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<br /><b>Section:</b> Classes
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<div class="linkBHEAD"><a href="classdecl.html">Declaring Classes</a></div>
<div class="nolinkBHEAD">Declaring Member Variables</div>
<div class="linkBHEAD"><a href="methods.html">Defining Methods</a></div>
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<div id="PageTitle"><h1>Declaring Member Variables</h1></div>
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<!-- Declaring Member fields -->
<p>There are several kinds of variables:</p>
<ul>
<li>Member variables in a class—these are called <i>fields</i>.</li>
<li>Variables in a method or block of code—these are called <i>local variables</i>.</li>
<li>Variables in method declarations—these are called <i>parameters</i>.</li>
</ul>
<p>The <code>Bicycle</code> class uses the following lines of code to define its fields:</p>
<div class="codeblock"><pre>
public int cadence;
public int gear;
public int speed;
</pre></div>
<p>Field declarations are composed of three components, in order:</p>
<ol>
<li>Zero or more modifiers, such as <code>public</code> or <code>private</code>.</li>
<li>The field's type.</li>
<li>The field's name.</li>
</ol>
<p>The fields of <code>Bicycle</code> are named <code>cadence</code>, <code>gear</code>, and <code>speed</code> and are all of data type integer (<code>int</code>). The <code>public</code> keyword identifies these fields as public members, accessible by any object that can access the class.</p>
<h2>Access Modifiers</h2>
<p>The first (left-most) modifier used lets you control what other classes have access to a member field. For the moment, consider only <code>public</code> and <code>private</code>. Other access modifiers will be discussed later.</p>
<ul>
<li><code>public</code> modifier—the field is accessible from all classes.</li>
<li><code>private</code> modifier—the field is accessible only within its own class.</li>
</ul>
<p>In the spirit of encapsulation, it is common to make fields private. This means that they can only be <i>directly</i> accessed from the Bicycle class. We still need access to these values, however. This can be done <i>indirectly</i> by adding public methods that obtain the field values for us:</p>
<div class="codeblock"><pre>
public class Bicycle {
private int cadence;
private int gear;
private int speed;
public Bicycle(int startCadence, int startSpeed, int startGear) {
gear = startGear;
cadence = startCadence;
speed = startSpeed;
}
public int getCadence() {
return cadence;
}
public void setCadence(int newValue) {
cadence = newValue;
}
public int getGear() {
return gear;
}
public void setGear(int newValue) {
gear = newValue;
}
public int getSpeed() {
return speed;
}
public void applyBrake(int decrement) {
speed -= decrement;
}
public void speedUp(int increment) {
speed += increment;
}
}
</pre></div>
<h2>Types</h2>
<p>All variables must have a type. You can use primitive types such as <code>int</code>, <code>float</code>, <code>boolean</code>, etc. Or you can use reference types, such as strings, arrays, or objects.</p>
<h2>Variable Names</h2>
<p>All variables, whether they are fields, local variables, or parameters, follow the same naming rules and conventions that were covered in the Language Basics
lesson,
<a class="TutorialLink" target="_top" href="../../java/nutsandbolts/variables.html#naming">Variables—Naming</a>.</p>
<p>In this
lesson,
be aware that the same naming rules and conventions are used for method and class names, except that</p>
<ul>
<li>the first letter of a class name should be capitalized, and</li>
<li>the first (or only) word in a method name should be a verb.</li>
</ul>
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