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Java Java Data Structures - Retired Exploring the Java Collection Framework ArrayLists

Exploring the Java Collection Framework - Array Lists Challenge

The question is as follows:

"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!"

I feel like I should be close, but I get the following when trying to run the code below:

./com/example/BlogPost.java:38: error: cannot find symbol
    return getWordsPrefixedWith("http");
           ^
  symbol:   method getWordsPrefixedWith(String)
  location: class BlogPost
./com/example/BlogPost.java:45: error: cannot find symbol
      if (word.startsWith(prefix)) {
          ^
  symbol:   variable word
  location: class BlogPost
./com/example/BlogPost.java:46: error: cannot find symbol
        results.add(word);
                    ^
  symbol:   variable word
  location: class BlogPost
Note: JavaTester.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
3 errors

On top of that, I'm still not entirely sure how this all works... (Am I making it more complicated than it really is?)

Any assistance would be greatly appreciated. I've left my "steps" in comments in the code below.

Thanks!

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

import java.io.Serializable;
import java.util.ArrayList;     // Added this...
import java.util.Arrays;       // ...and this...
import java.util.Date;
import java.util.List;        //..and this...

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 List<String> getWords() {          // Changed this from String[] to List<String>...
    String[] words = mBody.split("\\s+");   //Added this using the code that was on the next line...
    return Arrays.asList(words);            // And added this...
  }

  // Added this...
  public List<String> getLinks() {
    return getWordsPrefixedWith("http");
  }

  // Then here's the rest...
  public List<String> getExternalLinks(String prefix) {
   List<String> results = new ArrayList<String>();
    for (String words : getWords()) {
      if (word.startsWith(prefix)) {
        results.add(word);
      }
    }
    return results;
  }

  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;
  }
}

2 Answers

Aha! This got it! :)

package com.example;

import java.io.Serializable;
import java.util.ArrayList;     // Added this...
import java.util.Arrays;        // This...
import java.util.Date;
import java.util.List;        // And this...

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);
  }

  // Changed this, using the example from the video...
  public List<String> getWords() {
    String[] words = mBody.split("\\s+");
    return Arrays.asList(words);
  }

  // Added this...
  public List<String> getExternalLinks() {
   return getWordsPrefixedWith("http"); 
  }

  // And here's the rest...
  public List<String> getWordsPrefixedWith(String prefix) {
    List<String> results = new ArrayList<String>();
    for (String word : getWords()) {
      if (word.startsWith(prefix)) {
       results.add(word); 
      }
    }
    return results;
  }

  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;
  }
}

Though I still don't feel like I fully understand how it works... I kind of feel like I'm staring into an engine, and I can see that this part turns that part but...it's like I'm just zomb-ing out in front of the machine... :\

By the way, is it considered gauche for one to select his or her own answer as the "Best Answer"?

Cory Carlson
Cory Carlson
5,275 Points

import java.util.List; // And this...

Thanks, I didnt have that part imported and was getting the same error.

package com.example;

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

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 List<String> getWords() { String[] words = mBody.split("\s+"); return Arrays.asList(words); } public List<String> getExternalLinks() { List<String> docBody = new ArrayList <String>(); for(String words : getWords()) { if(words.startsWith("http")) { docBody.add(words); } } return docBody; }

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; } }