Java Programming for Android Developers For Dummies, 2nd Edition

459 Pages·2016·13.48 MB·English

by  Barry A. Burd

Java® Programming
®
for Android
Developers
2nd edition
by Barry Burd
Java® Programming for Android® Developers For Dummies®, 2nd Edition
Published by: John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, www.wiley.com
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Library of Congress Control Number: 2016954409
ISBN: 978-1-119-30108-0; 978-1-119-30109-7 (ebk); 978-1-119-30112-7 (ebk)
Manufactured in the United States of America
10 9 8 7 6 5 4 3 2 1
Contents at a Glance
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Part 1: Getting Started with Java Programming
for Android Developers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
CHAPTER 1: All about Java and Android . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
CHAPTER 2: Getting the Tools That You Need . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
CHAPTER 3: Creating and Running an Android App . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Part 2: Writing Your Own Java Programs . . . . . . . . . . . . . . . . . . . . . 95
CHAPTER 4: An Ode to Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
CHAPTER 5: Java’s Building Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
CHAPTER 6: Working with Java Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
CHAPTER 7: Though These Be Methods, Yet There Is Madness in’t . . . . . . . . . . . . . . 169
CHAPTER 8: What Java Does (and When) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Part 3: Working with the Big Picture:
Object-Oriented Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
CHAPTER 9: Why Object-Oriented Programming Is Like Selling Cheese . . . . . . . . . . 217
CHAPTER 10: Saving Time and Money: Reusing Existing Code . . . . . . . . . . . . . . . . . . . 267
Part 4: Powering Android with Java Code . . . . . . . . . . . . . . . . . . . 295
CHAPTER 11: The Inside Story . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
CHAPTER 12: Dealing with a Bunch of Things at a Time . . . . . . . . . . . . . . . . . . . . . . . . . 317
CHAPTER 13: An Android Social Media App . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
CHAPTER 14: Hungry Burds: A Simple Android Game . . . . . . . . . . . . . . . . . . . . . . . . . . 381
Part 5: The Part of Tens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
CHAPTER 15: Ten Ways to Avoid Mistakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
CHAPTER 16: Ten Websites for Developers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417

Table of Contents
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
How to Use This Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Conventions Used in This Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
What You Don’t Have to Read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Foolish Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
How This Book Is Organized . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Part 1: Getting Started with Java Programming for Android
Developers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Part 2: Writing Your Own Java Programs . . . . . . . . . . . . . . . . . . . . . . . 5
Part 3: Working with the Big Picture: Object-Oriented
Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Part 4: Powering Android with Java Code . . . . . . . . . . . . . . . . . . . . . . 5
Part 5: The Part of Tens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
More on the web! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Icons Used in This Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Beyond the Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Where to Go from Here . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
PART 1: GETTING STARTED WITH JAVA PROGRAMMING
FOR ANDROID DEVELOPERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
CHAPTER 1: All about Java and Android . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
The Consumer Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
The Many Faces of Android . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
The Developer Perspective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
XML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Linux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
From Development to Execution with Java . . . . . . . . . . . . . . . . . . . . . . . 20
What is a compiler? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
What is a virtual machine? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Java, Android, and Horticulture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
CHAPTER 2: Getting the Tools That You Need . . . . . . . . . . . . . . . . . . . . . 27
The Stuff You Need . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
If You Don’t Like to Read the Instructions . . . . . . . . . . . . . . . . . . . . . . . . 29
Getting This Book’s Sample Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Setting Up Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Setting Up Android Studio and the Android SDK . . . . . . . . . . . . . . . . . . 37
Launching the Android Studio IDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Opening One of This Book’s Sample Programs . . . . . . . . . . . . . . . . . . . 40
Table of Contents v
Using Android Studio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Starting up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
The main window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Things You Might Eventually Have to Do . . . . . . . . . . . . . . . . . . . . . . . . . 48
Installing new versions (and older versions) of Android . . . . . . . . . 49
Creating an Android virtual device . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
CHAPTER 3: Creating and Running an Android App . . . . . . . . . . . . . . 55
Creating Your First App . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
First things first . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Launching your first app . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
If the Emulator Doesn’t Behave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Running third-party emulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Testing apps on a physical device . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
The Project Tool Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
The app/manifests branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
The app/java branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
The app/res branches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
The Gradle scripts branch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Dragging, Dropping, and Otherwise Tweaking an App . . . . . . . . . . . . . 70
Creating the “look” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Coding the behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
What All That Java Code Does . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Finding the EditText and TextView components . . . . . . . . . . . . . . . . 88
Responding to a button click . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
The rest of the code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Going Pro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
PART 2: WRITING YOUR OWN JAVA PROGRAMS . . . . . . . . . . . 95
CHAPTER 4: An Ode to Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Hello, Android! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
The Java Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
The names of classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Why Java Methods Are Like Meals at a Restaurant . . . . . . . . . . . . . . . 105
What does Mom’s Restaurant have to do with Java? . . . . . . . . . . . 106
Method declaration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Method call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Method parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
The chicken or the egg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
How many parameters? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
Method declarations and method calls in
an Android program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
vi Java Programming for Android Developers For Dummies
Punctuating Your Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Comments are your friends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
What’s Barry’s excuse? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
All About Android Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Extending a class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Overriding methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
An activity’s workhorse methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
CHAPTER 5: Java’s Building Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Info Is As Info Does . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
Variable names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Type names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Assignments and initializations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Expressions and literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
How to string characters together . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Java’s primitive types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .140
Things You Can Do with Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
Add letters to numbers (Huh?) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
Java’s exotic assignment operators . . . . . . . . . . . . . . . . . . . . . . . . . . 146
True bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Java isn’t like a game of horseshoes . . . . . . . . . . . . . . . . . . . . . . . . . 148
Use Java’s logical operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Parenthetically speaking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
CHAPTER 6: Working with Java Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Working with Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Going from primitive types to strings . . . . . . . . . . . . . . . . . . . . . . . . 158
Going from strings to primitive types . . . . . . . . . . . . . . . . . . . . . . . . 159
Getting input from the user . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Practice Safe Typing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
Widening is good; narrowing is bad . . . . . . . . . . . . . . . . . . . . . . . . .165
Incompatible types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
Using a hammer to bang a peg into a hole . . . . . . . . . . . . . . . . . . .167
Though These Be Methods, Yet There
CHAPTER 7:
Is Madness in’t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
Minding Your Types When You Call a Method . . . . . . . . . . . . . . . . . . . 170
Method parameters and Java types . . . . . . . . . . . . . . . . . . . . . . . . . 173
If at first you don’t succeed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
Return types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
The great void . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
Displaying numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
Primitive Types and Pass-by Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
What’s a developer to do? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
A final word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
Table of Contents vii
CHAPTER 8: What Java Does (and When) . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Making Decisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .187
Java if statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
Choosing among many alternatives . . . . . . . . . . . . . . . . . . . . . . . . . 191
Some formalities concerning Java switch statements . . . . . . . . . . 198
Repeating Instructions Over and Over Again . . . . . . . . . . . . . . . . . . . . 199
Check, and then repeat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .200
Repeat, and then check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
Count, count, count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
What’s Next? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
PART 3: WORKING WITH THE BIG PICTURE:
OBJECT-ORIENTED PROGRAMMING . . . . . . . . . . . . . . . . . . . . . . . . . 215
Why Object-Oriented Programming
CHAPTER 9:
Is Like Selling Cheese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
Classes and Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
What is a class, really? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
What is an object? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Creating objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
Reusing names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
Calling a constructor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
More About Classes and Objects (Adding Methods to the Mix) . . . . . 232
Constructors with parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .235
The default constructor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
This is it! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
Giving an object more responsibility . . . . . . . . . . . . . . . . . . . . . . . . 242
Members of a class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
Reference types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
Pass by reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
Java’s Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
Public classes and default-access classes . . . . . . . . . . . . . . . . . . . . 251
Access for fields and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
Using getters and setters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
What does static mean? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
To dot, or not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
A bad example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .264
What’s Next? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
Saving Time and Money: Reusing
CHAPTER 10:
Existing Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
The Last Word on Employees — Or Is It? . . . . . . . . . . . . . . . . . . . . . . . . 268
Extending a class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
Overriding methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
viii Java Programming for Android Developers For Dummies