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However, it is a common practice when extending a Java framework to implement classes in the same package as a framework class to access protected members. The source file may exist in a completely different location, and may be deployed to a different .jar file, yet still be in the same logical path as far as the JVM is concerned. [10]
Classes may inherit from other classes, so they are arranged in a hierarchy that represents "is-a-type-of" relationships. For example, class Employee might inherit from class Person. All the data and methods available to the parent class also appear in the child class with the same names.
The concept of class hierarchy in computer science is very similar to taxonomy, the classifications of species. The relationships are specified in the science of object-oriented design and object interface standards defined by popular use, language designers ( Java , C++ , Smalltalk , Visual Prolog ) and standards committees for software design ...
In class-based programming, inheritance is done by defining new classes as extensions of existing classes: the existing class is the parent class and the new class is the child class. If a child class has only one parent class, this is known as single inheritance , while if a child class can have more than one parent class, this is known as ...
The Java Foundation Classes are comparable to the Microsoft Foundation Class Library (MFC). JFC is an extension of the original Java Abstract Windowing Toolkit (AWT). Using JFC and Swing, an additional set of program components, a programmer can write programs that are independent of the windowing system within a particular operating system.
If a class does not specify its superclass, it implicitly inherits from java.lang.Object class. Thus all classes in Java are subclasses of Object class. If the superclass does not have a constructor without parameters the subclass must specify in its constructors what constructor of the superclass to use. For example:
A Java class file is a file (with the .class filename extension) containing Java bytecode that can be executed on the Java Virtual Machine (JVM).A Java class file is usually produced by a Java compiler from Java programming language source files (.java files) containing Java classes (alternatively, other JVM languages can also be used to create class files).
Instead the class browser allows to edit the class together with its metaclass at the same time. The names of classes in the metaclass hierarchy are easily confused with the concepts of the same name. For instance: Object is the base class that provides common methods for all objects; "an object" is an integer, or a widget, or a Car, etc.