2.1 Jb0105: java oop: similarities and differences between java

Revised: Sun Mar 27 11:30:53 CDT 2016

This Page is included in the following Books:

• Programming Fundamentals with Java
• Object-Oriented Programming (OOP) with Java

Table of contents

• Preface
• Similarities and differences
• Miscellaneous

Preface

This module, which presents some of the similarities and differences between Java and C++, is provided solely for the benefit of those students who are already familiar with C++ and are making the transitionfrom C++ into Java.

If you have some familiarity with C++, you may find the material in this module helpful. If not, simply skip this module and move on to the nextmodule in the collection.

In general, students in Prof. Baldwin's Java/OOP courses are not expected to have any specific knowledge of C++.

This module is intended to be general in nature. Therefore, although a few update notes were added prior to publication at cnx.org, no significant effort hasbeen made to keep it up to date relative to any particular version of the Java JDK or any particular version of C++. Changes have occurred in both Java andC++ since the first publication of this document in 1997. Those changes may not be reflected in this module.

Similarities and differences

This list of similarities and differences is based heavily on The Java Language Environment, A White Paper by James Gosling and Henry McGilton and Thinking in Java by Bruce Eckel, which was freely available on the web when this document was first published.

Java does not support typedefs , defines , or a preprocessor . Without a preprocessor, there are no provisions for including header files.

Since Java does not have a preprocessor there is no concept of #define macros or manifest constants . However, the declaration of named constants is supported in Java through use of the final keyword.

Java does not support enums but, as mentioned above, does support named constants . (Note: the enum type was introduced into Java sometime between the first publication of this documentand Java version 7.)

Java supports classes , but does not support structures or unions .

All stand-alone C++ programs require a function named main and can have numerous other functions, including both stand-alone functions and functions that are members of a class. There are no stand-alone functions in Java. Instead, there are only functions that are members of a class, usually called methods.However, a Java application (not a Java applet) does require a class definition containing a main method.

Global functions and global data are not allowed in Java. However, variables that are declared static are shared among all objects instantiated from the class in which the static variables are declared. (Generally, static has a somewhat different meaning in C++ and Java. For example, the concept of a static local variable does not exist in Java as itdoes in C++.)

All classes in Java ultimately inherit from the class named Object . This is significantly different from C++ where it is possible to create inheritance trees that are completely unrelated to one another. All Java objects contain the eleven methods that are inherited from the Object class.