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Java Java Data Structures Exploring the Java Collection Framework Sets

Posted by Graham O Connor
Graham O Connor
6,551 Points

Getting lots of errors

./com/example/Blog.java:5: error: expected import.java.util.TreeSet; ^ ./com/example/Blog.java:13: error: illegal start of expression Set set = TreeSet<>(); ^ ./com/example/Blog.java:13: error: -> expected Set set = TreeSet<>(); ^ ./com/example/Blog.java:13: error: ';' expected Set set = TreeSet<>(); ^ ./com/example/Blog.java:15: error: ')' expected for(BlogPost authorName: mPosts){ ^ ./com/example/Blog.java:15: error: not a statement for(BlogPost authorName: mPosts){ ^ ./com/example/Blog.java:15: error: ';' expected for(BlogPost authorName: mPosts){ ^ ./com/example/Blog.java:5: error: package .java.util does not exist import.java.util.TreeSet; ^ ./com/example/Blog.java:11: error: cannot find symbol public set getAllAuthors(){ ^ symbol: class set location: class Blog ./com/example/Blog.java:13: error: cannot find symbol Set set = TreeSet<>(); ^ symbol: variable TreeSet location: class Blog ./com/example/Blog.java:13: error: lambda expression not expected here Set set = TreeSet<>(); ^ ./com/example/Blog.java:17: error: cannot find symbol set.add(authorName.getAuthor()); ^ symbol: variable authorName location: class Blog Note: JavaTester.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. 12 errors

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

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Date;
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 String[] getWords() {
    return mBody.split("\\s+");
  }

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

  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;
  }
}
com/example/Blog.java 
package com.example;

import java.util.List;
import java.util.Set;
import.java.util.TreeSet;


public class Blog {
  List<BlogPost> mPosts;

 public set<String> getAllAuthors(){

  Set<String> set = TreeSet<>();

    for(BlogPost authorName: mPosts){

    set.add(authorName.getAuthor());

    }

  return set;
 }

  public Blog(List<BlogPost> posts) {
    mPosts = posts;
  }

  public List<BlogPost> getPosts() {
    return mPosts;
  }
}
Simon Coates
Simon Coates
28,694 Points
Simon Coates
Simon Coates
28,694 Points

there's an unexpected dot on one of your imports.

the method signature has set<String> instead of Set<String>

treeset instantiation is weird.

1 Answer

Simon Coates
Simon Coates
28,694 Points
Simon Coates
Simon Coates
28,694 Points

the following seems to work:

package com.example;

import java.util.List;
import java.util.TreeSet;
import java.util.Set;

public class Blog {
  List<BlogPost> mPosts;

 public Set<String> getAllAuthors(){

  Set<String> set = new TreeSet<String>();

    for(BlogPost authorName: mPosts){

    set.add(authorName.getAuthor());

    }

  return set;
 }

  public Blog(List<BlogPost> posts) {
    mPosts = posts;
  }

  public List<BlogPost> getPosts() {
    return mPosts;
  }
}