Even though it doesn't explicitly use the static keyword, the constructor is actually a static method. So the first time an object of type Dog is created, or the first time a static method or static field of class Dog is accessed, the Java interpreter must locate Dog.class, which it does by searching through the classpath.
The constructor is an unusual type of method because it has no return value. This is distinctly different from a void return value, in which the method returns nothing but you still have the option to make it return something else. --原文