Arrays Ext

Our colleague has just finished writing his code and at end of his code, an array is passed to our code. We must carry out some operations on the elements of the array. Since the array could possibly contain various types of objects, we cannot carry out our operations on all the objects. Instead, we’d like pass in a Class object for the type of the object we would like to our on. We would like to create an array from the original array containing only the elements we want.

The heart of code for the arrayExt class is the arExt method. This method takes an object, which is our array, and a Class object, which is the class object of the elements that we want to extract. The first if statement checks if the object we were sent is an array. If it is an array, we get its length so that we can go through the array and check each element. The for loop extracts an element out of the array object and then it checks if the element extracted can be assigned to an object of Class c, which is a parameter of this method. Seeing if it can be assigned to an object of Class c, we are able to extract elements of the type represented by Class c. It is the same type, it is added to a list, which keeps track of all the elements from our array that we are looking for.

arExt method:

public static List arExt(Object arr, Class c){

List ext = new LinkedList();
Class g = arr.getClass();

if(arr.getClass().isArray()) {

int length = Array.getLength(arr);
for(int i=0;i<length;i++) {

Object elm = Array.get(arr,i);

return ext;

} else {

throw new IllegalArgumentException("Invalid Argument");



This example illustrates that we can use Reflection to extract elements of a certain type, which we specified at run-time. Without Reflection, we would be unable to compare the object of the array to a certain type. The use of Reflection has made it much easier to examine the array and add on the objects to a list.

Note: Tutorials at were used to develop this example

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