Data Types – Reference Types Objective • To understand what reference types are • The need to study reference types • To understand Java standard packages • To differentiate between Java defined types and user defined types • To have a deeper understanding of the String class • To get acquainted with the Math class • To get acquainted with the Wrapper classes
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Data Types – Reference Typessmithjo/classnotes_2xxxx/powerPoints/lesson...Data Types – Reference Types • Reference types - any data type that is composed of primitive data types
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Data Types – Reference Types
Objective
• To understand what reference types are
• The need to study reference types
• To understand Java standard packages
• To differentiate between Java defined types and user defined types
• To have a deeper understanding of the String class
• To get acquainted with the Math class
• To get acquainted with the Wrapper classes
Data Types – Reference Types
• Reference types - any data type that is composed of primitive data types as its
based type.
• In other words, it is an aggregate of primitive types.
• Reference types in Java are:
The array data structure, and
The class data type.
• In this section we will briefly discuss the concept of array.
• We will discuss the class type to the extent of the fundamental classes of Java.
Reference Types - Array
• Array
• An array is a set of storage locations set aside to hold one type of data.
• It is simply a means where by we can store values of the same type by using
one generic name.
• The list of items are stored linearly
• Hence the items can be accessed by their relative position in the list.
• Arrays are real objects in Java.
• Storage space is allocated for an array during execution time.
• The concept will be discussed fully in future lesson
Reference Types - Array
10 20 30 40 50 60 70 80
arr
indeces
0 1 2 3 4 5 6 7
Data
This is the most we will say about arrays for now
Reference Types - Class
• The concept of class as you know is the fundamental construct upon which
Java is built.
• A class serves as a blueprint or a template for a certain type of object.
• All data types other than the primitive type or the array must be addressed in
terms of class.
• This is evident in the way that we have been using class.
• For instance, going back to the class Book.
• In order to use this class we had to declare variables of the type:
• That is, Book b1; for instance
Reference Types - Standard Packages
• Java has a vast and rich collection of classes.
• These classes are stored in respective directories and subdirectories.
• Each directory or subdirectory is called, a package.
• Programmers can use these classes in their specific applications.
• There are several packages in Java.
• Two of the most important packages in the language are java and javax.
Java Standard Packages
java and javax packages, along with
their sub-packages. Some of the sub-
packages also contain sub-packages
of their own
•The sub-package lang is a special
package is for general programming
•The sub-package javax is designed
for Graphical User Interface
programming (GUI)
Java Standard Package- lang
• The java.lang package contains classes that are fundamental to Java.
• All of the classes in this package are available in your program automatically.
• That is, as soon as the Java compiler is loaded, all of these classes are loaded
into every Java source file.
Java Standard Package- lang
Java Standard Package- lang
• Chief among these fundamental classes are the following:
Object
String
Math
System
• The wrapper classes - for each primitive type there is a corresponding class.
Byte
Short
Integer
Long
Character
Float
Double
Boolean
Void
The class Object
• See the Application Programmers’ Interface (API)