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    <p>An elegant way of avoiding <code>instanceof</code> without inventing some new artificial method in the base class (with a non-descriptive name such as <code>performAction</code> or <code>doWhatYouAreSupposedToDo</code>) is to <strong>use the <a href="http://en.wikipedia.org/wiki/Visitor_pattern" rel="noreferrer">visitor pattern</a></strong>. Here is an example:</p> <p><strong>Animal</strong></p> <pre><code>import java.util.*; abstract class Animal { String name; public Animal(String name) { this.name = name; } public abstract void accept(AnimalVisitor av); // &lt;-- Open up for visitors. } </code></pre> <p><strong>Lion</strong> and <strong>Deer</strong></p> <pre><code>class Lion extends Animal { public Lion(String name) { super(name); } public void roar() { System.out.println("Roar"); } public void accept(AnimalVisitor av) { av.visit(this); // &lt;-- Accept and call visit. } } class Deer extends Animal { public Deer(String name) { super(name); } public void runAway() { System.out.println("Running..."); } public void accept(AnimalVisitor av) { av.visit(this); // &lt;-- Accept and call visit. } } </code></pre> <p><strong>Visitor</strong></p> <pre><code>interface AnimalVisitor { void visit(Lion l); void visit(Deer d); } class ActionVisitor implements AnimalVisitor { public void visit(Deer d) { d.runAway(); } public void visit(Lion l) { l.roar(); } } </code></pre> <p><strong>TestAnimals</strong></p> <pre><code>public class TestAnimals { public static void main(String[] args) { Animal lion = new Lion("Geo"); Animal deer1 = new Deer("D1"); Animal deer2 = new Deer("D2"); List&lt;Animal&gt; li = new ArrayList&lt;Animal&gt;(); li.add(lion); li.add(deer1); li.add(deer2); for (Animal a : li) a.accept(new ActionVisitor()); // &lt;-- Accept / visit. } } </code></pre>
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    1. POHow to avoid large if-statements and instanceof
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    1. COYes, tend to agree. I can't resist voting up visitor. I love it, but I think you do more than I do. +1
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      1. USAdeel Ansari
    2. COIts regarding the description you added later, with visitor adding any new `Animal` will require modification of `AnimalVisitor`. Whereas, the other option is good to go without this kinda modification. What say you?
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    3. CO@Adeel Ansari, That a good point. It depends on the situation I'd say. It depends on if you want the specific action-implementations to be collected in one class, or if you want them scattered in the different classes. Both are preferable in different situations. In this scenario however, `roar` and `runAway` are so different that I wouldn't want to invent a common name for the two.
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