Design Pattern: Iterator Pattern in Java

Iterator pattern is used to traverse and iterate through a list of items.

Check Details of Iterator Pattern

This article demonstrates Iterator pattern implementations in Java. Check the following examples.

Examples

Check the following examples of the Iterator pattern implementation in Java-

Example #1: Pagination Iterator

Let’s take the example of storing and showing pagination items.

Page Item Class [General Class]

// Page.java

package com.bigboxcode.designpattern.iterator.pagination;

public class Page {
    private int number;
    private String path;


    public int getNumber() {
        return number;
    }

    public void setNumber(int number) {
        this.number = number;
    }

    public String getPath() {
        if (path == null) {
            return "/page/" + number;
        }

        return path;
    }

    public void setPath(String path) {
        this.path = path;
    }
}

Page List Interface

// AbstractPageList.java

package com.bigboxcode.designpattern.iterator.pagination;

public interface AbstractPageList {
    void add(Page page);
    void remove(Page page);

    AbstractIterator iterator();
}

Page List Class

// PageList.java

package com.bigboxcode.designpattern.iterator.pagination;

import java.util.ArrayList;
import java.util.List;

public class PageList implements AbstractPageList {
    private List<Page> pages = new ArrayList<>();
    @Override
    public void add(Page page) {
        pages.add(page);
    }

    @Override
    public void remove(Page page) {
        pages.remove(page);
    }

    @Override
    public AbstractIterator iterator() {
        return new Iterator(pages);
    }
}

Iterator Interface

// AbstractIterator.java

package com.bigboxcode.designpattern.iterator.pagination;

public interface AbstractIterator {

    boolean hasNext();

    Page next();
}

Iterator Class

//Iterator.java

package com.bigboxcode.designpattern.iterator.pagination;

import java.util.List;

public class Iterator implements AbstractIterator {
    private int currentPosition = 0;
    private final List<Page> pages;

    public Iterator(List<Page> pages) {
        this.pages = pages;
    }
    @Override
    public boolean hasNext() {
        return currentPosition < pages.size();
    }

    @Override
    public Page next() {
        Page page = pages.get(currentPosition);
        currentPosition++;

        return page;
    }
}

Demo

// Demo.java

package com.bigboxcode.designpattern.iterator.pagination;

public class Demo {
    public static void main(String[] args) {
        PageList pageList = populatePageList();
        AbstractIterator paginator = pageList.iterator();

        while(paginator.hasNext()) {
            Page page = paginator.next();

            System.out.println("Page Number: " + page.getNumber());
            System.out.println("Page Path: " + page.getPath());

            System.out.println("----------------------------------------");
        }
    }

    // Dummy function to populate the pagination list
    private static PageList populatePageList() {
        PageList pageList = new PageList();

        for (int i = 0; i < 10; i++) {
            Page page = new Page();
            page.setNumber(i);

            pageList.add(page);
        }

        return pageList;
    }
}

Output

Page Number: 0
Page Path: /page/0
----------------------------------------
Page Number: 1
Page Path: /page/1
----------------------------------------
Page Number: 2
Page Path: /page/2
----------------------------------------
Page Number: 3
Page Path: /page/3
----------------------------------------
Page Number: 4
Page Path: /page/4
----------------------------------------
Page Number: 5
Page Path: /page/5
----------------------------------------
Page Number: 6
Page Path: /page/6
----------------------------------------
Page Number: 7
Page Path: /page/7
----------------------------------------
Page Number: 8
Page Path: /page/8
----------------------------------------
Page Number: 9
Page Path: /page/9
----------------------------------------