我目前正在用 Java 开发一款家庭恩怨游戏。我有一个名为 questions 的对象问题的数组列表，它存储在整个游戏中使用的随机问题。我试图以某种方式填充数组列表以确保没有重复项，但是它不起作用并且我收到了重复项。
初始化为字段的是我的问题数组列表:
private ArrayList<Question> questions = new ArrayList<>();
这是我目前正在尝试的:
//Populates questions list
for(int i=0; i<15; i++)
{
Question q = new Question();
//makes sure there are no duplicates
if(!questions.contains(q))
questions.add(q); //not working for some reason cry
System.out.println(q.getQuestion());
}
当我打印出问题时，我仍然得到重复的问题:
Name something you would see on the Jerry Springer show:
Name something that would get you thrown out of most bars:
What accent might an American pretend to have in order to sound more attractive:
Name a breed of dog that might be used as a guard dog:
Name a place where a child might get seperated from its parents:
Name something you would see on the Jerry Springer show:
Name something that would get you thrown out of most bars:
Name a place where a child might get seperated from its parents:
Name something for which you need a warranty:
Name a game that would be inappropriate at a company party:
Name something for which you need a warranty:
Name a place where a child might get seperated from its parents:
Name an activity that could be rained out:
Name something for which you need a warranty:
Name something that would get you thrown out of most bars:
我确实重写了我的问题类中的 equals 方法，但它并没有解决问题。这是我的问题类:
/**
* Question proposed to players to guess one of the answers on the board
*
* Each question has 5 possible answers
*
* The top answer to each question is stored at Answers(0) and is worth the most
* The last answer is stored at Answers(4) and is worth the least
*
*
* @author Stefan Gligorevic
*/
import java.util.ArrayList;
import java.util.Random;
import java.lang.String;
import java.lang.Object;
public class Question {
private ArrayList<Answer> answers;
private String question;
/**** MIGHT HAVE TO INITIALIZE ANSWERS TO AN ARRAY LIST WITH NO SIZE SO ADD CAN WORK ****/
//constructors
public Question(){
answers = new ArrayList<>();
question=getRandomQuestion();
}
//makes a random question with a set of answers
public String getRandomQuestion() {
String ask = "";
Random rand = new Random();
int n = 1 + rand.nextInt(10);
switch (n)
{
case 1:
ask="Name a place where a child might get seperated from its parents:";
answers.add(new Answer("Mall", 38));
answers.add(new Answer("Park", 23));
answers.add(new Answer("Zoo", 16));
answers.add(new Answer("Theme Park", 16));
answers.add(new Answer("Airport", 5));
break;
case 2:
ask="Name something for which you need a warranty:";
answers.add(new Answer("Car", 54));
answers.add(new Answer("TV", 23));
answers.add(new Answer("Watch", 8));
answers.add(new Answer("Computers", 4));
answers.add(new Answer("Appliance", 3));
break;
case 3:
ask="Name a fruit you can buy dried:";
answers.add(new Answer("Grape", 22));
answers.add(new Answer("Banana", 21));
answers.add(new Answer("Apricot", 21));
answers.add(new Answer("Prune", 17));
answers.add(new Answer("Apple", 15));
break;
case 4:
ask="Name an activity that could be rained out:";
answers.add(new Answer("Sports Event", 45));
answers.add(new Answer("Picnic", 34));
answers.add(new Answer("Wedding", 10));
answers.add(new Answer("Concert", 7));
answers.add(new Answer("Barbecue", 3));
break;
case 5:
ask="What accent might an American pretend to have in order to sound more attractive:";
answers.add(new Answer("French", 61));
answers.add(new Answer("British", 18));
answers.add(new Answer("Italian", 8));
answers.add(new Answer("Spanish", 8));
answers.add(new Answer("Australian", 3));
break;
case 6:
ask="Name a sport that might be played at a family reunion:";
answers.add(new Answer("Football", 54));
answers.add(new Answer("Baseball", 21));
answers.add(new Answer("Horseshoe", 8));
answers.add(new Answer("Frisbee", 7));
answers.add(new Answer("Basketball", 6));
break;
case 7:
ask="Name a game that would be inappropriate at a company party:";
answers.add(new Answer("Spin the Bottle", 41));
answers.add(new Answer("Strip Poker", 32));
answers.add(new Answer("Twister", 11));
answers.add(new Answer("Truth or Dare", 11));
answers.add(new Answer("Beer Pong", 3));
break;
case 8:
ask="Name something that would get you thrown out of most bars:";
answers.add(new Answer("Getting in a fight", 45));
answers.add(new Answer("Drinking too much", 29));
answers.add(new Answer("Not Paying", 6));
answers.add(new Answer("Stripping", 5));
answers.add(new Answer("Being underage", 3));
break;
case 9:
ask="Name something you would see on the Jerry Springer show:";
answers.add(new Answer("Fighting", 56));
answers.add(new Answer("Nudity", 22));
answers.add(new Answer("Security", 6));
answers.add(new Answer("Jerry Springer", 4));
answers.add(new Answer("Chairs Thrown", 3));
break;
case 10:
ask="Name a breed of dog that might be used as a guard dog:";
answers.add(new Answer("German Shepard", 36));
answers.add(new Answer("Pit Bull", 23));
answers.add(new Answer("Doberman Pinscher", 20));
answers.add(new Answer("Rottweiler", 8));
answers.add(new Answer("Bulldog", 5));
break;
default:
//won't reach this hehe
} //end switch
return ask;
}
@Override
public boolean equals(Object obj)
{
if(obj == null)
return false;
if(!Question.class.isAssignableFrom(obj.getClass()))
return false;
final Question q = (Question) obj;
if(q.getQuestion() == null || this.getQuestion() == null)
return false;
if(!this.getQuestion().equalsIgnoreCase(q.getQuestion()))
return false;
return true;
}
//getters and setters
public String getQuestion() { return question; }
public ArrayList<Answer> getAnswers() { return answers; }
//returns answer at given index
public Answer answerAt(int index) { return answers.get(index); }
//returns String of answer at specified index
public String getAnswerAt(int index) { return answers.get(index).getAnswer(); }
//returns point value of answer at specified index
public int getAnswerPoints(int index) { return answers.get(index).getValue(); }
//returns the points earned for this question
//points are the point values of all the answers that have been found
public int pointsEarned() {
int points=0;
for (int i=0; i<answers.size(); i++)
{
if(answers.get(i).isFound())
points += answers.get(i).getValue();
}
return points;
}
//Sets a particular answer's value
public void setAnswerVal(int index, int val) { answers.get(index).setValue(val); }
//Add a multiplier to each answer's value for the question
public void addMultiplier(int multiplier)
{
for(int i=0; i<answers.size(); i++)
{
int val = answers.get(i).getValue();
answers.get(i).setValue(multiplier * val);
}
}
//returns string of each answer
public String topAnswer() { return answers.get(0).getAnswer(); }
public String Answer2() { return answers.get(1).getAnswer(); }
public String Answer3() { return answers.get(2).getAnswer(); }
public String Answer4() { return answers.get(3).getAnswer(); }
public String lastAnswer() { return answers.get(4).getAnswer(); }
//returns values of each answer
public int topAnswerVal() { return answers.get(0).getValue(); }
public int Answer2Val() { return answers.get(1).getValue(); }
public int Answer3Val() { return answers.get(2).getValue(); }
public int Answer4Val() { return answers.get(3).getValue(); }
public int lastAnswerVal() { return answers.get(4).getValue(); }
}
我不明白为什么它不起作用:(非常感谢帮助!
最佳答案
您重写的 equals 方法逻辑很好。只是你正在做sysout在错误的地方让你相信逻辑不起作用。不要在添加问题的 for 循环内打印问题，而是在该循环外部打印它。像下面这样修改你的逻辑，你会得到预期的结果
for(int i=0; i<15; i++)
{
Question q = new Question();
//makes sure there are no duplicates
if(!questions.contains(q))
questions.add(q); //not working for some reason cry
}
for (Question question : questions) {
System.out.println(question.getQuestion());
}
请注意，每当您覆盖 equals 时方法，您应该覆盖 hashCode以及。因为如果你不这样做，那么 Object 中的默认实现将使用类。因此，即使根据 equals() 方法它们相等，它们也可能具有不同的哈希码。您正在使用Arraylist ，所以您在这里不会遇到问题，但会遇到一些集合，例如 HashSet, HashMap它同时使用 equals和hashcode用于添加和检索对象。这可能会给您带来意想不到的结果。因此，请始终一致地覆盖它们。 Link
public int hashCode(){
return question.hashCode();
}
此外，如果您的平等逻辑基于 String question只是，我建议您要么将您的 Question类工具Comparable或创建一个 Comparator为您Question类，而不是使用 ArrayList要保存问题列表，请使用 Set(TreeSet)这样 1)您不必担心实现 equals 和 hashcode 方法，2)您不必总是检查添加新问题。下面是代码片段
实现Comparable<Question>
@Override
public int compareTo(Question question) {
return this.getQuestion().compareTo(question.getQuestion());
}
向 Set 添加问题
Set<Question> questions = new TreeSet<>();
for(int i=0; i<15; i++)
{
questions.add(new Question());
}
for (Question question : questions) {
System.out.println(question.getQuestion());
}
关于java - 不允许数组列表中的对象重复，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/59597019/