这可能有点复杂，但我会尽力解释
好吧，让我先把我的 CDList 类
* MAIN: *现在这是主程序问我的问题 主程序是测试 CDList 功能。您可以硬编码 5 次调用 add，然后 add() 将提示用户输入。您的主程序应该调用所有 CDlist 公共方法，并生成带标签的输出，清楚地解释 Page 2 of 2 输出试图演示的内容。这就是我到目前为止所拥有的 main ......只是为了测试 CDList 中的 add 方法......
输出： 这个程序的输出是一个完整的捕获测试会话，主程序产生标签说，“测试删除：”（或其他），然后显示结果。让评分员清楚地看到结果。您要 1) 将 5 张 CD（具有合理数据，每张至少 3 首曲目）添加到 CDList，2) 显示按艺术家排序的数据，3) 显示按标题排序后的列表，以及 4) 显示之前的列表并在从列表中删除其中一张 CD 之后。要获得满分，输出必须清楚地标记，CD 列表显示必须整洁且易于阅读。
编辑 5：我的 CDList 类
package cd;
import java.util.Scanner;
public class CDList {
public int cdnum;
private CD[] CDlist;
private int front, rear;
//private String artist;
//private String title;
public CDList(int size) {
CDlist = new CD[size];
cdnum = 0;
front = 0;
rear = size - 1;
}
public boolean add() {
boolean result = false;
Scanner input = new Scanner(System.in);
System.out.println("Please enter the Artist name and the CD title: ");
CD yourCD = new CD(input.nextLine(), input.nextLine());
System.out.println("Enter the number of songs: ");
int songNum = input.nextInt();
System.out.println("Enter the name of the songs: ");
for (int i = 0; i <= songNum; i++) {
yourCD.addTrack(input.nextLine());
}
CDlist[cdnum] = yourCD;
if (rear == front) {
result = false;
} else {
if (CDlist[rear] != null) {
rear--;
} else {
CDlist[rear] = yourCD;
}
result = true;
}
return result;
}
public void delete() {
Scanner deleteInput = new Scanner(System.in);
System.out.println("Which artist you would like to delete? ");
System.out.println("Enter artist name and title to be deleted:");
String artist = deleteInput.nextLine();
String title = deleteInput.nextLine();
for (int i = 0; i <= CDlist.length - 1; i++) {
if ((CDlist[i].getArtist().equals(artist))
&& (CDlist[i].getTitle().equals(title))) {
System.out.println("Found: " + CDlist[i].getArtist());
System.out.println(CDlist[i].getTitle());
if (deleteInput.nextInt() == 1) {
CDlist[i] = null;
cdnum--;
}
} else {
System.out.println("CD not found in the list.");
}
}
}
public void SortArtist() {
CD temp = new CD(" "," ");
for (int i = 0; i <= CDlist.length; i++) {
if (i < CDlist.length-1) {
if (CDlist[i].getArtist().compareTo(CDlist[i+1].getArtist())<0){
temp = CDlist[i];
CDlist[i] = CDlist[i + 1];
CDlist[i + 1] = temp;
}
}
}
}
public void SortTitle() {
CD temp1 ;
for (int i = cdnum; i > 0; i--) {
int x = 0;
for (int j = 1; j <= i; j++) {
if (CDlist[i].getTitle().compareTo(CDlist[i+1].getTitle())<0) {
x = j;
}
}
temp1 = CDlist[x];
CDlist[x] = CDlist[i];
CDlist[i] = temp1;
}
}
public void Display() {
for (int i = 0; i <= cdnum; i++) {
while (CDlist[i] == null) {
i++;
}
CDlist[i].display();
}
}
public int size() {
return cdnum;
}
}
输出错误：
是否要添加新CD 请输入艺术家姓名和CD 标题：eminem recovery 输入歌曲数量：3 输入歌曲名称：空间有限 不怕爱你说谎的方式 请输入艺术家姓名和CD 标题：micheal jackson 惊悚片 输入歌曲数量：3 输入歌曲名称：beat it 惊悚片 baby be mine 请输入艺术家姓名和 CD 标题：sean paul tomahawk technology 输入歌曲数量：3 输入名称歌曲：她不介意放在你身上 请输入艺术家姓名和CD名称：Manafest Glory 输入歌曲数量：3 输入歌曲名称：你在哪里失控的梦想 请输入艺术家姓名和 CD 标题：kj-52 合作 输入歌曲数量： 3 输入歌曲名称：亲爱的苗条 你在哪里 为什么
cd.Main.main(Main.java:17) 处 cd.CDList.SortArtist(CDList.java:86) 处的线程“main”java.lang.NullPointerException 异常 Java 结果：1
这是第 86 行： if (CDlist[i].getArtist().compareTo(CDlist[i+1].getArtist())<0)
第 17 行和第 17 行：list.SortArtist();
主要的
package cd;
public class Main {
public static void main(String[] args) {
System.out.println("Would you like to add a new CD");
CDList list = new CDList(5);
for (int i = 0; i < 5; i++) {
list.add();
}
list.SortArtist();
list.Display();
list.SortTitle();
list.Display();
list.delete();
list.Display();
}
}
EDIT3：我的 CD 课
package cd;
公开课 CD {
private String artist; //stores artist name
private String title; //stores CD title
private String track;
private tracklist list; //tracklist variable
// constructor, sets artist and title, creates tracklist array
public CD(String artistname, String titlename) {
artist = artistname;
title = titlename;
list = new tracklist();
}
public String getArtist() {
return artist;
}
public String getTitle() {
return title;
}
// adds a new track, return true if less than 100, flase if no space
public boolean addTrack(String trackinfo) {
if (list.count < 100) {
list.add(trackinfo);
return true;
} else {
return false;
}
}
public int numTracks() {
return list.count;
}
public void display() {
System.out.println("Artist: \t" + artist);
System.out.println("CD Title: \t" + title);
list.display(5);
}
}
EDIT4：曲目列表类
package cd;
public class tracklist {
public String[] lists; //array
private String tNum;
private String tName;
int numElements; // Counter to keep track of the used slots
int count; //loop counter
// constructor, creats array for tracks
public tracklist() {
numElements = 0;
lists = new String[100];
}
// adds tracks to tracklist
public boolean add(String track) {
if (numElements < 100) {
lists[numElements] = track;
numElements++;
return true;
} else {
System.out.println("The tracklist is full.");
return false;
}
}
//returns the number of elements in array
public int count() {
return numElements;
}
//displays tracklist in required form
public void display(int indent) {
tName = "%" + indent + "s";
tNum = "%" + (indent - 2) + "d";
System.out.printf(tName, "Track #");
System.out.println("\t\tSong Title");
for (count = 0; count < numElements; count++) {
System.out.printf(tNum, count + 1);
System.out.println("\t\t" + lists[count]);
}
}
}