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I have a method which converts the Object ( which is an array of primitive or strings) which i have got after invocation of a method (so its in instance of java.lang.Object). I want to build the ArrayList from the input array. I tried using new ArrayList

I have coded something like this 

private List<String> getListOfStringForPrimitives( Object inputObject ) {
     Class<?> inputClass = null;
    if (inputObject != null) {
        inputClass = inputObject.getClass();
    // Returns true if the inputObject is an Array
        if (isTypeAnArray(inputClass.getName())) {
            Class<?> componentType = inputClass.getComponentType();
            // If the inputObject is array of primitives build the list of Strings from the inputObject
            if (isTypePrimitive(componentType.getName())) {
                //ArrayList <String> arryList;
               // build an array list of Strings. from the inputObject and return.
            }
        }
    }
    return arryList;

}

I am stuck how to build the ArrayList from input array! Thanks in advance.

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2 Answers

up vote 1 down vote accepted

Use java.lang.reflect.Array to get the primitive values from the primitive array, and then add the boxed equivalents (e.g. Integer) to the ArrayList.

Write a set of if-then-else clauses that compare componentType to Integer.TYPE, Character.TYPE, etc. In each clause, write the appropriate call to the Array class to get the primitives, and then pass them to Whatever.valueOf, and then stick the results into your Array List.

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We can do that if we know the array is of type int. It can be of int, float, double short or boolean, String(object) in my case. And type I am getting dynamically in the method before hand we don't know that array is of type what. – java_enthu Jun 24 '11 at 16:09
So write a big if/then/else statement. There are only a fixed set of primitive types. You need a different line of code for each. – bmargulies Jun 24 '11 at 16:17
I am not sure if we can do this. Can you show code? and wht about complexity? of putting big if/else? – SmartSolution Jun 24 '11 at 17:14
@bmargulies : do you mean using Array.getInt(inputObject,index)? how shall i get the lengh of the array? I cannot cast inputObject to Object[] and use .length property. – java_enthu Jun 24 '11 at 17:18
@sma this is what the language is like. Yes it will look a bit messy. No I'm not aware of any shortcut. When you get this deep in reflection, you end up with a lot of code. – bmargulies Jun 24 '11 at 17:19
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up vote -1 down vote

Simply use the isArray method: http://www.java2s.com/Code/Java/Reflection/Checkifthegivenobjectisanarrayprimitveornative.htm

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how will it help to build an arrayList of Strings from input array like [1,2,3,4] ? – java_enthu Jun 24 '11 at 16:10
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