Mega Code Archive
This program demonstrates the use of reflection for manipulating arrays
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/*
This program is a part of the companion code for Core Java 8th ed.
(http://horstmann.com/corejava)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.lang.reflect.Array;
/**
* This program demonstrates the use of reflection for manipulating arrays.
*
* @version 1.01 2004-02-21
* @author Cay Horstmann
*/
public class ArrayGrowTest {
public static void main(String[] args) {
int[] a = { 1, 2, 3 };
a = (int[]) goodArrayGrow(a);
arrayPrint(a);
String[] b = { "Tom", "Dick", "Harry" };
b = (String[]) goodArrayGrow(b);
arrayPrint(b);
System.out.println("The following call will generate an exception.");
b = (String[]) badArrayGrow(b);
}
/**
* This method attempts to grow an array by allocating a new array and copying
* all elements.
*
* @param a
* the array to grow
* @return a larger array that contains all elements of a. However, the
* returned array has type Object[], not the same type as a
*/
static Object[] badArrayGrow(Object[] a) {
int newLength = a.length * 11 / 10 + 10;
Object[] newArray = new Object[newLength];
System.arraycopy(a, 0, newArray, 0, a.length);
return newArray;
}
/**
* This method grows an array by allocating a new array of the same type and
* copying all elements.
*
* @param a
* the array to grow. This can be an object array or a primitive type
* array
* @return a larger array that contains all elements of a.
*/
static Object goodArrayGrow(Object a) {
Class cl = a.getClass();
if (!cl.isArray())
return null;
Class componentType = cl.getComponentType();
int length = Array.getLength(a);
int newLength = length * 11 / 10 + 10;
Object newArray = Array.newInstance(componentType, newLength);
System.arraycopy(a, 0, newArray, 0, length);
return newArray;
}
/**
* A convenience method to print all elements in an array
*
* @param a
* the array to print. It can be an object array or a primitive type
* array
*/
static void arrayPrint(Object a) {
Class cl = a.getClass();
if (!cl.isArray())
return;
Class componentType = cl.getComponentType();
int length = Array.getLength(a);
System.out.print(componentType.getName() + "[" + length + "] = { ");
for (int i = 0; i < Array.getLength(a); i++)
System.out.print(Array.get(a, i) + " ");
System.out.println("}");
}
}
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