ADDITIONAL SYSTEM INFORMATION :
Ubuntu (16.04.4 LTS) 64-bit OS.

A DESCRIPTION OF THE PROBLEM :
Please go through the source code that I have shared. The source code has sufficient code as part of the comment, where I have explained the details. I might be incorrect in my understanding, nonetheless, it can be verified by appropriate professionals at Oracle.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Please go through the source code that I have shared in the field - 'Source code for an executable test case' on this web-page.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
A runtime exception when the code is executed, per my understanding.
ACTUAL -
The program outputs successfully without any runtime exception as follows:
java.lang.RuntimeException
java.lang.IllegalArgumentException
java.lang.NullPointerException
java.lang.NumberFormatException

---------- BEGIN SOURCE ----------
package bugs.generics;

import java.util.ArrayList;
import java.util.List;

/**
 *
 * @author sawanpatwari
 *
 */
public class UpperBoundWildCardBug {

public static void main(String[] args) {
// TODO Auto-generated method stub
List<RuntimeException> list = new ArrayList<>();
list.add(new RuntimeException());
list.add(new IllegalArgumentException());
list.add(new NullPointerException());
list.add(new NumberFormatException());

printExtendsExceptions(list);

/*
The above function call with the parameter 'list' of type 'List<RuntimeException>'
doesn't adhere to one of the rules of Java, which is, a class cannot extend itself.
example:

class Parent extend Parent{// this gives compile time error.

}

*/


/*
The output of the method call doesn't throw any runtime exception instead
it executes properly. This means that the statement -
'RuntimeException class extends itself' is true.

//technically, below sort of class is valid.
class RuntimeException extends RuntimeException{

}

*/
}

/*The wild card - '?' shouldn't accept an instance of the class -
'RuntimeException' as part of the input parameter -
'list' since the class 'RuntimeException' doesn't extend itself.

Expected Output: A runtime exception being thrown when the program is executed.
*/
public static void printExtendsExceptions(List<? extends RuntimeException> list) {
for (RuntimeException x : list)
System.out.println(x);
}

}

---------- END SOURCE ----------