Example Program in Java Using Hashmap,Hashset & Hashtable.
Program also shows adding, deleting elements from these collection types
package HashTable;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
/**
*
* @author Manjeet Kumar
*/
public class HashTableDemo {
public static void main(String[] args) {
//exclusive Demo of hashmap
Map map = new HashMap();
map.put(1, "Abc");
map.put(2, "Def");
map.put(3, "Ijk");
System.out.println("All of the mappings " + map);
//put all mappings of map into map1
Map map1 = new HashMap();
map1.putAll(map);
System.out.println("All of the mappings " + map1);
//Demo of Collections
Hashtable numbers = new Hashtable();
numbers.put("one", new Integer(1));
numbers.put("two", new Integer(2));
numbers.put("three", new Integer(3));
numbers.put("four", new Integer(4));
numbers.put("five", new Integer(5));
numbers.put("Six", new Integer(6));
Integer n = (Integer) numbers.get("two");
if (n != null) {
System.out.println("Two=" + n);
}
HashMap hMap = new HashMap();
hMap.put("A", "apple"); //Without String construtor invocation|
hMap.put("B", new String("ball"));//With String constructor invocation |Both can be used
hMap.put("C", "cat");
hMap.put("D", new String("doll"));
hMap.put("E", "eye");
hMap.put("F", new String("fruit"));
hMap.put("G", "go");
hMap.put("H", new String("Hashmap"));
String s = (String) hMap.get("A");
if (!s.equals(null)) {
System.out.println("A for " + s);
System.out.println("B for " + hMap.get("B"));
}
HashSet hs = new HashSet();
hs.add("Megan");
hs.add("Regan");
hs.add("Donald");
hs.add("Eleen");
hs.add("Cathy");
hs.add("Fiennes");
System.out.println(hs);
//Example using Set
// Create the set
Set set = new HashSet();
// Add elements to the set
set.add("a");
set.add("b");
set.add("c");
System.out.println("SET has following elements(after addition): " + set);
// Remove elements from the set
set.remove("c");
System.out.println("SET has following elements(after Removing C): " + set);
// Get number of elements in set
int size = set.size(); // 2
System.out.println("Number of elements in SET: " + size);
// Adding an element that already exists in the set has no effect
set.add("a");
size = set.size(); // 2
System.out.println("Adding and Element(observe the difference): " + size + " Now SET is " + set + " Because 'a' allready exist in SET");
set.add("m");
size = set.size();
System.out.println("Adding Element other than existing increases size to" + size + "Now SET is: " + set);
// Determining if an element is in the set
boolean a = set.contains("a");
boolean b = set.contains("b"); // true
//b = set.contains("c"); // false
boolean c = set.contains("c");
boolean m = set.contains("m");
System.out.println("Checking if it contains A:" + a);
System.out.println("Checking if it contains B:" + b);
System.out.println("Checking if it contains C:" + c);
System.out.println("Checking if it contains M:" + m);
// Iterating over the elements in the set
Iterator it = set.iterator();
while (it.hasNext()) {
// Get element
Object element = it.next();
System.out.println("Check the Object :" + element);
}
// Create an array containing the elements in the set (in this case a String array)
String[] array = (String[]) set.toArray(new String[set.size()]);
System.out.println("See array: " + array);
}
}
