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POUpdate subclass given superclass
 

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    <h2>Problem Description</h2> <p>I have an abstract <code>Paper</code> class that contains common properties of all papers and one or more child classes of paper that add additional information for that type of paper. I then have a <code>HashMap&lt;String, Paper&gt;</code> to store multiple papers.</p> <p>My application allows the user to update a paper by providing a the <code>pid</code> and then supplying the attributes and values to update. The issue I am having is how do I update the properties on the sub classes when all I have is the super class.</p> <p><strong>What is the best way/practice to handle this situation?</strong></p> <h2>Class Structure</h2> <pre><code>public abstract class Paper { String pid; String title; String author; } public class Publication extends Paper { int pages; } public class PHDThesis extends Paper { String supervisor; } </code></pre> <hr> <h2>My Current Attempt</h2> <p>This is what I currently have** and it works by using <code>instance of</code>; but I feel there should be a better way to do this.</p> <pre><code>import java.util.*; public class App { public static abstract class Paper { private String title; private String author; public Paper(String title, String author) { this.title = title; this.author = author; } public void update(String title, String author) { this.title = title; this.author = author; } } public static class Publication extends Paper { private int pages; public Publication(int pages, String title, String author) { super(title, author); this.pages = pages; } public void update(String title, String author, int pages) { super.update(title, author); this.pages = pages; } } public static class PHDThesis extends Paper { private String supervisor; public PHDThesis(String supervisor, String title, String author) { super(title, author); this.supervisor = supervisor; } public void update(String title, String author, String supervisor) { super.update(title, author); this.supervisor = supervisor; } } public static void main(String[] args) { HashMap&lt;String, Paper&gt; papers = new HashMap&lt;String, Paper&gt;(); papers.put("P001", new PHDThesis("My Super", "My PHD Title", "My Author")); papers.put("P002", new Publication(22, "My Pub Title", "My Author")); Paper p = papers.get("P001"); if (p instanceof PHDThesis) { ((PHDThesis)p).update("New Title", "New author", "New Super"); } else if (p instanceof Publication) { ((Publication)p).update("New Title", "New author", 33); } } } </code></pre> <p>** reduced test code, actual code is much more complex and better laid out.</p>
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    1. COI have a feeling this has been asked before but I was unable to find an answer. Please link any duplicates if there are any. :)
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    2. CO+1, nicely written question
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