Head first Java is worth looking at in Java or on the object-oriented novice.

After reading this book I learned a lot.

The content is very friendly to Java and the object-oriented beginner.

Abstract content used in graphical methods to analyze, easy to understand

Before looking at the C # Primer Classic object-oriented, still thick confused.

(1) Very puzzled why the instantiation should be written as a = new A ();

Puzzled why "A should repeat two times";

Wondering why "There is a on both sides of the equals sign, it feels like saying ' a=a ' such nonsense";

(2) Do not know what is polymorphism, why is object-oriented features, what benefits and so on.

(3) A class that is not known to be abstracted (abstract), and what exactly is a decorated class.

Later, it became clear that abstract classes are classes that cannot be instantiated.

Why can't I instantiate it? Because it cannot or should not be instantiated. For example: Animal This class, you can instantiate its subclasses such as dog, Cat, mouse these specific classes, specific animals. But there is no animal called animal--animal, the animal is an abstract concept and should be an abstract class. cannot be instantiated. (What we usually see are cats, dogs, rabbits, animals, not animals.) ）

Head first Java is worth looking at in Java or on the object-oriented novice.