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Java Java Data Structures Exploring the Java Collection Framework ArrayLists

Sean Flanagan
Sean Flanagan
33,235 Points


Let's add a method that returns a list of all links in the body of the document. All words that start with http should be considered links. Name it getExternalLinks.

NOTE: Remember to import the needed classes from java.util. HINT: We already made the getWords method, we should use it!

package com.example;

import java.io.Serializable;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.List;
import java.util.Date;

public class BlogPost implements Comparable<BlogPost>, Serializable {
  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 int compareTo(BlogPost other) {
    if (equals(other)) {
      return 0;
    return mCreationDate.compareTo(other.mCreationDate);

  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;

  private List<String> getExternalLinks() {
    for String word : getWords() {
      if (word.startsWith(http)) {
    return getWords;

1 Answer

Chase Marchione
Chase Marchione
155,055 Points

Hi Sean,

1) The getExternalLinks() method should be public (we want other classes to be able to access this method.)

2) We need to create a new ArrayList of type String.

3) We want to make sure that the condition of our for loop is in parentheses (for the sake of syntax, but it looks nice organization-wise too.)

4) We'll want to put http in double-quotes ("http"), because it is a string of characters.

5) We want the return statement to return our ArrayList (as it contains the list of links that we want to pass back.)

  public List<String> getExternalLinks() {
    List<String> results = new ArrayList<String>();
    for (String word : getWords()) {
      if (word.startsWith("http")) {
    return results;

Hope this helps!

Sean Flanagan
Sean Flanagan
33,235 Points

Hi CJ. Thanks for your input; it was a big help. :-)