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If a package declaration is not used, classes are placed in an unnamed package. Classes in an unnamed package cannot be imported by classes in any other package. [3] The official Java Tutorial advises against this: Generally speaking, an unnamed package is only for small or temporary applications or when you are just beginning the development ...
An object that applies this pattern can provide the equivalent of a namespace, providing the initialization and finalization process of a static class or a class with static members with cleaner, more concise syntax and semantics. It supports specific cases where a class or object can be considered structured, procedural data.
The java.io package contains classes that support input and output. The classes in the package are primarily stream-oriented; however, a class for random access files is also provided. The central classes in the package are InputStream and OutputStream, which are abstract base classes for reading from and writing to byte streams, respectively
Code from other packages is accessed by prefixing the package name before the appropriate identifier, for example class String in package java.lang can be referred to as java.lang.String (this is known as the fully qualified class name). Like C++, Java offers a construct that makes it unnecessary to type the package name (import).
The Java Module System does not intend to support all the functionalities that the OSGi platform currently supports (for example the Life-Cycle model and the Services Registry). However the Java Module System will support functions which are not supported by OSGi, such as modularity at compile-time, and built-in support for native libraries. [15]
The term assembly (as in .NET languages like C#, F# or Visual Basic .NET) or package (as in Dart, Go or Java) is sometimes used instead of module.In other implementations, these are distinct concepts; in Python a package is a collection of modules, while in Java 9 the introduction of the new module concept (a collection of packages with enhanced access control) was implemented.
Packages are a part of a class name and they are used to group and/or distinguish named entities from other ones. Another purpose of packages is to govern code access together with access modifiers. For example, java.io.InputStream is a fully qualified class name for the class InputStream which is located in the package java.io.
The java.lang.Class [2] class is the basis of more advanced introspection. For instance, if it is desirable to determine the actual class of an object (rather than whether it is a member of a particular class), Object.getClass() and Class.getName() can be used: