Creating and Using Packages创建和使用包

To make types easier to find and use, to avoid naming conflicts, and to control access, programmers bundle groups of related types into packages.为了使类型更易于查找和使用，避免命名冲突，并控制访问，程序员将相关类型的组捆绑到包中。

The types that are part of the Java platform are members of various packages that bundle classes by function: fundamental classes are in java.lang, classes for reading and writing (input and output) are in java.io, and so on. 作为Java平台一部分的类型是按函数捆绑类的各种包的成员：基本类在Java.lang中，用于读写（输入和输出）的类在Java.io中，等等。You can put your types in packages too.您也可以将类型放入包中。

Suppose you write a group of classes that represent graphic objects, such as circles, rectangles, lines, and points. 假设您编写了一组表示图形对象的类，例如圆、矩形、直线和点。You also write an interface, Draggable, that classes implement if they can be dragged with the mouse.您还编写了一个接口Dragable，如果可以用鼠标拖动类，则类将实现该接口。

//in the Draggable.java file
public interface Draggable {
    ...
}

//in the Graphic.java file
public abstract class Graphic {
    ...
}

//in the Circle.java file
public class Circle extends Graphic
    implements Draggable {
    . . .
}

//in the Rectangle.java file
public class Rectangle extends Graphic
    implements Draggable {
    . . .
}

//in the Point.java file
public class Point extends Graphic
    implements Draggable {
    . . .
}

//in the Line.java file
public class Line extends Graphic
    implements Draggable {
    . . .
}

You should bundle these classes and the interface in a package for several reasons, including the following:出于以下几个原因，您应该将这些类和接口捆绑在一个包中：

• You and other programmers can easily determine that these types are related.您和其他程序员可以很容易地确定这些类型是相关的。
• You and other programmers know where to find types that can provide graphics-related functions.您和其他程序员知道在哪里可以找到可以提供图形相关函数的类型。
• The names of your types won't conflict with the type names in other packages because the package creates a new namespace.类型的名称不会与其他包中的类型名称冲突，因为包会创建一个新的命名空间。
• You can allow types within the package to have unrestricted access to one another yet still restrict access for types outside the package.您可以允许包内的类型不受限制地相互访问，但仍可以限制对包外类型的访问。