Java method argument interface

Package java.util.function

Represents an operation upon two operands of the same type, producing a result of the same type as the operands.

Represents an operation that accepts an object-valued and a double -valued argument, and returns no result.

Represents an operation that accepts an object-valued and a int -valued argument, and returns no result.

Represents an operation that accepts an object-valued and a long -valued argument, and returns no result.

Package java.util.function Description

Functional interfaces provide target types for lambda expressions and method references. Each functional interface has a single abstract method, called the functional method for that functional interface, to which the lambda expression’s parameter and return types are matched or adapted. Functional interfaces can provide a target type in multiple contexts, such as assignment context, method invocation, or cast context:

 // Assignment context Predicate p = String::isEmpty; // Method invocation context stream.filter(e -> e.getSize() > 10). // Cast context stream.map((ToIntFunction) e -> e.getSize()). 

The interfaces in this package are general purpose functional interfaces used by the JDK, and are available to be used by user code as well. While they do not identify a complete set of function shapes to which lambda expressions might be adapted, they provide enough to cover common requirements. Other functional interfaces provided for specific purposes, such as FileFilter , are defined in the packages where they are used.

The interfaces in this package are annotated with FunctionalInterface . This annotation is not a requirement for the compiler to recognize an interface as a functional interface, but merely an aid to capture design intent and enlist the help of the compiler in identifying accidental violations of design intent.

Functional interfaces often represent abstract concepts like functions, actions, or predicates. In documenting functional interfaces, or referring to variables typed as functional interfaces, it is common to refer directly to those abstract concepts, for example using «this function» instead of «the function represented by this object». When an API method is said to accept or return a functional interface in this manner, such as «applies the provided function to. «, this is understood to mean a non-null reference to an object implementing the appropriate functional interface, unless potential nullity is explicitly specified.

• There are several basic function shapes, including Function (unary function from T to R ), Consumer (unary function from T to void ), Predicate (unary function from T to boolean ), and Supplier (nilary function to R ).
• Function shapes have a natural arity based on how they are most commonly used. The basic shapes can be modified by an arity prefix to indicate a different arity, such as BiFunction (binary function from T and U to R ).
• There are additional derived function shapes which extend the basic function shapes, including UnaryOperator (extends Function ) and BinaryOperator (extends BiFunction ).
• Type parameters of functional interfaces can be specialized to primitives with additional type prefixes. To specialize the return type for a type that has both generic return type and generic arguments, we prefix ToXxx , as in ToIntFunction . Otherwise, type arguments are specialized left-to-right, as in DoubleConsumer or ObjIntConsumer . (The type prefix Obj is used to indicate that we don’t want to specialize this parameter, but want to move on to the next parameter, as in ObjIntConsumer .) These schemes can be combined, as in IntToDoubleFunction .
• If there are specialization prefixes for all arguments, the arity prefix may be left out (as in ObjIntConsumer ).

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For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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When to use interface as argument in Java?

In some Java methods I see that an Interface argument is required. Since an Interface cannot be instantiated, does that mean that an object of every class that implements this interface can be passed as argument? For example in the setOnClickListener method of the ListView class in Android,

How to compile Java class to include method parameter names?

We can obtain the names of the parameters of any method or constructor with the method java.lang.reflect.Executable.getParameters (). The classes Method and Constructor extend the class Executable and therefore inherit the method Executable.getParameters ().

What are the parameters of the command line in Java?

Command line arguments (parameters) are strings of text used to pass additional information to a program when an application is run through the command line interface (CLI) of an operating system. In this tutorial, we’ll be accessing the arguments (parameters) passed into the main method of a Java application and reading them.

How to access arguments in Java command line?

Alternatively, Java also supports a vararg in this place: That being said, we can easily access each argument passed into this method. Let’s start out by printing them out, one by one: We’ll then compile this .java file: After which, we can run it: The arguments themselves are an array of Strings.

Which is the list interface class in Java?

ArrayList: ArrayList class which is implemented in the collection framework provides us dynamic arrays in Java. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in the array is needed. Let’s see how to create a list object using this class.

Can a method receive an argument in Java?

In Java, is it possible to define an interface that has a method that receives an argument of the implementing class? public class A implements MyInterface < public void method (A object) < >> What I want to avoid is that a class could implement MyInterface with another class like itself. So this should not be allowed:

How to define a functional interface in Java?

1 A functional interface has only one abstract method but it can have multiple default methods. 2 @FunctionalInterface annotation is used to ensure an interface can’t have more than one abstract method. The use of this annotation is optional. 3 The java.util.function package contains many builtin functional interfaces in Java 8.

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Pass Method as a Parameter in Java 8

In this tutorial, you are going to learn ‘how to pass method as a parameter in Java’ . and to do that, we are going to use unique concepts introduced in Java 8 and sample codes are provided below to help you understand better.

Before Java 8, there were no such thing as passing method as an argument but Java 8 introduced Lambda Expressions and Method References which can be used to pass as an argument. All thanks to the concept of OOPS and its support of functional style of writing code.

Pass Method as a Parameter using Lambda Function

In this example, we are iterating an ArrayList and then printing each value of the list. It’s a very simple example where we are passing the Lambda function to the forEach() method. This lambda function is just taking the argument and printing it using sysout.

List listOfStudents = Arrays . asList ( «Sam» , «Henry» , «Yash» , «Yashika» , «Donna» , «Victoria» , «John» , «Jenny» ) ;

listOfStudents . forEach ( x — > System . out . println ( x ) ) ; //Passing Lambda Function as an argument to another function >

Output:

Pass Method as a Parameter using Consumer Interface

In this example, we are iterating an Array List and printing the values which starts with character ‘J’. Java 8 introduced Functional interfaces and in that, one is Consumer Interface. CI takes one input argument and return no result. and the interesting thing is that Lambda expressions can be stored in variable as long as the variable’s type is an interface which has only one method and this perfectly suits to Consumer Interface.

Therefore, in the below example, we are creating a lambda expression and then storing it into a Consumer interface variable and then supplying it to forEach() method. If you are thinking why we are using consumer interface is because the list’s forEach() method takes consumer interface as its parameter. Look at the below example:

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