Need to write a equals-method to check if a book is the same as another book but one book contains m-CodePudding

Below is my code at this moment, I need to add to the equals method so when I create a two books they will only be equal if both of the attributes are the same. Hopefully you guys can help.

public class Book {
    private String title;
    private boolean bound;

    Book(String title, boolean bound) {
        this.title = title;
        this.bound = bound;
    }

    @Override
    public boolean equals(Object obj) {
        if ((obj instanceof Book)) {
            return true;
        }
        return false;
    }
}

CodePudding user response：

The correct implementation would be:

@Override
public boolean equals(Object obj) {
    if(this == obj)
        return true;
    if(!(obj instanceof Book))
        return false;
    Book other = (Book) obj;
    return bound == other.bound && Objects.equals(title, other.title);
}

Both object properties are respected!

** Update **

To avoid using instanceof you should use

if(this.getClass() != obj.getClass())
   return false;

Thanks user16320675 for the hint!

CodePudding user response：

You are almost there. However, the instanceof will always be true here if you are actually comparing to books. The below should work.

class Book {

     private String title;
     private boolean bound;

     public Book(String title, boolean bound) {
         this.title = title;
         this.bound = bound;
     }

     public String getTitle(){
          return this.title;
     }
     public boolean isBound(){
          return this.bound;
     }
     @Override
     public boolean equals(Obj obj) {
          if(!(obj instanceof Book)){
               return false;
          }
          if ((Book) obj.isBound() == this.isBound() && ((Book) obj).getTitle().equals(this.getTitle())) {
               return true;
          }
          return false;
     }
}

Now you can compare two books.

Book b1  = new Book(new String("Title1"), true);
Book b2  = new Book(new String("Title2"), true);
Book b3  = new Book(new String("Title1"), true);

System.out.println(b1.equals(b2)); // Output is false
System.out.println(b1.equals(b3)); // Output is true