Several Useful Items

Collectors This static service class provides terminal operations for streams. Here are a few handy methods.

• Collectors.toCollection(ArrayList::new) will dump your stream into an array list.
• Collectors.toCollection(TreeSet::new) will dump your stream into an a TreeSet, which maintains sortable items in order.
• Collectors.toList() will dump your stream into an a List.
• String has join. Can we "join" items in a stream?

  
  String joined = source.map(e -> e.toString())
                               .joining("|");
  

Flat as a Pancake

You might wonder about these.

• Can I get a stream of words out of a file?
• Can I get a character stream from a file?

You don't get a character stream from a file, you get an IntStream; characters are known by their ASCII value.

import java.nio.file.Files;
import java.nio.file.Path;
import java.io.BufferedReader;
import java.io.IOException;
import java.util.stream.IntStream;

public class ByChars
{
    public static void main(String[] args)
    {
        String fileName = args[0];
        try
        (
            BufferedReader br = Files.newBufferedReader(
                Path.of(fileName));
        )
        {
            IntStream is = br.lines()
                             .map(e -> e + "\n")
                             .flatMapToInt( e -> e.chars());
            is.forEach( e -> System.out.print((char) e));
        }
        catch(IOException ex)
        {
            ex.printStackTrace();
        }
   }
}

Questions

• What do you think flatMapToInt is doing? Do yoiu have a reasonble explanation?
• Dumb question: How can I modify this program to get the sum of the ASCII values of all of the characters in the stream?

import java.io.BufferedReader;
import java.io.IOException;
import java.util.stream.Stream; 
import java.util.Arrays;
import java.nio.file.Files;
import java.nio.file.Path;
public class ByWords
{
    public static void main(String[] args)
    {   
        try 
        {   
            BufferedReader br = Files.newBufferedReader(
                Path.of(args[0]));
            Stream<String> is = br.lines()
                  .flatMap( e -> Arrays.stream(e.split("\\s+")));
            is.forEach(System.out::println); 
        }   
        catch(IOException ex) 
        {   
            ex.printStackTrace();
        }   
    }   
}

public class StreamPuzzles
{
    public static void main(String[] args)
    {
    }
    /**
     * this uses stream operations to filter all
     * duplicates of of a wordlist file and to place it in a
     * List<String>
     */
    public static ArrayList<String> noDuplicates(String fileName)
    {
    }
    //this verson does not use streams
    public static ArrayList<String> noDuplicates1(String fileName)
    {
    }
    /**
     * find the first n words in a file beginning with
     * the character ch and place them in a
     * list of strings.
     */
    public static List<String> findFirstN(String fileName, char ch, int n)
    {
    }
    //no streams version
    public static List<String> findFirstN(String fileName, char ch, int n)
    {
    }
    /**   
     * removes all nonwhitespace, nonalphanumeric characters
     * from the contents of a file and places it in a filen
     * named fileName.out.
     */
    public static vood depunct(String fileName)
    {

    }
    /**
     * Extracts all distinct words used in a file and places
     * them in a file named fileName.voc.  Can you extract
     * the vocabulary from War and Peace (file provided here)?
     */
    public static void vocabulary(String fileName)
    {
    }
}