forked from ashishjohn1908/Java
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathreturnvalue.html
More file actions
532 lines (499 loc) · 19.5 KB
/
Copy pathreturnvalue.html
File metadata and controls
532 lines (499 loc) · 19.5 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
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
<?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>Returning a Value from a Method (The Java™ Tutorials >
Learning the Java Language > Classes and Objects)
</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> Classes and Objects
<br /><b>Section:</b> More on Classes
</div>
<div id="LeftBar" class="LeftBar_shown">
<div id="Contents">
<div class="linkLESSON"><a href="index.html">Classes and Objects</a></div>
<div class="linkAHEAD"><a href="classes.html">Classes</a></div>
<div class="linkBHEAD"><a href="classdecl.html">Declaring Classes</a></div>
<div class="linkBHEAD"><a href="variables.html">Declaring Member Variables</a></div>
<div class="linkBHEAD"><a href="methods.html">Defining Methods</a></div>
<div class="linkBHEAD"><a href="constructors.html">Providing Constructors for Your Classes</a></div>
<div class="linkBHEAD"><a href="arguments.html">Passing Information to a Method or a Constructor</a></div>
<div class="linkAHEAD"><a href="objects.html">Objects</a></div>
<div class="linkBHEAD"><a href="objectcreation.html">Creating Objects</a></div>
<div class="linkBHEAD"><a href="usingobject.html">Using Objects</a></div>
<div class="linkAHEAD"><a href="more.html">More on Classes</a></div>
<div class="nolinkBHEAD">Returning a Value from a Method</div>
<div class="linkBHEAD"><a href="thiskey.html">Using the this Keyword</a></div>
<div class="linkBHEAD"><a href="accesscontrol.html">Controlling Access to Members of a Class</a></div>
<div class="linkBHEAD"><a href="classvars.html">Understanding Class Members</a></div>
<div class="linkBHEAD"><a href="initial.html">Initializing Fields</a></div>
<div class="linkBHEAD"><a href="summaryclasses.html">Summary of Creating and Using Classes and Objects</a></div>
<div class="linkQUESTIONS"><a href="QandE/creating-questions.html">Questions and Exercises</a></div>
<div class="linkQUESTIONS"><a href="QandE/objects-questions.html">Questions and Exercises</a></div>
<div class="linkAHEAD"><a href="nested.html">Nested Classes</a></div>
<div class="linkBHEAD"><a href="innerclasses.html">Inner Class Example</a></div>
<div class="linkBHEAD"><a href="localclasses.html">Local Classes</a></div>
<div class="linkBHEAD"><a href="anonymousclasses.html">Anonymous Classes</a></div>
<div class="linkBHEAD"><a href="lambdaexpressions.html">Lambda Expressions</a></div>
<div class="linkCHEAD"><a href="methodreferences.html">Method References</a></div>
<div class="linkBHEAD"><a href="whentouse.html">When to Use Nested Classes, Local Classes, Anonymous Classes, and Lambda Expressions </a></div>
<div class="linkQUESTIONS"><a href="QandE/nested-questions.html">Questions and Exercises</a></div>
<div class="linkAHEAD"><a href="enum.html">Enum Types</a></div>
<div class="linkQUESTIONS"><a href="QandE/enum-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">Classes and Objects</a>
</span>
<div class="NavBit">
<a target="_top" href="more.html">« Previous</a> • <a target="_top" href="../TOC.html">Trail</a> • <a target="_top" href="thiskey.html">Next »</a>
</div>
<div id="PageTitle"><h1>Returning a Value from a Method</h1></div>
<div id="PageContent">
<!-- Returning a Value from a Method -->
<p>A method returns to the code that invoked it when it</p>
<ul>
<li>completes all the statements in the method,</li>
<li>reaches a <code>return</code> statement, or</li>
<li>throws an exception (covered later),</li>
</ul>
<p>whichever occurs first.</p>
<p>You declare a method's return type in its method declaration. Within the body of the method, you use the <code>return</code> statement to return the value.</p>
<p>Any method declared <code>void</code> doesn't return a value. It does not need to contain a <code>return</code> statement, but it may do so. In such a case, a <code>return</code> statement can be used to branch out of a control flow block and exit the method and is simply used like this:</p>
<div class="codeblock"><pre>
return;
</pre></div>
<p>If you try to return a value from a method that is declared <code>void</code>, you will get a compiler error.</p>
<p>Any method that is not declared <code>void</code> must contain a <code>return</code> statement with a corresponding return value, like this:</p>
<div class="codeblock"><pre>
return returnValue;
</pre></div>
<p>The data type of the return value must match the method's declared return type; you can't return an integer value from a method declared to return a boolean.</p>
<p>The <code>getArea()</code> method in the <code>Rectangle</code>
<a class="SourceLink" target="_blank" href="examples/Rectangle.java" onclick="showCode('../../displayCode.html', 'examples/Rectangle.java'); return false;"><code>Rectangle</code></a> class that was discussed in the sections on objects returns an integer:</p>
<div class="codeblock"><pre>
// a method for computing the area of the rectangle
public int getArea() {
return width * height;
}
</pre></div>
<p>This method returns the integer that the expression <code>width*height</code> evaluates to.</p>
<p>The <code>getArea</code> method returns a primitive type. A method can also return a reference type. For example, in a program to manipulate <code>Bicycle</code> objects, we might have a method like this:</p>
<div class="codeblock"><pre>
public Bicycle seeWhosFastest(Bicycle myBike, Bicycle yourBike,
Environment env) {
Bicycle fastest;
// code to calculate which bike is
// faster, given each bike's gear
// and cadence and given the
// environment (terrain and wind)
return fastest;
}
</pre></div>
<h2>Returning a Class or Interface</h2>
<p>If this section confuses you, skip it and return to it after you have finished the
lesson
on interfaces and inheritance.</p>
<p>When a method uses a class name as its return type, such as <code>whosFastest</code> does, the class of the type of the returned object must be either a subclass of, or the exact class of, the return type. Suppose that you have a class hierarchy in which <code>ImaginaryNumber</code> is a subclass of <code>java.lang.Number</code>, which is in turn a subclass of <code>Object</code>, as illustrated in
<span id="figure:classes-hierarchy.gif">the following figure</span>.</p>
<center><img src="../../figures/java/classes-hierarchy.gif" width="130" height="136" align="bottom" alt="The class hierarchy for ImaginaryNumber" /></p><p class="FigureCaption">The class hierarchy for ImaginaryNumber</p></center><p>Now suppose that you have a method declared to return a <code>Number</code>:</p>
<div class="codeblock"><pre>
public Number returnANumber() {
...
}
</pre></div>
<p>The <code>returnANumber</code> method can return an <code>ImaginaryNumber</code> but not an <code>Object</code>. <code>ImaginaryNumber</code> is a <code>Number</code> because it's a subclass of <code>Number</code>. However, an <code>Object</code> is not necessarily a <code>Number</code> — it could be a <code>String</code> or another type.</p>
<p>You can override a method and define it to return a subclass of the original method, like this:</p>
<div class="codeblock"><pre>
public ImaginaryNumber returnANumber() {
...
}
</pre></div>
<p>This technique, called <em>covariant return type</em>, means that the return type is allowed to vary in the same direction as the subclass.</p>
<div class="note"><hr /><strong>Note:</strong> You also can use interface names as return types. In this case, the object returned must implement the specified interface.
<hr /></div>
</div>
<div class="NavBit">
<a target="_top" href="more.html">« Previous</a>
•
<a target="_top" href="../TOC.html">Trail</a>
•
<a target="_top" href="thiskey.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> More on Classes
<br /><b>Next page:</b> Using the this Keyword
</div>
</body>
</html>