Iterator Pattern
Iterator pattern is the mechanism of accessing all the objects in a collection. To sequentially access the objects of a collection, the iterator pattern defines an interface containing the methods that access the objects of a collection or the aggregate objects without having knowledge about its internal representation. It provides uniform interface to traverse collections of all kinds. Aggregate objects are the objects containing the group of objects as a unit. We can also referred them as container or collection. Hash table and linked list are the examples of aggregate objects.

Example: Lets take an example of employees of a software company and their section, then we add some enumeration capabilities to the Employee class. This class is the collection of employees having their names; employee id and their department and these employees arestored in a Vector.

iNow we simply the enumeration of the Vector itself just to obtain the enumeration of all the employees of the collection. Filtered Enumeration: Suppose we want the employees of the development section. This requires a special enumeration class that access the employees belong only to the development department. The element() method we have defined provides filtered access. Now Enumeration that only returns employees related to the development section is required.

Person.java

import java.util.*;
interface Person {
public abstract double income();
}

Teacher.java

class Teacher implements Person {
private double MonthlyIncome;
private String name;
public Teacher(String name, double i) {
this.name = name;
setMonthlyIncome(i);
}
void setMonthlyIncome(double i) {
if (i > 0) {
MonthlyIncome = i;
} else
MonthlyIncome = 0;
}
public double income() {
return MonthlyIncome;
}
public String getName() {
return name;
}
public String toString() {
return “Teacher: “ + getName();
}}