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POIs it OK to have an 'empty' class that extends another class?
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copied!<p>Let's say I have one class <code>Foo</code> that has a bunch of logic in it and another class <code>Bar</code> which is essentially the same. However, as <code>Foo</code> and <code>Bar</code> are different (but related) entities I need the difference to be apparent from my code (i.e. I can tell whether an instance is a <code>Foo</code> or a <code>Bar</code>)</p> <p>As I was whacking this together without much thought I ended up with the following:</p> <pre><code>public class Foo { /* constructors, fields, method, logic and what-not */ } public class Bar extends Foo { /* nothing here but constructors */ } </code></pre> <p>Is this OK? Is it better to make <code>Bar</code> a composite class? e.g:</p> <pre><code>public class Bar { private Foo foo; /* constructors and a bunch of wrapper methods that call into foo */ } </code></pre> <p>Or even, while we're at it, something much more low-tech:</p> <pre><code>public class Foo { /* constructors, fields, method, logic and what-not */ private boolean isABar; // Could be an enum } </code></pre> <p>What do you think? <strong>How do you deal with these 'marker classes'?</strong></p> <hr> <p>As an example of how my code may wish to treat <code>Foo</code> and <code>Bar</code> differently, my code would need to be able to do stuff like <code>List<Foo></code> and <code>List<Bar></code>. A <code>Foo</code> couldn't go in a <code>List<Bar></code> and vice versa.</p>

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