Package
- PROGRAMS are organized as sets of packages. Each has its own set of
names for types, which helps to prevent name conflicts. - A top level type is accessible outside thepackagethat declares
it only if the type is declared public. - The naming structure for packages is hierarchical . The members of a
package are class and interface types , which are declared in compilation
units of the package, and subpackages, which may contain compilation units and
subpackages of their own. - A package can be stored in a file system or in a database .
- Packages that are stored in a file system may have certain constraints on the organization of their compilation units to allow a simple implementation to find
classes easily. - A package consists of a number of compilation units .
- A compilation
unit automatically has access to all types declared in its package and also automatically imports all of the public types declared in the
predefined package
java.lang.
- For small programs and casual development, a package can be unnamed
or have a simple name, but if code is to be widely distributed, unique
package names should be chosen . - This can prevent the conflicts that would
otherwise occur if two development groups happened to pick the same package
name and these packages were later to be used in a single program.
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