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POseek better design to have multi-dispatching with java
 

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  1. POseek better design to have multi-dispatching with java
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    <p>In a language not supporting multiple dispatching, such as Java, the code would probably look something like this </p> <pre><code>/* Example using run time type comparison via Java's "instanceof" operator */ interface Collideable { void collideWith(Collideable other); } class Asteroid implements Collideable { public void collideWith(Collideable other) { if (other instanceof Asteroid) { System.out.println("AAAAAA"); } else if (other instanceof Spaceship) { System.out.println("BBBBBB"); } else if (other instanceof Plane) { System.out.println("CCCCCCC"); } } } class Spaceship implements Collideable { public void collideWith(Collideable other) { if (other instanceof Asteroid) { System.out.println("DDDDDDD"); } else if (other instanceof Spaceship) { System.out.println("EEEEEEE"); } else if (other instanceof Plane) { System.out.println("FFFFFFF"); } } } class Plane implements Collideable { public void collideWith(Collideable other) { if (other instanceof Asteroid) { System.out.println("GGGGGGG"); }else if (other instanceof Spaceship) { System.out.println("HHHHHHH"); }else if (other instanceof Plane) { System.out.println("KKKKKK"); } } } </code></pre> <p>As the visitor pattern can help to solve this problem, I'm thinking if I should impl each leaf class with void collideWith() { visitor.visit(this); // visitor is set in the setter }</p> <pre><code>interface Visitor { void visit(Collideable c); void visit(Asteroid c); void visit(Spaceship c); void visit(Plane c); } </code></pre> <p>Then each unique println should be implemented in subclass of visitor as below? </p> <pre><code>class AsteroidVisitor implements Visitor { void visit(Collideable c) {} void visit(Asteroid c) { System.out.println("AAAAAA"); } void visit(Spaceship c) { System.out.println("BBBBBBB"); } void visit(Plane c) { System.out.println("CCCCCC"); } } //etc for SpaceshipVisitor and PlaneVisitor() </code></pre> <p>Is it the best way to deal with this kind of refactoring to replace instanceof?</p> <p>EDIT: The print out is just example of unique operations in each method, not the ultimate result. I modify my example to be clear.</p>
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    1. COPlease format the code properly!
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    2. COhttp://codereview.stackexchange.com/
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    3. COyour modified example shows your "ultimate result"? I dont think so. please explain the rule, why is it AAA ( BBB CCC DDD EEE )?
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