[OCPJP]集合的排序

Given the code fragments:

public class Book implements Comparator<Book> {
String name;
double price;
public Book() {
}
public Book(String name, double price) {
this.name = name;
this.price = price;
}
public int compare(Book b1, Book b2) {
return b1.name.compareTo(b2.name);
}
public String toString() {
return name + ":" + price;
}
}

public class Book implements Comparator<Book> {

String name;

double price;

public Book() {

}

public Book(String name, double price) {

this.name = name;

this.price = price;

}

public int compare(Book b1, Book b2) {

return b1.name.compareTo(b2.name);

}

public String toString() {

return name + ":" + price;

}

and

List<Book> books = Arrays.asList(new Book("Beginning with Java", 2), new Book("A Guide to Java Tour", 3));
Collections.sort(books, new Book());
System.out.print(books);

List<Book> books = Arrays.asList(new Book("Beginning with Java", 2), new Book("A Guide to Java Tour", 3));

Collections.sort(books, new Book());

System.out.print(books);

What is the result?

[A Guide to Java Tour:3.0, Beginning with Java:2.0]

[Beginning with Java:2.0, A Guide to Java Tour:3.0]

C. A compilation error occurs because the Book class does not override the abstract method compareTo().
D. An Exception is thrown at run time.

題解

Book類別實作了Comparator介面，並使用Book物件的name欄位的字串辭典順序來作為排序的依據。

程式第36行，使用了Collections類別的sort方法並傳入Book這個Comparator物件來排序集合物件。

由於A的辭典順序在B的前面，因此排序之後會輸出：

[A Guide to Java Tour:3.0, Beginning with Java:2.0]

MagicLen

[OCPJP]集合的排序

題解

關於作者

Magic Len

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