Question

Describe the main types of collection, their interfaces, and one example class
implementing each type.

Answer 1

Collection type:

1)Set

HashSet,TreeSet

2)List

ArraList,LinkedList

3)Map

HashMap,TreeMap

Collection Interfaces

- Collections are primarily defined through a set of interfaces.

- Supported by a set of classes that implement the interfaces

[Source: java.sun.com]

HashSet example

import com.objectspace.jgl.*;

import java.util.Enumeration;

/**

* Construction, enumeration, rejection of duplicates.

* @see com.objectspace.jgl.HashSet

* @version 3.0.0

* @author ObjectSpace, Inc.

*/

public class HashSet1

{

public static void main(String[] args)

{

HashSet set = new HashSet();

set.add(new Integer(6));

set.add(new Integer(1));

set.add(new Integer(4));

System.out.println(set);

System.out.println();

System.out.println("Enumerate the HashSet");

Enumeration e = set.elements();

while (e.hasMoreElements())

System.out.println(e.nextElement());

System.out.println();

System.out.println("Iterate through the HashSet");

for (HashSetIterator i = set.begin(); !i.atEnd(); i.advance())

System.out.println(i.get());

System.out.println();

System.out.println("Show that duplicates cannot be added.");

}

Object value = set.add(new Integer(8));
if (value != null)
System.out.println("Could not add 8.");
else
{
System.out.println("Added 8");
System.out.println("New contents are " + set);
}
value = set.add(new Integer(4));
if (value != null)
System.out.println("Could not add 4.");
else
{
System.out.println("Added 4.");
System.out.println("New contents are " + set);
}

Arrylist example

import java.util.ArrayList;

public class SimpleArrayListExample {
public static void main(String[] args) {
//create an ArrayList object
ArrayList arrayList = new ArrayList();
//* Add elements to ArrayList using boolean add(Object o) method. It returns true as a general behavior of Collection.add method. The specified object is appended at the end of the ArrayList.
*/
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
/*
Use get method of Java ArrayList class to display elements of ArrayList.
Object get(int index) returns and element at the specified index in the ArrayList
*/
System.out.println("Getting elements of ArrayList");
System.out.println(arrayList.get(0));
System.out.println(arrayList.get(1));
System.out.println(arrayList.get(2));
}
}

HashMap example

import java.util.*;

class HashMapDemo {

public static void main(String args[]) {

// Create a hash map

HashMap hm = new HashMap();

// Put elements to the map

hm.put("John Doe", new Double(3434.34));

hm.put("Tom Smith", new Double(123.22));

hm.put("Jane Baker", new Double(1378.00));

hm.put("Todd Hall", new Double(99.22));

hm.put("Ralph Smith", new Double(-19.08));

// Get a set of the entries
Set set = hm.entrySet();
// Get an iterator
Iterator i = set.iterator();
// Display elements
while (i.hasNext()) {
MapEntry me = (MapEntry)i.next();
System.out.print(me.getKey() + ": ");
System.out.println(me.getValue());
System.out.println();
// Deposit 1000 into John Doe's account
double balance = ((Double)hm.get("John Doe")).doubleValue();
hm.put("John Doe", new Double(balance + 1000));
System.out.println("John Doe's new balance: " + hm.get("John Doe"));
}