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SHAPE ="RECT" HREF ="/reference/author.html" COORDS ="361,0,440,29"><AREA SHAPE ="RECT" HREF ="/reference/basic.html" COORDS ="254,0,360,29"><AREA SHAPE ="RECT" HREF ="/reference/help.html" COORDS ="183,0,251,29"><AREA SHAPE ="RECT" HREF ="/reference/cool.html" COORDS ="100,0,181,29"><AREA SHAPE ="RECT" HREF ="/reference/mybook.html" COORDS ="0,0,100,29"></MAP><MAP NAME ="header_r1.gif.map"><AREA SHAPE ="RECT" HREF ="/reference/personalize.html" COORDS ="339,0,439,29"></MAP><p><font face="Arial,Helvetica" size="-1" color="#006666"><A HREF="/reference/r_library.html"><B>All Categories</A> :</B><b><A HREF="/reference/r_java.html">Java</A></b></font><p> <META NAME="GENERATOR" CONTENT="Mozilla/3.0b5aGold (WinNT; I) [Netscape]"><H1><FONT COLOR=#FF0000>Chapter 2</FONT></H1><H1><B><FONT SIZE=5 COLOR=#FF0000>Object-Oriented Development inJava</FONT></B></H1><P><HR WIDTH="100%"></P><P><H3 ALIGN=CENTER><FONT COLOR="#000000"><FONT SIZE=+2>CONTENTS<A NAME="CONTENTS"></A></FONT></FONT></H3><UL><LI><A HREF="#IntroductiontoJavaClassesandObjects" >Introduction to Java Classes and Objects</A><UL><LI><A HREF="#BasicStructureofaClass" >Basic Structure of a Class</A><LI><A HREF="#CreatinganObjectInstance" >Creating an Object Instance</A><LI><A HREF="#UsingMethods" >Using Methods</A><LI><A HREF="#OverloadingMethods" >Overloading Methods</A><LI><A HREF="#Constructors" >Constructors</A></UL><LI><A HREF="#InheritanceinJava" >Inheritance in Java</A><UL><LI><A HREF="#Subclassing" >Subclassing</A><LI><A HREF="#MethodOverriding" >Method Overriding</A><LI><A HREF="#CallingSuperclassMethods" >Calling Superclass Methods</A><LI><A HREF="#CallingSuperclassConstructors" >Calling Superclass Constructors</A></UL><LI><A HREF="#ImportantCoreClasses" >Important Core Classes</A><UL><LI><A HREF="#TheObjectBaseClass" >The Object Base Class</A><LI><A HREF="#StringClasses" >String Classes</A><LI><A HREF="#TypeWrappers" >Type Wrappers</A></UL><LI><A HREF="#MoreaboutClasses" >More about Classes</A><UL><LI><A HREF="#AccessModifiers" >Access Modifiers</A><LI><A HREF="#ClassMethodsandClassVariables" >Class Methods and Class Variables</A><LI><A HREF="#ThefinalModifier" >The final Modifier</A><LI><A HREF="#ThenullKeywordandMoreaboutGarbage" >The null Keyword and More about Garbage Collection</A><LI><A HREF="#ScopingRules" >Scoping Rules</A><LI><A HREF="#CastingRules" >Casting Rules</A><LI><A HREF="#OtherKeywords" >Other Keywords</A></UL><LI><A HREF="#IntroductiontoExceptionHandling" >Introduction to Exception Handling</A><UL><LI><A HREF="#StructureofanExceptionHandler" >Structure of an Exception Handler</A><LI><A HREF="#WhentoCatchExceptions" >When to Catch Exceptions</A><LI><A HREF="#ExceptionHandlersandExceptionClasses" >Exception Handlers and Exception Classes</A><LI><A HREF="#NestedExceptions" >Nested Exceptions</A></UL><LI><A HREF="#OrganizingProjectsinJava" >Organizing Projects in Java</A><UL><LI><A HREF="#AbstractMethods" >Abstract Methods</A><LI><A HREF="#Interfaces" >Interfaces</A><LI><A HREF="#Packages" >Packages</A></UL><LI><A HREF="#TheJavaDevelopersKit" >The Java Developer's Kit</A><LI><A HREF="#Summary" >Summary</A></UL><HR><P>Now that you're familiar with the general architecture of Javaand its basic programming constructs, you're ready to look atJava's tools for object-oriented development. This chapter firstlooks at the simple, yet powerful, object-oriented features ofthe Java programming language. You then see how you can organizeJava classes into libraries by using the <I>package</I> <I>mechanism</I>.Finally, you're introduced to the suite of class libraries providedwith Java, known as the <I>Java Developer's Kit</I> <I>(JDK)</I>or the <I>Java API</I>.<H2><A NAME="IntroductiontoJavaClassesandObjects"><FONT SIZE=5 COLOR=#FF0000>Introductionto Java Classes and Objects</FONT></A></H2><P>The starting place of object-oriented programming in Java is <I>classes</I>,which provide templates for specifying the state and behaviorof an object at runtime. An <I>object</I> is said to be an <I>instance</I>of a class. For a given class and runtime session, there can bemultiple object instances.<H3><A NAME="BasicStructureofaClass">Basic Structure of a Class</A></H3><P>A class generally consists of <I>variables</I> and <I>methods</I>.The following is a rudimentary example of a class called FirstClass:<BLOCKQUOTE><TT>class FirstClass {<BR> int firstVariable = 0; // Initially set to 0<BR> // Set the value of the variable...<BR> public void setValue(int newValue) {<BR> firstVariable = newValue;<BR> }<BR> // Get the variable value...<BR> public int getValue() {<BR> return firstVariable;<BR> }<BR>}</TT></BLOCKQUOTE><P>This class consists of a single variable, called <TT>firstVariable</TT>,which is initially set to <TT>0</TT>.The class has two methods. The <TT>setValue()</TT>method is used to set <TT>firstVariable</TT>to the specified value. The <TT>getValue()</TT>method returns the current value of <TT>firstVariable</TT>.<P>The variable <TT>firstVariable</TT>is called an <I>instance variable</I>. This type of variable isdefined for an instance of an object. It differs from a <I>localvariable</I>, which is defined inside a block of code or a method.Suppose that a new method is defined to get half the value of<TT>firstVariable</TT>:<BLOCKQUOTE><TT>public int getHalf() {<BR> int half; // Alocal variable<BR> half = firstVariable / 2;⌨️ 快捷键说明
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