为什么不打印对象内部的字符串?

Question

此程序用于闪存卡应用程序。我的构造函数使用了一个链表，但问题是，当我使用一个方法列出特定盒子中的卡片时，它不会打印期望的结果。系统应该打印"瑞恩·哈丁"。而是打印"Box$NoteCard@68e86f41"。有人能解释为什么会发生这种情况，我能做些什么来解决这个问题吗?我还附上了我的盒子和卡片类。

import java.util.LinkedList;
import java.util.ListIterator;
public class Box {
public LinkedList<NoteCard> data;
public Box() {
    this.data = new LinkedList<NoteCard>();
}
public Box addCard(NoteCard a) {
    Box one = this;
    one.data.add(a);
    return one;
}
public static void listBox(Box a, int index){
    ListIterator itr = a.data.listIterator();
    while (itr.hasNext()) {
        System.out.println(itr.next());
    }
}
public static void main(String[] args) {
    NoteCard test = new NoteCard("Ryan", "Hardin");
    Box box1 = new Box();
    box1.addCard(test);
    listBox(box1,0);
}
}

这是我的NoteCard类

public class NoteCard {
public static String challenge;
public static String response;

public NoteCard(String front, String back) {
    double a = Math.random();
    if (a > 0.5) {
        challenge = front;
    } else
        challenge = back;
    if (a < 0.5) {
        response = front;
    } else
        response = back;
}

public static String getChallenge(NoteCard a) {
    String chal = a.challenge;
    return chal;
}
public static String getResponse(NoteCard a) {
    String resp = response;
    return resp;
}
public static void main(String[] args) {
    NoteCard test = new NoteCard("Ryan", "Hardin");
    System.out.println("The challenge: " + getChallenge(test));
    System.out.println("The response: " + getResponse(test));
}
}

Answer 1

尝试在class NoteCard中重写toString()方法。

@Override
public String toString()
{
  //Format your NoteCard class as an String
  return noteCardAsString;
}

Answer 2

首先你使用了太多的static keyword。我不确定你是否需要那个。
无论如何，创建两个实例变量front和back，并在NoteCard类的构造函数中为其赋值，同时实现toString方法

public class NoteCard {
public static String challenge;
public static String response;
public String front;
public String back;

public NoteCard(String front, String back) {
 //your code
 this.front = front;
 this.back = back;
}
@Override
public String toString()
{
  //return "The challenge:" + challenge + " " + "The response: " + response;
  return "The Front:" + front + " " + "The Back: " + back;
}

注意:由于实例方法toString()是隐式继承的将toString()方法声明为子类型中的静态方法导致编译时错误，所以不要将此方法设为STATIC