Reflection - Beginning Java 8 Language Features - page 99

Listing 3-15. Checking for Reflect Permission in a Program

// ReflectPermissionTest.java
package com.jdojo.reflection;

import java.lang.reflect.ReflectPermission;

public class ReflectPermissionTest {
public static void main(String[] args) {
try {
// Create a permission object
ReflectPermission rp = new ReflectPermission("suppressAccessChecks");

// check for permission
rp.checkGuard(null);
System.out.println("Reflect permission is granted");
}
catch (SecurityException e) {
System.out.println("Reflect permission is not granted");
}
}
}

Reflecting on Arrays
Java provides special APIs to work with arrays. The Class class lets you find out if a Class reference represents an
array by using its isArray() method. You can also create an array, and read and modify its element's values using
reflection. The java.lang.reflect.Array class is used to dynamically create an array and to manipulate its elements.
As stated before, you cannot reflect on the length field of an array using normal reflection procedure. However, the
Array class provides you the getLength() method to get the length value of an array. Note that all methods in the
Array class are static and most of them have the first argument as the array object's reference on which they operate.
To create an array, use the newInstance() static method of the Array class. The method is overloaded and it has
two versions.

Object newInstance(Class<?> componentType, int arrayLength)

•

Object newInstance(Class<?> componentType, int... dimensions) •

One version of the method creates an array of the specified component type and the array length. The
other version creates an array of the specified component type and dimensions. Note that the return type of the
newInstance() method is Object . You will need to use an appropriate cast to assign it to the actual array type.
If you want to create an array of int of length 5, you would write

int[] ids = (int[])Array.newInstance(int.class, 5);

The above statement is the same as

Object ids = new int[5];

If you want to create an array of int of dimension 5 X 8 , you would write

int[][] matrix = (int[][])Array.newInstance(int.class, 5, 8);