1、,2,Package:the Library Unit,import java.util.*; import java.util.Vector; Managing “name spaces” Class members are already hidden inside class Class names could clash Need completely unique name even over the Internet Compilation units (.java files) Name of .java file = name of single public class Ot

2、her non-public classes are not visible Each class in file gets its own .class file Program is a bunch of .class files (no .obj or .lib),3,Creating a Library of Classes,package mypackage; public class is under the umbrella mypackage Client programmer must import mypackage.*; Creating unique package n

3、ames Location on disk encoded into package name Convention: first part of package name is Internet domain name of class creator (reversed) Java interpreter uses CLASSPATH environment variable as starting point for search My domain: package com.bruceeckel.util; (Note change to lowercase com),4,A Simp

4、le Library,package com.bruceeckel.util; public class Vector public Vector() System.out.println(com.bruceeckel.util.Vector); / package com.bruceeckel.util; / Separate file public class List public List() System.out.println(com.bruceeckel.util.List); ,5,Library Location,C:DOCJavaTcombruceeckelutil CLA

5、SSPATH takes care of first part: CLASSPATH=.;D:JAVALIB;C:DOCJavaT Programs can be in any directory,6,Library Location,import com.bruceeckel.util.*; public class LibTest public static void main(String args) Vector v = new Vector(); List l = new List(); Compiler starts search at CLASSPATH (Java 2 has

6、improved things),7,目錄、包、類的關(guān)系,d1,d2,p1,p2,p3,類,包,Classpath= d:d1;d:d1d2,8,9,“Friendly”,Default access, has no keyword public to other members of the same package, private to anyone outside the package Easy interaction for related classes (that you place in the same package) Also referred to as “packa

7、ge access”,10,public: Interface Access,package c05.dessert; public class Cookie public Cookie() System.out.println(Cookie constructor); void foo() System.out.println(foo); / Separate file in separate package: import c05.dessert.*; public class Dinner public Dinner() System.out.println(Dinner constru

8、ctor); public static void main(String args) Cookie x = new Cookie(); /! x.foo(); / Cant access ,11,private: Cant Touch That!,class Sundae private Sundae() static Sundae makeASundae() return new Sundae(); public class IceCream public static void main(String args) /! Sundae x = new Sundae(); Sundae x

9、= Sundae.makeASundae(); ,12,protected,Finer grained, deals with inheritance Generally: when you need it, youll know Covered in book; well see it later,13,類成員的訪問(wèn)修飾符與訪問(wèn)能力之間的關(guān)系,14,Class Access,Classes as a whole can be public or “friendly” Only one public class per file, usable outside the package All other classes “friendly,” only usable within the package,15,Summary,Access control tells users what they can & cant use (shows the area of interest) Also separates interface & implementation Allows the class creator to change the implementat