public int nextInt() {
return 14;
}
java.lang.Integer.IntegerCache when your JVM starts up. Here’s the code:
import java.lang.reflect.Field;
import java.util.Random;
public class Entropy {
public static void main(String[] args)
throws Exception {
// Extract the IntegerCache through reflection
Class<?> clazz = Class.forName(
"java.lang.Integer$IntegerCache");
Field field = clazz.getDeclaredField("cache");
field.setAccessible(true);
Integer[] cache = (Integer[]) field.get(clazz);
// Rewrite the Integer cache
for (int i = 0; i < cache.length; i++) {
cache[i] = new Integer(
new Random().nextInt(cache.length));
}
// Prove randomness
for (int i = 0; i < 10; i++) {
System.out.println((Integer) i);
}
}
}
92 221 45 48 236 183 39 193 33 84Don’t believe it? Try it on your application! By trying this on your application, you agree to the following licensing terms:
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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That is not enough. You have to start your Java using the command line parameter
java -Djava.lang.Integer.IntegerCache.high=nnnnn
with some very high “nnnnn” number and fill those all with random numbers.
Yes, you’re right. My solution just generates a bit of noise, not enough entropy!
Or you can just change your code to
for (Integer i = 0; i < 10; i++) { System.out.println((Integer) i); }to get more or less than 10 lines ?
Haha, that’s wicked! :-)
Generating random random numbers