2.29 Jb0240: java oop: arrays and strings

Revised: Mon Mar 28 16:20:59 CDT 2016

This page is included in the following Books:

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

Table of contents

• Preface
  • Viewing tip
    • Figures
    • Listings
• Introduction
• Arrays
• Arrays of Objects
• Strings
  • String Concatenation
  • Arrays of String References
• Run the programs
• Looking ahead
• Miscellaneous

Preface

This module takes a preliminary look at arrays and strings. More in-depth discussions will be provided in future modules. For example, you will find a more in-depth discussions of array objects in the followingmodules:

• Java OOP: Array Objects, Part 1
• Java OOP: Array Objects, Part 2
• Java OOP: Array Objects, Part 3

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the Figuresand Listings while you are reading about them.

Figures

• Figure 1 . Formats for declaring a reference variable for an array object.
• Figure 2 . Allocating memory for the array object.
• Figure 3 . Declaration and instantiation can be separated.
• Figure 4 . General syntax for combining declaration and instantiation.
• Figure 5 . An example of array indexing syntax.
• Figure 6 . The use of the length property in the conditional clause of a for loop.
• Figure 7 . A string literal.
• Figure 8 . String concatenation.
• Figure 9 . Declaring and instantiating a String array.
• Figure 10 . Allocating memory to contain the String objects.

Listings

• Listing 1 . The program named array01.
• Listing 2 . The program named array02.
• Listing 3 . The program named array03.

Introduction

The first step

The first step in learning to use a new programming language is usually to learn the foundation concepts such as variables, types,expressions, flow-of-control, arrays, strings, etc. This module concentrates on arrays and strings.

Array and String types

Java provides a type for both arrays and strings from which objects of the specific type can be instantiated. Once instantiated, the methodsbelonging to those types can be called by way of the object.

Arrays

Arrays and Strings

Java has a true array type and a true String type with protective features to prevent your program from writing outside the memorybounds of the array object or the String object. Arrays and strings are true objects.

Declaring an array

You must declare an array before you can use it. (More properly, you must declare a reference variable to hold a reference to the array object.) In declaring the array, you must provide two important pieces of information:

• the name of a variable to hold a reference to the array object
• the type of data to be stored in the elements of the array object

Different declaration formats

A reference variable capable of holding a reference to an array object can be declared using either format shown in Figure 1 . (I personally prefer the first option because I believe it is more indicative ofthe purpose of the declaration. However, both options produce the same result -- a reference variable capable of storing a reference to an array object.)