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<br /><b>Lesson:</b> Classes and Objects

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<div class="linkAHEAD"><a href="classes.html">Classes</a></div>

<div class="linkBHEAD"><a href="classdecl.html">Declaring Classes</a></div>

<div class="nolinkBHEAD">Declaring Member Variables</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&#151;these are called <i>fields</i>.</li>

<li>Variables in a method or block of code&#151;these are called <i>local variables</i>.</li>

<li>Variables in method declarations&#151;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&#39;s type.</li>

<li>The field&#39;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&#151;the field is accessible from all classes.</li>

<li><code>private</code> modifier&#151;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&#151;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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