forked from ashishjohn1908/Java
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathobject.html
More file actions
461 lines (429 loc) · 17.4 KB
/
Copy pathobject.html
File metadata and controls
461 lines (429 loc) · 17.4 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html lang="en-US" xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>What Is an Object? (The Java™ Tutorials >
Learning the Java Language > Object-Oriented Programming Concepts)
</title>
<meta name="description" content="This beginner Java tutorial describes fundamentals of programming in the Java programming language" />
<meta name="keywords" content="java programming, learn java, java sample code, java objects, java classes, java inheritance, interfaces, variables, arrays, data types, operators, control flow, number, string" />
<style type="text/css">
.FigureCaption {
margin-left: 1in;
margin-right: 1in;
font-family: sans-serif;
font-size: smaller;
text-align: justify;
}
#TopBar_bl {
background: url(../../images/java_bar_bl.gif) 0 100% no-repeat;
width: 100%;
height: 60px;
}
#TopBar_br {
background: url(../../images/java_bar_br.gif) 100% 100% no-repeat;
width: 100%;
height: 60px;
}
#TopBar_tl {
background: url(../../images/java_bar_tl.gif) 0 0 no-repeat;
width: 100%;
height: 60px;
}
#TopBar_tr {
background: url(../../images/java_bar_tr.gif) 100% 0 no-repeat;
width: 100%;
height: 60px;
}
#TopBar {
background: #35556B url(../../images/java_bar.gif);
margin: 10px 10px 0 10px;
height:60px;
min-width:700px;
color: white;
font-family: sans-serif;
font-weight: bold;
}
@media print {
#BreadCrumbs, #Download {
display: none;
}
}
#TopBar_right {
line-height: 14px;
float: right;
padding-top: 2px;
padding-right: 30px;
text-align: left;
}
@media print {
#TopBar_right {
display: none;
}
}
#TopBar_right a {
font-size: 12px;
margin: 3px;
padding: 0;
}
#TopBar a:visited, #TopBar a:link {
color: white;
text-decoration: none;
}
#TopBar a:hover, #TopBar a:active {
background-color: white;
color: #35556B;
}
#BreadCrumbs {
padding: 4px 5px 0.5em 0;
font-family: sans-serif;
float: right;
}
#BreadCrumbs a {
color: blue;
}
#BreadCrumbs a:visited, #BreadCrumbs a:link {
text-decoration: none;
}
#BreadCrumbs a:hover, #BreadCrumbs a:active {
text-decoration: underline;
}
#PageTitle {
margin: 0 5px 0.5em 0;
color: #F90000;
}
#PageContent{
margin: 0 5px 0 20px;
}
.LeftBar_shown {
width: 13em;
float: left;
margin-left: 10px;
margin-top: 4px;
margin-bottom: 2em;
margin-right: 10px;
}
@media print {
.LeftBar_shown {
display: none;
}
}
.LeftBar_hidden {
display: none;
}
#Footer {
padding-top: 10px;
padding-left: 10px;
margin-right: 10px;
}
.footertext {
font-size: 10px;
font-family: sans-serif;
margin-top: 1px;
}
#Footer2 {
padding-top: 10px;
padding-left: 10px;
margin-right: 10px;
}
.NavBit {
padding: 4px 5px 0.5em 0;
font-family: sans-serif;
}
@media print {
.NavBit {
display: none;
}
}
#TagNotes {
text-align: right;
}
@media print {
#TagNotes a:visited, #TagNotes a:link {
color: #35556B;
text-decoration: none;
}
}
#Contents a, .NavBit a, #TagNotes a {
color: blue
}
#TagNotes a:visited, #TagNotes a:link,
#Contents a:visited, #Contents a:link,
.NavBit a:visited, .NavBit a:link {
text-decoration: none;
}
#TagNotes a:hover, #TagNotes a:active,
#Contents a:hover, #Contents a:active,
.NavBit a:hover, .NavBit a:active {
text-decoration: underline;
}
#Contents {
float: left;
font-family: sans-serif;
}
@media print {
#Contents {
display: none;
}
}
@media screen {
div.PrintHeaders {
display: none;
}
}
.linkLESSON, .nolinkLESSON {
margin-left: 0.5em;
text-indent: -0.5em
}
.linkAHEAD, .nolinkAHEAD, .linkQUESTIONS, .nolinkQUESTIONS {
margin-left: 1.5em;
text-indent: -0.5em
}
.linkBHEAD, .nolinkBHEAD {
margin-left: 2.5em;
text-indent: -0.5em
}
.linkCHEAD, .nolinkCHEAD {
margin-left: 3.5em;
text-indent: -0.5em
}
.nolinkLESSON, .nolinkAHEAD, .nolinkBHEAD, .nolinkCHEAD,
.nolinkQUESTIONS {
font-weight: bold;
color: #F90000;
}
.MainFlow_indented {
margin-right: 10px;
margin-left: 15em;
margin-bottom: 2em;
}
.MainFlow_wide {
margin-right: 10px;
margin-left: 10px;
margin-bottom: 2em;
}
@media print {
.MainFlow_indented, .MainFlow_wide {
padding-top: 0;
margin-top: 10px;
margin-right: 10px;
margin-left: 0;
}
}
h1, h2, h3, h4, h5 {
color: #F90000;
font-family: sans-serif;
}
h1 {
font-weight: bold;
font-size: 20px;
}
h2 {
font-weight: bold;
font-size: 17px;
}
h3 {
font-weight: bold;
font-size: 14px;
}
h4 {
font-size: 15px;
}
h5 {
font-size: 12px;
}
#ToggleLeft {
display: none;
}
.note {
margin: 0 30px 0px 30px;
}
.codeblock {
margin: 0 30px 0px 30px;
}
.tocli {
list-style-type:none;
}
.betadraft {
color: red;
}
</style>
<script type="text/javascript">
/* <![CDATA[ */
function leftBar() {
var nameq = 'tutorial_showLeftBar='
var cookies = document.cookie.split(';');
for (var i = 0; i < cookies.length; i++) {
var cookieString = cookies[i];
while (cookieString.charAt(0) == ' ') {
cookieString = cookieString.substring(1, cookieString.length);
}
if (cookieString.indexOf(nameq) == 0) {
cookieValue = cookieString.substring(nameq.length,
cookieString.length);
return cookieValue == 'yes';
}
}
return true;
}
function showLeft(b) {
var contents = document.getElementById("LeftBar");
var main = document.getElementById("MainFlow");
var toggle = document.getElementById("ToggleLeft");
if (b) {
contents.className = "LeftBar_shown";
main.className = "MainFlow_indented";
toggle.innerHTML = "Hide TOC";
document.cookie = 'tutorial_showLeftBar=yes; path=/';
} else {
contents.className = "LeftBar_hidden";
main.className = "MainFlow_wide";
toggle.innerHTML = "Show the TOC";
document.cookie = 'tutorial_showLeftBar=no; path=/';
}
}
function toggleLeft() {
showLeft(document.getElementById("LeftBar").className ==
"LeftBar_hidden");
document.getElementById("ToggleLeft").blur();
}
function load() {
showLeft(leftBar());
document.getElementById("ToggleLeft").style.display="inline";
}
function showCode(displayCodePage, codePath) {
var codePathEls = codePath.split("/");
var currDocPathEls = location.href.split("/");
//alert ("codePathEls = " + codePathEls + "\n" + "currDocPathEls = " + currDocPathEls);
currDocPathEls.pop(); // remove file name at the end
while (codePathEls.length > 0) {
if (codePathEls[0] == "..") {
codePathEls.shift();
currDocPathEls.pop();
} else {
break;
}
}
var fullCodePath = currDocPathEls.join("/") + "/" + codePathEls.join("/");
//alert ("fullCodePath = " + fullCodePath );
if (codePath.indexOf(".java") != -1 || codePath.indexOf(".jnlp") != -1) {
window.location.href = displayCodePage + "?code=" + encodeURI(fullCodePath);
} else {
window.location.href = fullCodePath;
}
}
/* ]]> */
</script>
</head>
<body onload="load()">
<noscript>
A browser with JavaScript enabled is required for this page to operate properly.
</noscript>
<div id="TopBar"> <div id="TopBar_tr"> <div id="TopBar_tl"> <div id="TopBar_br"> <div id="TopBar_bl">
<div id="TopBar_right">
<a target="_blank"
href="http://www.oracle.com/technetwork/java/javase/downloads/java-se-7-tutorial-2012-02-28-1536013.html">Download Ebooks</a><br />
<a target="_blank"
href="http://www.oracle.com/technetwork/java/javase/downloads/index.html">Download JDK</a>
<br />
<a href="../../search.html" target="_blank">Search Java Tutorials</a>
<br />
<a href="javascript:toggleLeft()"
id="ToggleLeft">Hide TOC</a>
</div>
</div> </div> </div> </div> </div>
<div class="PrintHeaders">
<b>Trail:</b> Learning the Java Language
<br /><b>Lesson:</b> Object-Oriented Programming Concepts
</div>
<div id="LeftBar" class="LeftBar_shown">
<div id="Contents">
<div class="linkLESSON"><a href="index.html">Object-Oriented Programming Concepts</a></div>
<div class="nolinkAHEAD">What Is an Object?</div>
<div class="linkAHEAD"><a href="class.html">What Is a Class?</a></div>
<div class="linkAHEAD"><a href="inheritance.html">What Is Inheritance?</a></div>
<div class="linkAHEAD"><a href="interface.html">What Is an Interface?</a></div>
<div class="linkAHEAD"><a href="package.html">What Is a Package?</a></div>
<div class="linkQUESTIONS"><a href="QandE/questions.html">Questions and Exercises</a></div>
</div>
</div>
<div id="MainFlow" class="MainFlow_indented">
<span id="BreadCrumbs">
<a href="../../index.html" target="_top">Home Page</a>
>
<a href="../index.html" target="_top">Learning the Java Language</a>
>
<a href="index.html" target="_top">Object-Oriented Programming Concepts</a>
</span>
<div class="NavBit">
<a target="_top" href="index.html">« Previous</a> • <a target="_top" href="../TOC.html">Trail</a> • <a target="_top" href="class.html">Next »</a>
</div>
<div id="PageTitle"><h1>What Is an Object?</h1></div>
<div id="PageContent">
<p>Objects are key to understanding <i>object-oriented</i> technology. Look around right now and you'll find many examples of real-world objects: your dog, your desk, your television set, your bicycle.</p>
<p>Real-world objects share two characteristics: They all have <i>state</i> and <i>behavior</i>. Dogs have state (name, color, breed, hungry) and behavior (barking, fetching, wagging tail). Bicycles also have state (current gear, current pedal cadence, current speed) and behavior (changing gear, changing pedal cadence, applying brakes). Identifying the state and behavior for real-world objects is a great way to begin thinking in terms of object-oriented programming.</p>
<p>Take a minute right now to observe the real-world objects that are in your immediate area. For each object that you see, ask yourself two questions: "What possible states can this object be in?" and "What possible behavior can this object perform?". Make sure to write down your observations. As you do, you'll notice that real-world objects vary in complexity; your desktop lamp may have only two possible states (on and off) and two possible behaviors (turn on, turn off), but your desktop radio might have additional states (on, off, current volume, current station) and behavior (turn on, turn off, increase volume, decrease volume, seek, scan, and tune). You may also notice that some objects, in turn, will also contain other objects. These real-world observations all translate into the world of object-oriented programming.</p>
<center><img src="../../figures/java/concepts-object.gif" width="345" height="210" align="bottom" alt="A circle with an inner circle filled with items, surrounded by gray wedges representing methods that allow access to the inner circle." /></p><p class="FigureCaption">A software object.</p></center><br />
<p>Software objects are conceptually similar to real-world objects: they too consist of state and related behavior. An object stores its state in <i>fields</i> (variables in some programming languages) and exposes its behavior through <i>methods</i> (functions in some programming languages). Methods operate on an object's internal state and serve as the primary mechanism for object-to-object communication. Hiding internal state and requiring all interaction to be performed through an object's methods is known as <i>data encapsulation</i> — a fundamental principle of object-oriented programming.</p>
<p>Consider a bicycle, for example:</p>
<center><img src="../../figures/java/concepts-bicycleObject.gif" width="273" height="218" align="bottom" alt="A picture of an object, with bibycle methods and instance variables." /></p><p class="FigureCaption">A bicycle modeled as a software object.</p></center><br />
<p>By attributing state (current speed, current pedal cadence, and current gear) and providing methods for changing that state, the object remains in control of how the outside world is allowed to use it. For example, if the bicycle only has 6 gears, a method to change gears could reject any value that is less than 1 or greater than 6.</p>
<p>Bundling code into individual software objects provides a number of benefits, including:</p>
<ol>
<li>Modularity: The source code for an object can be written and maintained independently of the source code for other objects. Once created, an object can be easily passed around inside the system.</li>
<li>Information-hiding: By interacting only with an object's methods, the details of its internal implementation remain hidden from the outside world.</li>
<li>Code re-use: If an object already exists (perhaps written by another software developer), you can use that object in your program. This allows specialists to implement/test/debug complex, task-specific objects, which you can then trust to run in your own code.</li>
<li>Pluggability and debugging ease: If a particular object turns out to be problematic, you can simply remove it from your application and plug in a different object as its replacement. This is analogous to fixing mechanical problems in the real world. If a bolt breaks, you replace <i>it</i>, not the entire machine.</li>
</ol>
</div>
<div class="NavBit">
<a target="_top" href="index.html">« Previous</a>
•
<a target="_top" href="../TOC.html">Trail</a>
•
<a target="_top" href="class.html">Next »</a>
</div>
</div>
<div id="Footer2">
<hr />
<div id="TagNotes">
<p class="footertext">Problems with the examples? Try <a target="_blank"
href="../../information/run-examples.html">Compiling and Running
the Examples: FAQs</a>.
<br />
Complaints? Compliments? Suggestions? <a target="_blank"
href="http://docs.oracle.com/javase/feedback.html">Give
us your feedback</a>.
</p>
</div>
<div id="Footer">
<p class="footertext"><a name="license_info">Your use of this</a> page and all the material on pages under "The Java Tutorials" banner
is subject to these <a href="../../information/cpyr.html">legal notices</a>.
</p>
<table border="0" cellspacing="0" cellpadding="5" summary="">
<tr>
<td width="20%">
<table width="100%" border="0" cellspacing="0" cellpadding="5">
<tr>
<td headers="h1" align="center"><img id="duke" src="../../images/DukeWave.gif" width="55" height="55" alt="duke image" /></td>
<td headers="h2" align="left" valign="middle"><img id="oracle" src="../../images/logo_oracle_footer.gif" width="100" height="29" alt="Oracle logo" /></td>
</tr>
</table>
</td>
<td width="55%" valign="middle" align="center">
<p class="footertext"><a href="http://www.oracle.com/us/corporate/index.html">About Oracle</a> | <a href="http://www.oracle.com/technology/index.html">Oracle Technology Network</a> | <a href="http://www.oracle.com/us/legal/terms/index.html">Terms of Use</a></p>
</td>
<td width="25%" valign="middle" align="right">
<p class="footertext">Copyright © 1995, 2014 Oracle and/or its affiliates. All rights reserved.</p>
</td>
</tr>
</table>
</div>
</div>
<div class="PrintHeaders">
<b>Previous page:</b> Object-Oriented Programming Concepts
<br /><b>Next page:</b> What Is a Class?
</div>
</body>
</html>