HashSet

HashSet class

Read the documentation for Class HashSet<E> and answer what methods do the following:

• adds an element a HashSet
• removes an element
• returns the number of elements in a HashSet
• checks whether an element is in a HashSet

HashSet class

• .add(value) adds an element a HashSet
• .remove(value) removes an element
• .contains(value) checks whether an element is in a HashSet
• .size() returns the number of elements in a HashSet

Write Java code

Write an application that reads in a text file with names (one name per line), and prints out each name just once (there are repeated names in the file), in alphabetical order (no need to split the names)

Solution

import java.util.ArrayList;
import java.util.Collections; 
import java.io.File;
import java.io.FileNotFoundException;
import java.util.HashSet;
import java.util.Scanner;


public class UniqueNames {

    public static void main(String[] args)  throws FileNotFoundException {
        File myFile = new File("names.txt");
        Scanner myReader = new Scanner(myFile);
        
        HashSet<String> allNames = new HashSet<String>();
        
        while (myReader.hasNext()) {
            String line = myReader.nextLine();
            allNames.add(line.trim());
        }
        
        myReader.close();
        
        ArrayList<String> sortedNames = new ArrayList<String>(allNames);
        Collections.sort(sortedNames);
        
        for (String name : sortedNames) System.out.println(name);
        

    }

}