Design Pattern Study Notes 1 - Iterator

Problem:

A team has one or multiple members, now print the member information one by one.

Solution:

iterator pattern.

1) define an iterator interface.

====================== MyIterator.java ==================

package test.pattern.iterator;

/**

 *  This is the customized iterator interface.

 *

 */

public interface MyIterator {

public boolean hasNext();

public Object next();

}

2) define aggregate interface

====================== Aggregate.java ==================

package test.pattern.iterator;

public interface Aggregate {
MyIterator iterator();
}

3) member class to encapsulate member's information

====================== Member.java =====================

package test.pattern.iterator;

public class Member {

private String name;

private int age;

        // getter and setter methods

}

4) team class to implement Aggregate class

==================== Team.java =======================

package test.pattern.iterator;

public class Team implements Aggregate {

private Member[] members;

private int last;

public Team(int maxSize) {

members = new Member[maxSize];

this.last = 0;

}

public void addMember(Member member){

this.members[last]=member;

last++;

}

public int getLength() {

return members.length;

}

public Member getMemberAt(int index) {

return members[index];

}

public MyIterator iterator() {

return new TeamIterator(this);

}

}

5) TeamIterator class to implement MyIterator interface

=================== TeamIterator.java ================

package test.pattern.iterator;

public class TeamIterator implements MyIterator {

private Team team;

private int index;

public TeamIterator(Team team) {

this.team = team;

this.index = 0;

}

public boolean hasNext() {

if (index >= 0 && index < team.getLength())

return true;

return false;

}

public Object next() {

Member member = team.getMemberAt(index);

index++;

return member;

}

}

6) test class

==================== Client.java ===================

package test.pattern.iterator;

public class Client {

public static void main(String[] args) {

Team team = new Team(5);

team.addMember(new Member("member A", 10));

team.addMember(new Member("member B", 11));

team.addMember(new Member("member C", 12));

team.addMember(new Member("member D", 13));

team.addMember(new Member("member E", 15));

MyIterator it = team.iterator();

while (it.hasNext()) {

Member mem = (Member) it.next();

System.out.println(mem.getName() + "'s age is " + mem.getAge());

}

}

}

This is the output:

member A's age is 10

member B's age is 11

member C's age is 12

member D's age is 13

member E's age is 15

------------

After jdk1.5,  for-loop is another solution.