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Java Java Data Structures - Retired Organizing Data Comparable

unable to solve code.where's the error?

The code is perfectly written according to me but I cannot find an error

com/example/BlogPost.java
package com.example;

import java.util.Date;

public class BlogPost implements Comparable {
  private String mAuthor;
  private String mTitle;
  private String mBody;
  private String mCategory;
  private Date mCreationDate;

  public BlogPost(String author, String title, String body, String category, Date creationDate) {
    mAuthor = author;
    mTitle = title;
    mBody = body;
    mCategory = category;
    mCreationDate = creationDate;
  }

  public String[] getWords() {
    return mBody.split("\\s+");
  }

  public String getAuthor() {
    return mAuthor;
  }

  public String getTitle() {
    return mTitle;
  }

  @Override
  public int compareTo(Object obj){
     BlogPost other = (BlogPost)obj;
    if(equals(other)){
      return 0;
    }
    int dateCmp = mCreationDate.compareTo(other.mCreationDate);
    if(dateCmp == 0){
      return mDescription.comareTo(other.mDescription);
    }
    return dateCmp;
  }


  public String getBody() {
    return mBody;
  }

  public String getCategory() {
    return mCategory;
  }

  public Date getCreationDate() {
    return mCreationDate;
  }
}

1 Answer

Hi Mayur,

You're very close! (And you have a typo in your second compareTo() method)

Try this:

  public int compareTo(Object obj){
    BlogPost bp = (BlogPost) obj;
    if(bp.equals(this)){
      return 0;
    }
    if(this.mCreationDate.before(bp.mCreationDate)){
      return -1; 
    }
    return 1;
  }

We cast obj to a BlogPost called bp. If bp is equal to the current instance, this, return zero. Else decide which comes first, using the before method comparing the mCreationDate of both the bp instance and this instance. If they're equal, we return zero and if one is before the other we return 1 or -1 depending on which order they fall in.

I hope that helps.

Steve.

We could use parts of your code to do the same.

If we remove the if statement that looks for equality and compares mDescription - we've done the equals bit already. Then, if we use your other BlogPost instance that you've created you get this:

    public int compareTo(Object obj){
    BlogPost other = (BlogPost) obj;
    if (other.equals(this)){
      return 0;
    }
    int dateCmp = mCreationDate.compareTo(other.mCreationDate); // just return this
    return dateCmp;
    }

That should work. This uses the compareTo() method, rather than the before() method, which is fine. It takes fewer lines of code but adds nothing to the clarity of the output - it isn't user-friendly. You can also return the comparison directly; dateCmp isn't doing anything.

Steve.

Thanks a lot..