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Java Java Data Structures Organizing Data Comparable

Facing problem in compareTo implementation

I am getting error in my program that it is not able to identify private variables of the argument object in the compareTo implementation method. Can someone help please.

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;

  public String getBody() {
    return mBody;

  public String getCategory() {
    return mCategory;

  public Date getCreationDate() {
    return mCreationDate;

  public int compareTo(Object obj)
     obj = (BlogPost) obj;
     if (equals(obj))
        return 0;
    int cmp = this.mCreationDate.compareTo(obj.mCreationDate); 
     if ( cmp == 0)
         return (this.mTitle.compareTo(obj.mTitle)); 
     return (this.mCreationDate.compareTo(obj.mCreationDate));


1 Answer

Here you go:

  public int compareTo(Object o) {
    BlogPost other = (BlogPost) o;   //cast o to BlogPost
    if (this == other) {  //check for equality
      return 0;
    } else if (this.getCreationDate().before(other.getCreationDate())) {  //compare Dates, using before() method
      return -1;
    } else {
      return 1;