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<b>Trail:</b> Learning the Java Language
<br /><b>Lesson:</b> Classes and Objects
<br /><b>Section:</b> Classes
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<div class="linkLESSON"><a href="index.html">Classes and Objects</a></div>
<div class="linkAHEAD"><a href="classes.html">Classes</a></div>
<div class="nolinkBHEAD">Declaring Classes</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>
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<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="linkBHEAD"><a href="returnvalue.html">Returning a Value from a Method</a></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>
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<div id="PageTitle"><h1>Declaring Classes</h1></div>
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<!-- Declaring Classes -->
<p>You've seen classes defined in the following way:</p>
<div class="codeblock"><pre>
class <i>MyClass</i> {
// field, constructor, and
// method declarations
}
</pre></div>
<p>This is a <i>class declaration</i>. The <em>class body</em> (the area between the braces) contains all the code that provides for the life cycle of the objects created from the class: constructors for initializing new objects, declarations for the fields that provide the state of the class and its objects, and methods to implement the behavior of the class and its objects.</p>
<p>The preceding class declaration is a minimal one. It contains only those components of a class declaration that are required. You can provide more information about the class, such as the name of its superclass, whether it implements any interfaces, and so on, at the start of the class declaration. For example,</p>
<div class="codeblock"><pre>
class <i>MyClass extends MySuperClass implements YourInterface</i> {
// field, constructor, and
// method declarations
}
</pre></div>
<p>means that <code>MyClass</code> is a subclass of <code>MySuperClass</code> and that it implements the <code>YourInterface</code> interface.</p>
<p>You can also add modifiers like <i>public</i> or <i>private</i> at the very beginning—so you can see that the opening line of a class declaration can become quite complicated. The modifiers <i>public</i> and <i>private</i>, which determine what other classes can access <code>MyClass</code>, are discussed later in this
lesson.
The lesson
on interfaces and inheritance will explain how and why you would use the <i>extends</i> and <i>implements</i> keywords in a class declaration. For the moment you do not need to worry about these extra complications.</p>
<p>In general, class declarations can include these components, in order:</p>
<ol>
<li>Modifiers such as <i>public</i>, <i>private</i>, and a number of others that you will encounter later.</li>
<li>The class name, with the initial letter capitalized by convention.</li>
<li>The name of the class's parent (superclass), if any, preceded by the keyword <i>extends</i>. A class can only <i>extend</i> (subclass) one parent.</li>
<li>A comma-separated list of interfaces implemented by the class, if any, preceded by the keyword <i>implements</i>. A class can <i>implement</i> more than one interface.</li>
<li>The class body, surrounded by braces, {}.</li>
</ol>
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