How to cast an java Object to its own getComponentType?

Question

I've a Class containing a private list of objects.

private List<Object> mylist;

Additionally my class contains two methods:

(1) addObject

public void addObject(Object obj)

{

    this.mylist.add(obj);

}

(2) dropObject

dropObject is a bit tricky. I want do drop the first element from

mylist

that is equal (but not the same) to the parameter

obj

. Therefore I compare the class of the parameter

obj

to every element's class in

mylist

. If the class of the current element matches, I want to compare, whether both elements are equal (but not the same).

Here I've got some problem to compare arrays with each other. I'd like to use

Array.deepEquals()

which requires a typecast for both

obj

and

curr_obj

.

So here's my code:

public void dropArgument(Object obj) {



    if (obj == null) {

        return;

    }



    Object objRemove = null;



    for (Object curr_obj : this.mylist) {



        if (curr_obj.getClass() != obj.getClass()) {

            continue;

        }



        // primitive data type comparison

        if (obj.getClass().isPrimitive() && curr_obj == obj) {

            objRemove = curr_obj;

        } 

        // array comparison

        else if ((obj.getClass().isArray())

                /* the following line gives me headache */

                && (Arrays.deepEquals((Object[]) curr_obj, (Object[]) obj))) {

            objRemove = curr_obj;

        }

        // wrapper / collection comparison

        else if (curr_obj.equals(obj)) {

            objRemove = curr_obj;

        }

        // comparison of any other classes which are assumed not to have an 'equals' method.

        else {

            Field[] fInputFields = obj.getClass().getDeclaredFields();

            Field[] fFields = curr_obj.getClass().getDeclaredFields();

            if (Arrays.deepEquals(fInputFields, fFields)) {

                objRemove = curr_obj;

            }

        }

    }



    // delete obj match if found

    if (objRemove != null) {

        this.mylist.remove(objRemove);

    }

}

I wrote tests for this method and every type of array get's the following (stackstrace of an int[] array):

error:

java.lang.ClassCastException: [I cannot be cast to [Ljava.lang.Object;

    at javafxTablePane.FieldMethodData.dropArgument(FieldMethodData.java:119)

    at tests.DropArgumentsTests.test_dropMultiArrayInteger(DropArgumentsTests.java:345)

    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

    at java.lang.reflect.Method.invoke(Method.java:498)

    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)

    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)

    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)

    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)

    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)

    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)

    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)

    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)

    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)

    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)

    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)

    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)

    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)

    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)

    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)

    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)

    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)

    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)

    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

The error is clear:

int[]

can't be typecasted to

Object[]

. So my question is, as

Array.deepEquals()

requires a typecast, how can I re-cast my objects to their own class/data type as array?

I searched for this and found the

getClass().getComponentType()

method with delivers the array type of my object. But I don't know (if even possible) how to use that to typecast

obj

to its own array-type.

Some additional infos:

I want to use
Object obj
as parameter for my method to be able to get any object independent of class or data type.

I am aware, that I could simply overload my method to handle each data type itself. But I try to solve this generic.

Update

I've followed Darshan Mehta's suggestion and implemented a simple method that converts 1 dimensional arrays from primitive to wrapper classes. I can continue developing more generic code (e.g. casting arrays of any dimension) with that, so this solution fits my issue. I have put my code here for those who are interested.

/**

 * <b>ArrayEquals</b>

 * <p>

 * Compares two arrays of any same class and delivers their equality as boolean.

 * </p>

 * 

 * @param obj1

 *            [Object] : any object of any class as Object

 * @param obj2

 *            [Object] : any object of the same class as obj1 as Object

 * @return [boolean] : Equality of obj1 and obj2

 */

private boolean ArrayEquals(Object obj1, Object obj2) {



    Class<?> cObj1 = obj1.getClass().getComponentType();



    // convert byte[] to Byte[]

    if (cObj1.equals(byte.class)) {



        byte[] tmpObj1 = (byte[]) obj1;

        byte[] tmpObj2 = (byte[]) obj2;

        if (tmpObj1.length != tmpObj2.length) {

            return false;

        }

        Byte[] newObj1 = new Byte[tmpObj1.length];

        Byte[] newObj2 = new Byte[tmpObj2.length];



        for (int i = 0; i < tmpObj1.length; i++) {

            newObj1[i] = tmpObj1[i]; // Autoboxing

            newObj2[i] = tmpObj2[i]; // Autoboxing

        }

        return Arrays.deepEquals(newObj1, newObj2);

    }

    // convert short[] to Short[]

    else if (cObj1.equals(short.class)) {

        short[] tmpObj1 = (short[]) obj1;

        short[] tmpObj2 = (short[]) obj2;

        if (tmpObj1.length != tmpObj2.length) {

            return false;

        }

        Short[] newObj1 = new Short[tmpObj1.length];

        Short[] newObj2 = new Short[tmpObj2.length];



        for (int i = 0; i < tmpObj1.length; i++) {

            newObj1[i] = tmpObj1[i]; // Autoboxing

            newObj2[i] = tmpObj2[i]; // Autoboxing

        }



        return Arrays.deepEquals(newObj1, newObj2);

    }

    // convert int[] to Integer[]

    else if (cObj1.equals(int.class)) {

        Integer[] newObj1 = Arrays.stream((int[]) obj1).boxed().toArray(Integer[]::new);

        Integer[] newObj2 = Arrays.stream((int[]) obj2).boxed().toArray(Integer[]::new);

        return Arrays.deepEquals(newObj1, newObj2);

    }

    // convert long[] to Long[]

    else if (cObj1.equals(long.class)) {

        Long[] newObj1 = Arrays.stream((long[]) obj1).boxed().toArray(Long[]::new);

        Long[] newObj2 = Arrays.stream((long[]) obj2).boxed().toArray(Long[]::new);

        return Arrays.deepEquals(newObj1, newObj2);

    }

    // convert float[] to Float[]

    else if (cObj1.equals(float.class)) {

        float[] tmpObj1 = (float[]) obj1;

        float[] tmpObj2 = (float[]) obj2;

        if (tmpObj1.length != tmpObj2.length) {

            return false;

        }

        Float[] newObj1 = new Float[tmpObj1.length];

        Float[] newObj2 = new Float[tmpObj2.length];



        for (int i = 0; i < tmpObj1.length; i++) {

            newObj1[i] = tmpObj1[i]; // Autoboxing

            newObj2[i] = tmpObj2[i]; // Autoboxing

        }



        return Arrays.deepEquals(newObj1, newObj2);

    }

    // convert double[] to Double[]

    else if (cObj1.equals(double.class)) {

        double[] tmpObj1 = (double[]) obj1;

        double[] tmpObj2 = (double[]) obj2;

        if (tmpObj1.length != tmpObj2.length) {

            return false;

        }

        Double[] newObj1 = new Double[tmpObj1.length];

        Double[] newObj2 = new Double[tmpObj2.length];



        for (int i = 0; i < tmpObj1.length; i++) {

            newObj1[i] = tmpObj1[i]; // Autoboxing

            newObj2[i] = tmpObj2[i]; // Autoboxing

        }



        return Arrays.deepEquals(newObj1, newObj2);

    }

    // convert boolean[] to Boolean[]

    else if (cObj1.equals(boolean.class)) {

        boolean[] tmpObj1 = (boolean[]) obj1;

        boolean[] tmpObj2 = (boolean[]) obj2;

        if (tmpObj1.length != tmpObj2.length) {

            return false;

        }

        Boolean[] newObj1 = new Boolean[tmpObj1.length];

        Boolean[] newObj2 = new Boolean[tmpObj2.length];



        for (int i = 0; i < tmpObj1.length; i++) {

            newObj1[i] = tmpObj1[i]; // Autoboxing

            newObj2[i] = tmpObj2[i]; // Autoboxing

        }



        return Arrays.deepEquals(newObj1, newObj2);

    }

    // convert char[] to Character[]

    else if (cObj1.equals(char.class)) {

        char[] tmpObj1 = (char[]) obj1;

        char[] tmpObj2 = (char[]) obj2;

        if (tmpObj1.length != tmpObj2.length) {

            return false;

        }

        Character[] newObj1 = new Character[tmpObj1.length];

        Character[] newObj2 = new Character[tmpObj2.length];



        for (int i = 0; i < tmpObj1.length; i++) {

            newObj1[i] = tmpObj1[i]; // Autoboxing

            newObj2[i] = tmpObj2[i]; // Autoboxing

        }

        return Arrays.deepEquals(newObj1, newObj2);

    }

    // is no primitive

    else {

        return Arrays.deepEquals((Object[]) obj1, (Object[]) obj2);

    }

}

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Answer 1

As you are comparing two objects, you should do the following:

Extract out the comparison logic into a new method (e.g. private boolean equals(Object o1, Object o2) and call it from your dropObject method).
For Array type, get component type using array.getClass().getComponentType() method call and try to cast it in an appropriate array. Casting an int array to Object array will throw ClassCastException. Refer to this SO answer for more explanation on casting and array type.
If a component type is an array, implement the logic to iterate over all the elements and call equals method for each element.

How to cast an java Object to its own getComponentType?

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