我从Java教科书中获得了一项任务，按字母顺序对CD名称数组进行排序。作业说：
更改Tunes程序（清单6.7），以便它按照标题对CD进行排序。使用本章Sorts类中定义的常规对象排序。
这是清单6.7：
//********************************************************************
// Tunes.java Author: Lewis/Loftus/Cocking
//
// Driver for demonstrating the use of an array of objects.
//********************************************************************
public class Tunes {
//-----------------------------------------------------------------
// Creates a CDCollection object and adds some CDs to it. Prints
// reports on the status of the collection.
//-----------------------------------------------------------------
public static void main (String[] args) {
CDCollection music = new CDCollection ();
music.addCD ("By the Way", "Red Hot Chili Peppers", 14.95, 10);
music.addCD ("Come On Over", "Shania Twain", 14.95, 16);
music.addCD ("Soundtrack", "The Producers", 17.95, 33);
music.addCD ("Play", "Jennifer Lopez", 13.90, 11);
System.out.println (music);
music.addCD ("Double Live", "Garth Brooks", 19.99, 26);
music.addCD ("Greatest Hits", "Stone Temple Pilots", 15.95, 13);
System.out.println (music);
}
}
我不确定如何按字母顺序使用字母进行排序。我确实创建并将CD组织成一组数字，只是为了看它的外观：
//********************************************************************
// Tunes.java Author: Lewis/Loftus/Cocking
//
// Driver for demonstrating the use of an array of objects.
//********************************************************************
public class Tunes {
//-----------------------------------------------------------------
// Creates a CDCollection object and adds some CDs to it. Prints
// reports on the status of the collection.
//-----------------------------------------------------------------
public static void main (String[] args) {
CDCollection[] music = new CDCollection[5];
music[0] = new CDCollection ("By the Way", "Red Hot Chili Peppers", 14.95, 10);
music[1] = new CDCollection ("Come On Over", "Shania Twain", 14.95, 16);
music[2] = new CDCollection ("Soundtrack", "The Producers", 17.95, 33);
music[3] = new CDCollection ("Play", "Jennifer Lopez", 13.90, 11);
System.out.println (music);
music[4] = new CDCollection ("Double Live", "Garth Brooks", 19.99, 26);
music[5] = new CDCollection ("Greatest Hits", "Stone Temple Pilots", 15.95, 13);
System.out.println (music);
}
}
这是包含选择和插入排序方法的排序类：
//********************************************************************
// Sorts.java Author: Lewis/Loftus/Cocking
//
// Demonstrates the selection sort and insertion sort algorithms,
// as well as a generic object sort.
//********************************************************************
public class Sort {
//-----------------------------------------------------------------
// Sorts the specified array of integers using the selection
// sort algorithm.
//-----------------------------------------------------------------
public static void selectionSort (int[] numbers) {
int min, temp;
for (int index = 0; index < numbers.length-1; index++) {
min = index;
for (int scan = index+1; scan < numbers.length; scan++)
if (numbers[scan] < numbers[min])
min = scan;
// Swap the values
temp = numbers[min];
numbers[min] = numbers[index];
numbers[index] = temp;
}
}
//-----------------------------------------------------------------
// Sorts the specified array of integers using the insertion
// sort algorithm.
//-----------------------------------------------------------------
public static void insertionSort (int[] numbers) {
for (int index = 1; index < numbers.length; index++) {
int key = numbers[index];
int position = index;
// shift larger values to the right
while (position > 0 && numbers[position-1] > key) {
numbers[position] = numbers[position-1];
position--;
}
numbers[position] = key;
}
}
//-----------------------------------------------------------------
// Sorts the specified array of objects using the insertion
// sort algorithm.
//-----------------------------------------------------------------
public static void insertionSort (Comparable[] objects) {
for (int index = 1; index < objects.length; index++) {
Comparable key = objects[index];
int position = index;
// shift larger values to the right
while (position > 0 && objects[position-1].compareTo(key) > 0) {
objects[position] = objects[position-1];
position--;
}
objects[position] = key;
}
}
}
我只是不确定如何使用字母而不是数字进行排序。提前感谢您的帮助。
答案 0 :(得分：1)
实现这一目标的方法是Sort#insertionSort(Comparable[])。
String提供方法String#compareTo(String)，因为它实现了接口Comparable<String>。创建此方法的方式是按字典顺序对字符串进行排序。
所以简单地将数组传递给Sort#insertionSort(Comparable[])应该可以解决问题。如何工作应在后面的书中解释（至少我希望如此）。
答案 1 :(得分：1)
您可以在compareTo方法中实现Comparable接口并比较Title，然后Collections.sort（）将为您解决问题：
public class CDItem implements Comparable<CDItem>{
String title;
String singer;
double price;
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getSinger() {
return singer;
}
public void setSinger(String singer) {
this.singer = singer;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
CDItem(String title, String singer, double price){
this.title=title;
this.singer=singer;
this.price=price;
}
@Override
public int compareTo(CDItem item){
return this.title.compareTo(item.title);
}
}
public class CDCollection{
List<CDItem> list=new ArrayList<CDItem>();
public void addCD(String title, String singer, double price){
CDItem item=new CDItem(title, singer, price);
list.add(item);
}
public String toString(){
String result="";
for(int i=0; i<list.size(); i++){
CDItem item=(CDItem)list.get(i);
result=result + "|" + item.getTitle();
}
return result;
}
public void sort(){
Collections.sort(list);
}
}
然后在Tunes类中添加最后两行：
public class Tunes {
public static void main(String[] args) {
CDCollection music = new CDCollection ();
music.addCD ("By the Way", "Red Hot Chili Peppers", 14.95);
music.addCD ("Come On Over", "Shania Twain", 14.95);
music.addCD ("Soundtrack", "The Producers", 17.95);
music.addCD ("Play", "Jennifer Lopez", 13.90);
System.out.println (music);
music.addCD ("Double Live", "Garth Brooks", 19.99);
music.addCD ("Greatest Hits", "Stone Temple Pilots", 15.95);
System.out.println (music);
music.sort();
System.out.println (music);
}
}