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Primitive wrapper classes are used to create an Object that needs to represent primitive types in Collection classes (i.e., in the Java API), in the java.util package and in the java.lang.reflect reflection package. Collection classes are Java API-defined classes that can store objects in a manner similar to how data structures like arrays ...
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.
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 ...
In Java, having no keyword before defaults to the package-private modifier. When the class is declared as public, it is accessible to other classes defined in the same package as well as those defined in other packages. This is the most commonly used specifier for classes. However, a class itself cannot be declared as private.
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).
Since JDK 1.2, Java has included a standard set of collection classes, the Java collections framework Doug Lea , who also participated in the Java collections framework implementation, developed a concurrency package , comprising several concurrency primitives and a large battery of collection-related classes. [ 19 ]
In the Java computer programming language, an annotation is a form of syntactic metadata that can be added to Java source code. [1] Classes, methods, variables, parameters and Java packages may be annotated. Like Javadoc tags, Java annotations can be read from source files.
An interface in the Java programming language is an abstract type that is used to declare a behavior that classes must implement. They are similar to protocols.Interfaces are declared using the interface keyword, and may only contain method signature and constant declarations (variable declarations that are declared to be both static and final).