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POJava Generics and ClassCastException in Generalization
 

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    <p>It might not be related, but this is under Android 2.3.3 and I work with openjdk7.</p> <p>I'm trying to compute the velocity and displacement of an object using its acceleration values, given coordinates in 3 spaces plus time. For that, I created a class named <code>Coord4D</code>, and <code>Velocity</code>, <code>Displacement</code> and <code>Acceleration</code> are child of this class. Like this:</p> <p><code>Coord4D</code>:</p> <pre><code>class Coord4D { // Statics // private static final long ONE_TO_NANO_FACTOR = 1000000000; // Members // private long key; private float xValue; private float yValue; private float zValue; // ... more ... } </code></pre> <p>and an example of inheriting class <code>Velocity</code>:</p> <pre><code>public class Velocity extends Coord4D{ // ... members and methods and stuff ... } </code></pre> <p>And now the problem. In <code>Coord4D</code>, I generalize the method to obtain an antiderivative from derivatives. For instance, I want to retrieve a <code>Velocity</code> instance given two <code>Acceleration</code> instances (past and current) and the <code>Velocity</code> instance from a previous frame.</p> <p>Everything was working fine when the methods to do this were in <code>Displacement</code> and <code>Velocity</code>, but I found it was redundant since both were computing the exact same things, and I hate writing two times the same lines of code. So I decided to move these methods into <code>Coord4D</code>, and to use generics like this:</p> <pre><code>protected static &lt;Derivative extends Coord4D, AntiDerivative extends Coord4D&gt; AntiDerivative getIntegrationStep( Derivative previous, Derivative current, AntiDerivative previousStep){ // Time is in nanoseconds, must change it in seconds float dT = ( current.getTime() - previous.getTime() ) / ONE_TO_NANO_FACTOR; // Parameters have seconds for unit : ..., ?*s, ?, ?/s, ?/s², ... float dX = current.getX() - previous.getX(); float dY = current.getY() - previous.getY(); float dZ = current.getZ() - previous.getZ(); // do the integration step and add the previous step value float x = dX * dT + previousStep.getX(); float y = dY * dT + previousStep.getY(); float z = dZ * dT + previousStep.getZ(); return (AntiDerivative) new Coord4D(current.getTime(), x, y, z); } </code></pre> <p>and the <code>Velocity</code> and <code>Displacement</code> objects have this method (example from <code>Velocity</code>).</p> <pre><code>public static Velocity getVelocity(Acceleration previousAccel, Acceleration currentAccel, Velocity initialVelo) { return getIntegrationStep(previousAccel, currentAccel, initialVelo); } </code></pre> <p>Now, for some reason, this line </p> <pre><code>return getIntegrationStep(previousAccel, currentAccel, initialVelo); </code></pre> <p>result in a <code>ClassCastException</code>. I don't understand why, as I think my logic with the generics is fine. Can someone help me finding where is the flaw?</p> <p>The stack trace (from LogCat):</p> <pre><code>W/dalvikvm(8891): threadid=1: thread exiting with uncaught exception (group=0x4001d648) E/AndroidRuntime(8891): FATAL EXCEPTION: main E/AndroidRuntime(8891): java.lang.ClassCastException: me.aybabt.android.prototypes.physics.Coord4D E/AndroidRuntime(8891): at me.aybabt.android.prototypes.physics.Velocity.getVelocity(Velocity.java:40) E/AndroidRuntime(8891): at me.aybabt.android.prototypes.AcceleratorActivity.onSensorChanged(AcceleratorActivity.java:199) E/AndroidRuntime(8891): at android.hardware.SensorManager$ListenerDelegate$1.handleMessage(SensorManager.java:539) E/AndroidRuntime(8891): at android.os.Handler.dispatchMessage(Handler.java:99) E/AndroidRuntime(8891): at android.os.Looper.loop(Looper.java:150) E/AndroidRuntime(8891): at android.app.ActivityThread.main(ActivityThread.java:4293) E/AndroidRuntime(8891): at java.lang.reflect.Method.invokeNative(Native Method) E/AndroidRuntime(8891): at java.lang.reflect.Method.invoke(Method.java:507) E/AndroidRuntime(8891): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849) E/AndroidRuntime(8891): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607) E/AndroidRuntime(8891): at dalvik.system.NativeStart.main(Native Method) </code></pre>
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    1. COMy guess would be build path issue
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    2. COgenerics tag added
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