该类型必须实现继承的抽象方法

Question

我正在开发一个中级 Java 程序，我觉得我的逻辑是正确的，但是我在课程介绍中遇到了这个错误：

类型 QuestionSet 必须实现继承的抽象方法 IQuestionSet.add(IQuestion)

我确实有方法，但我有一个参数的 Question 对象而不是 IQuestion(The Interface for Question)

问题集：

package com.jsoftware.test;

import java.io.Serializable;
import java.util.ArrayList;

public class QuestionSet implements Serializable, IQuestionSet{

    ArrayList<Question> test = new ArrayList<Question>();

    public QuestionSet emptyTestSet(){
        QuestionSet set = new QuestionSet();
        return set;
    }
    public QuestionSet randomSample(int size){
        QuestionSet set = new QuestionSet();
        if(size>test.size()-1){
            for(int i =1; i<test.size(); i++){
                int num = (int)(Math.random()*test.size());
                set.add(test.get(num));
            }
        }else{
            for(int i =1; i<size; i++){
                int num = (int)(Math.random()*test.size());
                set.add(test.get(num));
            }
        }
        return set;
    }
    public boolean add(Question q){
        try{
            test.add(q);
            return true;
        }catch(Exception e){
            return false;
        }
    }
    public boolean remove(int index){
        try{
            test.remove(index);
            return true;
        }catch(Exception e){
            return false;
        }
    }
    public Question getQuestion(int index){
        return test.get(index);
    }
    public int size(){
        return test.size();
    }


}

IQuestionSet：

package com.jsoftware.test;

/**
 * This interface represents a set of question. 
 * 
 * @author thaoc
 */
public interface IQuestionSet {

    /**
     * Create an empty test set.
     * @return  return an instance of a test set.
     */
    public IQuestionSet emptyTestSet();

    /**
     * return a test set consisting of a random questions.
     * @param size The number of random questions.
     * @return The test set instance containing the random questions.
     */
    public IQuestionSet randomSample(int size);

    /**
     * add a question to the test set.  
     * @param question The question
     * @return True if successful.
     */
    public boolean add(IQuestion question);

    /**
     * 
     * @param index Remove question using index
     * @return  true if index is valid
     */
    public boolean remove(int index);

    /**
     * Retrieving a question using an index
     * @param index
     * @return the question if index is valid, null otherwise.
     */
    public IQuestion getQuestion(int index);

    /**
     * Return the number of questions in this test set.
     * @return number of questions.
     */
    public int size();
}

Answer 1

首先将问题列表更改为使用 IQuestion 类型：

ArrayList<IQuestion> test = new ArrayList<IQuestion>();

然后更改方法声明：

public boolean add(IQuestion q){
    try{
        test.add(q);
        return true;
    }catch(Exception e){
        return false;
    }
}