Java中的子类编译

Question

我已经了解到继承是一种“编译时”现象。在另一个地方，我也了解到超类代码是由类加载器加载的，我推断这是在运行时发生的。这使我对类的本质有些困惑。 sublass的类文件是否包含超类的实际编译代码，还是在运行时进行访问？

Answer 1

So consider you create a class that inherits a class that is included in a 3rd party jar file.

In order to compile your code you need to have the 3rd party jar file in the classpath of your compiler.

In order to run your code you will also need the jar file in the classpath of the java command that launches the application.

Your subclass does not contain the code of the superclass, it is in the jar files. Your compiled class contains a reference to the superclass. When your class is loaded by the classloader it searches the classpath for the superclass and loads it.

Answer 2

Where did you read it's compile time? I guess if you're compiling your subclass then yes, it needs to have a superclass to reference when being compiled.

But when you actually run the code it is dynamically linked as per:

http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-5.html

"The Java Virtual Machine dynamically loads, links and initializes classes and interfaces"