CODEWITHSUNDEEP
javainheritancecompile-time
Mangesh Kherdekar
Mangesh Kherdekar

Reputation: 313

Subclass compilation in Java

I have read that Inheritance is a "compile-time' phenomenon. Also in a different place I have read that the superclass code is loaded by classloader, which I deduce happens at run-time. This is causing me some confusion regarding the nature of inheritance. Does the class file of sublass contain the actual compiled code of superclass, or is it accessed at run-time?

Upvotes: 5

Views: 1845

Answers (2)

rainkinz
rainkinz

Reputation: 10394

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"

Upvotes: 1

mikea
mikea

Reputation: 6667

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.

Upvotes: 4

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