashMap中所有键的dates和scores都相同。这就是为什么当您打印出数据时，会显示最后添加到dates和scores的数据。