Enumeration in Java
Enumeration is a legacy interface in Java. It is using to iterate elements in legacy collections like Hashtable .This discussion gives a basic overview on enumeration in Java
Enumeraton Vs Iterator
Both are interfaces in Java for iterating data in a collections .Iterator is the improved version of Enumeration.The method names are shorter in case of Iterator.And one remove() method has been added in Iterator interface.
Methods in Enumeration
1)boolean hasMoreElements()
2)E nextElement()
Methods in Iterator
1) boolean hasNext()
2) E next()
3) void remove()
Iterating Vector using Enumeration
Let us see how the legacy class Vector is iterating using Enumeration.In our example we are storing a number of Strings in our Vector.Then iterating them using an Enumeration object.
import java.util.Enumeration;
import java.util.Vector;
public class EnumerationSample {
private Vector vector = null;
private Enumeration enumeration = null;
public EnumerationSample() {
vector = new Vector();
}
public void addItems() {
vector.add("cat");
vector.add("cow");
vector.add("sheep");
vector.add("dog");
System.out.println("Added items to vector");
}
public void showItems() {
System.out.println("Now iterating using Enumeration..");
enumeration = vector.elements();
while (enumeration.hasMoreElements()) {
System.out.println(enumeration.nextElement());
}
}
public static void main(String[] args) {
EnumerationSample sample = new EnumerationSample();
sample.addItems();
sample.showItems();
}
}
Let us verify the output
Output
Added items to vector
Now iterating using Enumeration..
cat
cow
sheep
dog
Iterating Hashtable using Enumeration
Now let us see how a Hashtable is iterating using Enumeration. Here ,we are using Integer objects as keys and String as values.After inserting data as key – value pair, an Enumeration object is using to get the key values. Then displaying the value mapped with each key.
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
public class HashTableE {
private Map<Integer, String> map = null;
private Enumeration enumeration = null;
public HashTableE() {
map = new Hashtable<Integer, String>();
}
public void addItems() {
map.put(0, "cat");
map.put(1, "cow");
map.put(2, "sheep");
map.put(3, "dog");
System.out.println("Added key value pairs");
}
public void displayItems() {
enumeration = ((Hashtable) map).keys();
System.out.println("Keys in Enumeration are : ");
while (enumeration.hasMoreElements()) {
Integer number = (Integer) enumeration.nextElement();
System.out.println("Key = " + number);
System.out.println("value = " + map.get(number));
}
}
public static void main(String[] args) {
HashTableE sample = new HashTableE();
sample.addItems();
sample.displayItems();
}
}
Let us see the output.
Output
Added key value pairs
Keys in Enumeration are :
Key = 3
value = dog
Key = 2
value = sheep
Key = 1
value = cow
Key = 0
value = cat
The two examples discussed above gives a clear idea about Enumeration interface.