OCJP 6

Questions to the Certification Oracle Java 6 Programmer based on the study guide

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Flip-Modus

Class

A template that describes the kinds of state and behavior that objects of its type support

Object

At runtime, when the Java Virtual Machine (JVM) encounters the new keyword, it will use the appropriate class to make an object which is an instance of that class. That object will have its own state, and access to all of

the behaviors defined by its class.

State (instance variables)

Each object (instance of a class) will have its own unique set of instance variables as defined in the class. Collectively, the values assigned to an object's instance variables make up the object's state.

Behavior (methods)

When a programmer creates a class, she creates methods for that class. Methods are where the class' logic is stored. Methods are where the real work gets done. They are where algorithms get executed, and data gets manipulated.

What does it mean to access a class? When we say code from one class (class A) has access to another class (class B), it means class A can do one of three things:

Create an instance of class B.
Extend class B (in other words, become a subclass of class B)
Access certain methods and variables within class B, depending on the access control of those methods and variables

-> in effect, access means visibility.

Access to Class Members:

public

From the same class
from any class in the same package
from a subclass in the same package
from a scubclass outside the same package
from any non-subclass class outside the package

Access to Class Members:

protected

from the same class
from any class in the same package
from a subclass in the same package
from a subclass outside the same package (THROUGH INHERITANCE)

Access to Class Members:

default

from the same class
from any class in the same package
from a subclass in the same package