How Does Java Initialize Classes and Interfaces, and What's the Order of Initialization?

Java Order of Initialization and Instantiation

Clarifying Interface Initialization

The order of initialization for interfaces is not explicitly stated in the JLS. However, it is crucial to distinguish between the initialization of a class and the initialization of an object.

Class Initialization

A class or interface is initialized only when it is first accessed, not when an object of that class is created. The initialization process involves:

• Assigning values to compile-time constant fields
• Recursively initializing the superclass (if not already initialized)
• Processing static initializers and static fields (that are not compile-time constants)

Interfaces are initialized when they are first accessed, usually by reading a field that is not a compile-time constant. This access can occur during the evaluation of an initializer, leading to recursive initialization.

Object Initialization

An object is initialized when a new instance is created. The initialization process involves:

• Assigning constructor arguments to parameter variables
• Invoking the superclass constructor (either explicitly or implicitly)
• Running instance initializers and assigning values to instance variables in source code order
• Executing the constructor body

Role of super() Constructor Invocation

An explicit call to the super constructor does not change the order of initialization. It merely specifies which superclass constructor to invoke.

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