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<b>Trail:</b> Learning the Java Language

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

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<div class="linkLESSON"><a href="index.html">Classes and Objects</a></div>

<div class="nolinkAHEAD">Classes</div>

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

<div class="linkBHEAD"><a href="variables.html">Declaring Member Variables</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>

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<div id="PageTitle"><h1>Classes</h1></div>

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<p>The introduction to object-oriented concepts in the lesson titled

<a class="TutorialLink" target="_top" href="../../java/concepts/index.html">Object-oriented Programming Concepts </a>used a bicycle class as an example, with racing bikes, mountain bikes, and tandem bikes as subclasses. Here is sample code for a possible implementation of a <code>Bicycle</code> class, to give you an overview of a class declaration. Subsequent sections of this

lesson

will back up and explain class declarations step by step. For the moment, don&#39;t concern yourself with the details.</p>

<div class="codeblock"><pre>

public class Bicycle {

// <b>the Bicycle class has</b>

// <b>three <i>fields</i></b>

public int cadence;

public int gear;

public int speed;

// <b>the Bicycle class has</b>

// <b>one <i>constructor</i></b>

public Bicycle(int startCadence, int startSpeed, int startGear) {

gear = startGear;

cadence = startCadence;

speed = startSpeed;

}

// <b>the Bicycle class has</b>

// <b>four <i>methods</i></b>

public void setCadence(int newValue) {

cadence = newValue;

}

public void setGear(int newValue) {

gear = newValue;

}

public void applyBrake(int decrement) {

speed -= decrement;

}

public void speedUp(int increment) {

speed += increment;

}

}

</pre></div>

<p>A class declaration for a <code>MountainBike</code> class that is a subclass of <code>Bicycle</code> might look like this:</p>

<div class="codeblock"><pre>

public class MountainBike extends Bicycle {

// <b>the MountainBike subclass has</b>

// <b>one <i>field</i></b>

public int seatHeight;

// <b>the MountainBike subclass has</b>

// <b>one <i>constructor</i></b>

public MountainBike(int startHeight, int startCadence,

int startSpeed, int startGear) {

super(startCadence, startSpeed, startGear);

seatHeight = startHeight;

}

// <b>the MountainBike subclass has</b>

// <b>one <i>method</i></b>

public void setHeight(int newValue) {

seatHeight = newValue;

}

}

</pre></div>

<p><code>MountainBike</code> inherits all the fields and methods of <code>Bicycle</code> and adds the field <code>seatHeight</code> and a method to set it (mountain bikes have seats that can be moved up and down as the terrain demands).</p>

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