Testing Array of Primitive Vs Array of Object

[Alec Lee]

I have an array whose element type I do not know until runtime. That is, it could be an array to object, array to array, array to primitive. I need a simple method to loop thru the array and test if it contains an element convertible to a certain numeric value. The element include numeric primitives, their wrappers, BigDecimal/BigInteger, any instance of java.lang.Number.

I would use recursion to loop thru the whole array since it may be an array of array. But the problem is how can i test if the array elements are primitive type. Here is my code that failed at line 6 because of casting primitive to Object[]

    
private boolean recurseArray(long testValue, Object array) {
		if (array==null)
			return false;
		if (array.getClass().getName().indexOf("[") == 0) {// is array, loop thru each element and recurse
			for (Object o : (Object[]) array) { // exception some element could be primitive, cannot cast to Object[]
				if (recurseArray(testValue, o))
					return true;
			}
			return false;
		} else {
			if (array instanceof java.lang.Number) { //won't work too, can't use instanceof on primitive
				if (((java.lang.Number) array).longValue() == testValue)
					return true;
			}
			return false;
		}
	}

Exception in thread "main" java.lang.ClassCastException: [I cannot be cast to [Ljava.lang.Object;

[Ernest Friedman-Hill]

The java.lang.Class class has a number of useful methods you're not using. There's isArray() (a vastly better substitute for checking if there's a bracket in the class name!), there's getComponentType() (which tells you the data type of the elements of an array) and there's isPrimitive() which tells you if a class represents a primitive type. So to check if something is a primitive array, you'd do

Object o = ...
if (o.getClass().isArray() && o.getClass().getComponentType().isPrimitive()) {
    // It's a primitive array
}

[Henry Wong]

Alec Lee wrote:But the problem is how can i test if the array elements are primitive type. Here is my code that failed at line 6 because of casting primitive to Object[]

Can you simply test if the array is of the primative type that you want? Instead of testing the elements? ... Or test if the array type is *not* an object array type?

Henry

[Rob Spoor]

Ernest is right. And to get access to the elements you can use java.lang.reflect.Array.