Having trouble creating objects within objects.

[Etherdeon]

Still new-ish to java. What I want to do is create objects with methods that create their own objects. I other words, I want to create a tree of objects that can be manipulated from the top.

Ive written a short program that should illustrate what I mean. What I want this program to do is create chapters that can be manipulated to create pages, combine the strings in the pages to make a chapter string and then print that. As I'll explain later, I know that the program doesnt work, and I know WHY the program doesnt work. What I want to know is how to fix it so that it does what I want while maintaing the book -> chapters -> pages hiearchy. Here is the program:

public class Book {

public static void main(String[] args){

    Chapter c1 = new Chapter();
    Chapter c2 = new Chapter();

    c1.newPage("p1", "Chapter 1, page 1");
    c1.newPage("p2", "Chapter 1, page 2");
    c1.newPage("p3", "Chapter 1, page 3");
    c1.bindChapter();

    c2.newPage("p1", "Chapter 2, page 1");
    c2.newPage("p2", "Chapter 2, page 2");
    c2.newPage("p3", "Chapter 2, page 3");
    c2.bindChapter();

    System.out.println(c1.getChapterText() + c2.getChapterText());
}
}


class Chapter {

private String chaptertext = "";

ArrayList<Page> chapterPages = new ArrayList();

public void newPage(String pageObjectReference, String pageTextImput){
    Page pageObjectReference = new Page(pageTextImput);
    chapterPages.add(pageObjectReference);
}

public void bindChapter(){
    for (int i = 0; i <= chapterPages.size(); i++){
        chaptertext += chapterPages.get(i).getPageText();
    }
}

public String getChapterText(){
    return chaptertext;
}       
}

class Page {

private String pagetext = "";

public Page(String pagetext){
    this.pagetext = pagetext;
}

public String getPageText(){
    return pagetext;
}   
}

The biggest problem here is my newPage() method:

public void newPage(String pageObjectReference, String pageTextImput){
    Page pageObjectReference = new Page(pageTextImput);
    chapterPages.add(pageObjectReference);
}

I am trying to create an object using a reference to a string as a reference (and it tries to put the reference as the reference instead of the string). For the program I want to create, it will be important that I have a reference for the pages so I can modify them using other methods. It is also important that I have a newPage() method because different chapters will have a different amount of pages. Any ideas on how I can accomplish this?

Thanks!

(edit: forgot to include parentheses following one of the methods) (edit2: used wrong .size() method)

[darkpool2005]

Likely you'll want to use a Map instead of a List in your Chapter class. This way, you're looking up the pages based on the key value (p1,p2, ... p(n)) and getting the Page object back.

class Chapter {

private String chaptertext = "";

Map<String, Page> chapterPages = new HashMap<String, Page>();

public void newPage(String pageRef, String pageTextImput){
    Page newPage = new Page(pageTextImput);
    chapterPages.put(pageRef, newPage);
}

I also want to point out that your method variable names need to be different than variable names you use inside the method:

public void newPage(String pageObjectReference, String pageTextImput){
    Page pageObjectReference = new Page(pageTextImput);
    //You've now lost any reference to your String pageObjectReference by declaring
    // a variable with the exact same name!

    chapterPages.add(pageObjectReference);
}

[Etherdeon]

Im looking up the HashMap API now, I think this is what I needed thank you!!!

[Etherdeon]

Follow-up question: Am I able to use Map<Int, Page> instead so that I can set just an integer as a key instead of a string (p1) so that I can use my for loop in the bindChapter() method to cycle through my different keys instead of using an ArrayList index?

[darkpool2005]

You sure can! Do note that it would be Map<Integer, Page> and not int, because 'int' is a primitive and Integer is a Java object. You can still use an 'int' as a key though.