Clarify exception hierarchy and definitions in introduction

Author: Bahaaio

concepts/exceptions/introduction.md

@@ -8,6 +8,8 @@ An exception is an event that occurs during the execution of a program that disr
 Exceptions are raised explicitly in Java, and the act of raising an exception is called _throwing an exception_.
 The act of handling an exception is called _catching an exception_.
 
+In Java, all exceptions are subclasses of the `Exception` class, which itself is a subclass of `Throwable`.
+
 Java distinguishes two types of exceptions:
 
 1. Checked exceptions
@@ -20,7 +22,7 @@ An example of a checked exception is the `FileNotFoundException` which occurs wh
 
 This type of exception is checked at compile-time: methods that throw checked exceptions should specify this in their method signature, and code calling a method that might throw a checked exception is required to handle it or the code will not compile.
 
-All exceptions in Java that do not inherit from `RuntimeException` are checked exceptions.
+All checked exceptions are subclasses of `Exception` that do not extend `RuntimeException`.
 
 ### Unchecked exceptions
 
@@ -29,7 +31,7 @@ An example of an unchecked exception is the `NullPointerException` which occurs
 
 This type of exception is not checked at compile-time: methods that throw unchecked exceptions are not required to specify this in their method signature, and code calling a method that might throw an unchecked exception is not required to handle it.
 
-All exceptions in Java that inherit from `RuntimeException` are unchecked exceptions.
+All unchecked exceptions inherit from `RuntimeException`, which itself is an extension of `Exception`.
 
 ## Errors