COP 3337
SECTION U05
Spring 2017


                      The Use of java.lang.reflect.Array
                      ==================================



I. The Program
--------------


import java.lang.reflect.Array;

public class UsingReflectArray 
{

    public static void main(String[] args) 
    {
        System.out.println("Testing append");
        System.out.println("==============\n\n");
        
        // test 1
        System.out.println("a1 = { 1, 3, 5, 7}");
        System.out.println("a2 = { 2, 4, 6}");
        Integer[] a1 = { 1, 3, 5, 7};
        Integer[] a2 = {2, 4, 6};
        System.out.println("We append a2 at the end of a1.");
        Integer[] a3 = append(a1,a2);
        write("The resulting array", a3);
        
        // test 2
        System.out.println("Another test");
        System.out.println("list1 = { Bill, Mark, Geoff, Peter}");
        System.out.println("list2 = { Christine, Radu, Raju}");
        String[] list1 = { "Bill", "Mark", "Geoff", "Peter"};
        String[] list2 = {"Christine", "Radu", "Raju"};
        System.out.println("We append list2 at the end of list1.");
        String[] list3 = append(list1,list2);
        write("The resulting list", list3);
    }
    
    // return the array obtained by appending  arr2 at the end of arr1
    // if either array is null throw a null pointer exception
    public static <T> T[] append(T[] arr1, T[] arr2)
    {
        if (arr1 == null || arr2 == null)
            throw new NullPointerException("null array(s)");
        // generate the out array
        T[] out = (T[]) Array.newInstance(arr1.getClass().getComponentType(), 
                arr1.length + arr2.length);
        // copy the 2 arrays
        System.arraycopy(arr1,0,out,0,arr1.length);
        System.arraycopy(arr2, 0, out, arr1.length, arr2.length);
        return out;        
    }        
    
    // print an array
    public static <T> void write(String name, T[] arr)
    {
        if (arr == null)
        {
            System.out.println(name + " is null.");
        }    
        else if (arr.length == 0)
        {
            System.out.println(name + " is empty.");
        }    
        else // arr has items
        {
            System.out.println("The contents of " + name + ":");
            for (T item : arr)
                System.out.println(item);
            System.out.println(); // empty line
        }    
    }        
}


II. The Output:
---------------

run:
Testing append
==============


a1 = { 1, 3, 5, 7}
a2 = { 2, 4, 6}
We append a2 at the end of a1.
The contents of The resulting array:
1
3
5
7
2
4
6

Another test
list1 = { Bill, Mark, Geoff, Peter}
list2 = { Christine, Radu, Raju}
We append list2 at the end of list1.
The contents of The resulting list:
Bill
Mark
Geoff
Peter
Christine
Radu
Raju

BUILD SUCCESSFUL (total time: 0 seconds)