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POBetter alternative to downcasting?
 

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  1. POBetter alternative to downcasting?
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    <p>What would be a good alternative pattern to this...?</p> <p><strong>NOTE</strong>: I'm keen to avoid downcasting the objects every time I want to access the sub-class' methods, ie the <code>((Bicycle)vehicles[1]).getSaddles()</code> bit. The sub-classes of <code>Vehicle</code> are only going to be simple with a constructor that takes in values and some getters, but the getters are not the same.</p> <pre><code>public class Main { Vehicle[] vehicles; public static void main(String[] args) { new Main(); } private Main() { DataStuff data = new DataStuff(); vehicles = new Vehicle[data.getNext()]; int i=0; while(i&lt;vehicles.length) { int type = data.getNext(); if (type == 1) { vehicles[i] = new Car(VehicleType.car, data); } else if (type == 2) { vehicles[i] = new Bicycle(VehicleType.bicycle, data); } i++; } if (vehicles[1].type.equals(VehicleType.bicycle)) { System.out.println(vehicles[1].type.toString() + ", number of saddles:" + ((Bicycle)vehicles[1]).getSaddles()); } } public class DataStuff { private int[] data = new int[] {2, 1, 4, 5, 1, 4, 2, 2, 1, 1}; private int pointer = 0; public int getNext() { return data[pointer++]; } } } </code></pre> <p>...</p> <pre><code>public class Vehicle { public VehicleType type; public Vehicle(VehicleType type) { this.type = type; } } </code></pre> <p>...</p> <pre><code>public enum VehicleType { car, bicycle } </code></pre> <p>...</p> <pre><code>public class Bicycle extends Vehicle { private int wheels; private int bells; private int saddles; public Bicycle(VehicleType type, DataStuff data) { super(type); wheels = data.getNext(); bells = data.getNext(); saddles = data.getNext(); } public int getWheels() { return wheels; } public int getBells() { return bells; } public int getSaddles() { return saddles; } } </code></pre> <p>...</p> <pre><code>public class Car extends Vehicle { private int wheels; private int seats; private int engines; private int doors; public Car(VehicleType type, DataStuff data) { super(type); wheels = data.getNext(); seats = data.getNext(); engines = data.getNext(); doors = data.getNext(); } public int getWheels() { return wheels; } public int getSeats() { return seats; } public int getEngines() { return engines; } public int getDoors() { return doors; } } </code></pre> <p><strong>UPDATE 1</strong></p> <p>Assume that the objects ObjectA and ObjectB are completely different(ish) but I must store them in a generic way. ObjectA could be a definition of a country, ObjectB could be a tree...</p> <p><strong>UPDATE 2</strong> </p> <p>(I also updated my psuedo code above to fix an error and make it more obvious) I was hoping not to write too much code as I don't want people getting bogged down with the specifics of my test case, but the code above is close to what I need to achieve.</p> <p>My question was perhaps poorly worded. I'll try to be less vague.</p> <p>So... I have data being read in regarding arbitrary objects in a random order that DO share properties (my code above doesn't reflect this though). I need to be able to iterate through the objects after parsing the int[] and get the specific data for each too... I want to avoid, however, all the downcasting that I would have to do (example in the <code>println</code> statement).</p> <p>What is a good alternative pattern to be using? Or is this going to be ok? I don't have to have huge if else blocks as the data in the int[] (don't worry about the DataStuff class that is just a simple example) will all be generated based on a query (also not shown in the above code) that will be provided by the implementation, so the dev will know what he is expecting back (by developer I mean me anyway lol...).</p> <p>I hope that this is enough info to describe what I'm trying to achieve.</p>
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    1. USNeilos
    1. USNeilos
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    1. COPolymorphism?..
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      1. POBetter alternative to downcasting?
      1. USOliver Charlesworth
    2. COI don't get it, what is it you're trying to do? A baseclass' methods are also available from a subclass.. `new ObjectA(ObjectType.objectA` this looks like a builder, but probably isn't..
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      1. POBetter alternative to downcasting?
      1. USJeroen Vannevel
    3. COIf ObjectA is a country, and ObjectB is a tree, why are they both extending the same base class? *What are you modelling*??
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      1. USAmir Afghani
 

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