HashSets and hash tables 

• Lists allow for ordered elements, but searching them is very slow.
• Can speed up search tremendously if you dont care about ordering.
• Hash tables let you do this. Drawback is that you have no control over how elements are ordered.
• hashCode() computes integer (quickly) which corresponds to position in hash table.
• Independent of other objects in table.

HashSet  Class 

• Hashing can be used to implement several important data structures.
• Simplest of these is HashSet
  • add elements with add(Object) method
  • contains(Object) is redefined to first look for duplicates.
  • if duplicate exists, Object is not added
• What determines a duplicate?
  • careful here, must redefine both hashCode() and equals(Object)!

HashSet

• Look HashSet Example
• Play around with some additional methods.

/**********************************************************************
 * HashSet in Java Example
 *
 **********************************************************************/

import java.util.*;
public class app {
    public static void main(String[] args) {
        HashSet<String> name = new HashSet<String>();
        name.add("Mark");
        name.add("tom");
        name.add("jack");
        name.add("july");
        name.add("patrik");
        Iterator<String> itr = name.iterator();
        while(itr.hasNext())
            System.out.println(itr.next());
    }
}

/*
Output:
tom
Mark
july
patrik
jack

*/

• Java Simple Programs And Examples
• Java Example – Java Hello World Example
• Java Example – Math and Arithmetic Operators in Java
• Java Example – Variables and Types in Java
• Java Example – Scanner class and Getting User Input using Java
• Java Example – The If-Else If Statement, Nested If Statements, Logical Operators
• Java Example – Arrays in Java Example
• Java Example – ListIterator in Java Example
• Java Example – How to get current timestamp using Java
• Java Example – HashSet in Java with Example
• Java Example – How to read file in Java using BufferedReader
• Java Example – How to get Current Directory in Linux/Windows
• Java Example – Program to reverse an array or string
• Java Example – Sort String Array
• Java Example – Comparing two strings
• Java Example – String concatenation (join strings)
• Java Example – Java String Contains example

• Java Conversion
• Java Example – Convert String to int
• Java Example – Convert Date to String
• Java Example – Convert String to Character Array
• Java Example – Convert into string
• Java Example – Convert ArrayList to String Array
• Java Example – Convert Char Array To String
• Java Example – String Array To List

• Java Sorting algorithms & Techniques
• Java Example – Bubble Sort Algorithm
• Java Example – Insertion Sort Algorithm
• Java Example – Selection Sort Algorithm
• Java Example – Quick Sort Algorithm
• Java Example – Merge Sort Algorithm

• Java Handling Files
• Java I/O – Check If File Path Absolute or not
• Java I/O – Get file name and file path
• Java I/O – Get parent directory of the file or directory
• Java I/O – How to write to a file using BufferedWriter
• Java I/O – How to write to a file using FileOutputStream
• Java I/O – Check file permission and Set file permission
• Java I/O –  Read File Using Java BufferedInputStream
• Java I/O – How to create a file in Java