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  1. import java.util.*;
  2.  
  3. class Book implements Comparable<Book>, Cloneable {
  4.   /* private */ String title;
  5.   /* private */ Date publishDate;
  6.   /* private */ String comment;
  7.  
  8.   public boolean equals(Object obj) {
  9.     if(obj == this) return true;
  10.     if(obj == null) return false;
  11.     if(!(obj instanceof Book)) return false;
  12.     Book result = (Book) obj;
  13.     if((this.title == null && result.title == null)
  14.       && (this.publishDate == null || result.publishDate == null)) return true;
  15.     else if((this.title == null || result.title == null)
  16.       || (this.publishDate == null || result.publishDate == null)) return false;
  17.     else if(!result.title.equals(this.title)) return false;
  18.     else if(!result.publishDate.equals(this.publishDate)) return false;
  19.     else return true;
  20.   }
  21.  
  22.   public int hashCode() {
  23.     int hash = 1;
  24.     hash = hash * 31 + title.hashCode();
  25.     hash = hash * 31 + publishDate.hashCode();
  26.     return hash;
  27.   }
  28.  
  29.   public int compareTo(Book obj) {
  30.     return this.publishDate.compareTo(obj.publishDate);
  31.   }
  32.  
  33.   public Book clone() {
  34.     Book result = new Book();
  35.     result.title = this.title;
  36.     result.comment = this.comment;
  37.     result.publishDate = (Date) this.publishDate.clone();
  38.     return result;
  39.   }
  40. }
  41.  
  42. public class Main {
  43.   public static void main(String[] args) {
  44.     Book book1 = new Book();
  45.     book1.title = "本1";
  46.     book1.publishDate = new Date(1);
  47.     Book book2 = new Book();
  48.     book2.title = "本1";
  49.     book2.publishDate = new Date(1);
  50.     boolean bool1 = book1.equals(book2);
  51.     System.out.println(bool1);
  52.  
  53.     Book book3 = new Book();
  54.     book3.title = "本2";
  55.     book3.publishDate = new Date(1);
  56.     Book book4 = new Book();
  57.     book4.title = "本2";
  58.     boolean bool2 = book3.equals(book4);
  59.     System.out.println(bool2);
  60.  
  61.     Book book5 = new Book();
  62.     Book book6 = new Book();
  63.     boolean bool3 = book5.equals(book6);
  64.     System.out.println(bool3);
  65.  
  66.     Book book7 = new Book();
  67.     book7.title = "本3";
  68.     book7.publishDate = new Date(1);
  69.     Book book8 = new Book();
  70.     book8.publishDate = new Date(1);
  71.     boolean bool4 = book7.equals(book8);
  72.     System.out.println(bool4);
  73.   }
  74. }
Success #stdin #stdout 0.09s 27632KB
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https://ideone.com/e2hyln
language:
Java (HotSpot 12)
created:
6 years ago
visibility:
public

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