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All parameterized types share the same interface at runtime. A method is generic if it declares one or more type variables. [8] These type variables are known as the formal type parameters of the method. The form of the formal type parameter list is identical to a type parameter list of a class or interface.
In the Java programming language, the wildcard? is a special kind of type argument [1] that controls the type safety of the use of generic (parameterized) types. [2] It can be used in variable declarations and instantiations as well as in method definitions, but not in the definition of a generic type.
A method has a return value, a name and usually some parameters initialized when it is called with some arguments. Similar to C++, methods returning nothing have return type declared as void. Unlike in C++, methods in Java are not allowed to have default argument values and methods are usually overloaded instead.
In Java, a method signature is composed of a name and the number, type, and order of its parameters. Return types and thrown exceptions are not considered to be a part of the method signature, nor are the names of parameters; they are ignored by the compiler for checking method uniqueness.
In Java, constructors differ from other methods in that: Constructors never have an explicit return type. Constructors cannot be directly invoked (the keyword “new” invokes them). Constructors should not have non-access modifiers. Java constructors perform the following tasks in the following order:
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.
Java, C#, Visual Basic .NET and Delphi have each introduced "generics" for parametric polymorphism. Some implementations of type polymorphism are superficially similar to parametric polymorphism while also introducing ad hoc aspects. One example is C++ template specialization.
There are methods that a subclass cannot override. For example, in Java, a method that is declared final in the super class cannot be overridden. Methods that are declared private or static cannot be overridden either because they are implicitly final. It is also impossible for a class that is declared final to become a super class. [9]