functional interface java

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Innocent Iguana answered on May 5, 2021 Popularity 10/10 Helpfulness 2/10

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import java.util.function.Function;

public class FunctionalProgrammingExample {

    public static void main(String[] args) {
        // Functional interfaces are interfaces designed for a single function and provide ways for specific functional behaviors
        //  Example 1 : Consumer functional interface  (a void function, to be fair)

        Consumer<String> myConsumer = (message) -> {System.out.println("Consumer: " + message)}; //Takes input as String, produces no output
        myConsumer.accept("Hello, Consumer!"); // Calling the consumer


        // Example 2 : Runable concurrent functional interface  
        Runnable myRunnable = () -> {
            for (int i = 0; i < 5; i++) {
                System.out.println("Runnable: " + i);
                }
            };
        Thread myThread = new Thread(myRunnable);
        myThread.start(); // calling the runnable

        // Example 3 : Chaining functional interfaces
        
        Function<Integer, Integer> first = x -> x + 2; // Takes input as Integers, generates output as Integers
        Function<Integer, Integer> second = x -> x * 3; // Takes input as Integers, generates output as Integers
        
        // valid as long as the first functions output can be accepted as the second function's input
      	// Also valid for method reference in .andThen
        Function<Integer, Integer> firstThenSecond = first.andThen(second); // Using andThen to compose a pipeline of functions 
        int result = firstThenSecond.apply(5); // Calling the composed function
      	first.andThen(System.out::println);// Calling with method reference
    }
}

Popularity 10/10 Helpfulness 2/10 Language java

Source: Grepper

Tags: functional-interface java

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Contributed on Jan 01 2024

Innocent Iguana

0 Answers Avg Quality 2/10

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interface java

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//Since Java9, Interface now has methods: 
//public abstract, public default, public static, private, private static
//default methods have body (implementation), is inherited by subclasses. 
//static methods is the same as regular static methods.
//private methods and private static methods are helper methods.

public interface CustomInterface {
    public abstract void method1();
    public default void method2() {
        method4();  //private method inside default method
        method5();  //static method inside other non-static method
        System.out.println("default method");
    }
    public static void method3() {
        method5(); //static method inside other static method
        System.out.println("static method");
    }
    private void method4(){
        System.out.println("private method");
    } 
    private static void method5(){
        System.out.println("private static method");
    } 
}
 
public class CustomClass implements CustomInterface {
    @Override
    public void method1() {
        System.out.println("abstract method");
    }
    public static void main(String[] args){
        CustomInterface instance = new CustomClass();
        instance.method1();
        instance.method2();
        CustomInterface.method3();
    }
}

/* Output:
abstract method
private method
private static method
default method
private static method
static method
*/

// Another example of default and private methods
import java.util.function.IntPredicate;
import java.util.stream.IntStream;
 
public interface CustomCalculator 
{
    default int addEvenNumbers(int... nums) {
        return add(n -> n % 2 == 0, nums);
    }
    default int addOddNumbers(int... nums) {
        return add(n -> n % 2 != 0, nums);
    }
    private int add(IntPredicate predicate, int... nums) { 
        return IntStream.of(nums)
                .filter(predicate)
                .sum();
    }
}

public class Main implements CustomCalculator {
     public static void main(String[] args) {
        CustomCalculator demo = new Main();
         
        int sumOfEvens = demo.addEvenNumbers(1,2,3,4,5,6,7,8,9);
        System.out.println(sumOfEvens);
         
        int sumOfOdds = demo.addOddNumbers(1,2,3,4,5,6,7,8,9);
        System.out.println(sumOfOdds);
    } 
}
/* output:
20
25
*/

Popularity 10/10 Helpfulness 3/10 Language java

Source: howtodoinjava.com

Tags: default-method defa

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Contributed on Sep 19 2022

Grotesque Gibbon

0 Answers Avg Quality 2/10

interface java

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public interface SomeInterface{
	default void test(){
    	//this will be done when the method is called by default
    }
	public void newTest();
}
public interface OtherInterface extends SomeInterface{
	// test() is available
    // newTest() is available
	public void otherTest();
}
public class SomeInterfaceImpl implements SomeInterface{
	//has test method from SomeInterface, can be overwritten
	@Override
	public void newTest() {
		// must override the non-default method
	}
}
public class SomeClass{
	public void test(){
    	//do something else
    }
}
public class SomeOtherClass extends SomeClass implements OtherInterface{
	//uses the test method from SomeClass instead of SomeInterface
	@Override
	public void newTest() {
		// must override the non-default method inherited in OtherInterface
	}
	public void otherTest() {
		// must override the non-default new method in OtherInterface
	}
}

Popularity 9/10 Helpfulness 2/10 Language java

Source: Grepper

Tags: interface inte

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Contributed on Dec 11 2023

Innocent Iguana

0 Answers Avg Quality 2/10

functional interface java

Comment

A functional interface is an interface that contains only one abstract method. They can have only one functionality to exhibit.

Popularity 10/10 Helpfulness 2/10 Language java

Source: Grepper

Tags: functional-interface functional-inter

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Contributed on May 05 2021

oubaydos

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Java Interface

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// interface
interface Animal {
  public void animalSound(); // interface method (does not have a body)
  public void run(); // interface method (does not have a body)
}

Popularity 10/10 Helpfulness 2/10 Language java

Source: Grepper

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Contributed on May 23 2022

naly moslih

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Interface declaration in java

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Public abstract interface Multi{ //Interface declaration
Public abstract void multi();//method declaration
public abstract void subtract();
}

Popularity 10/10 Helpfulness 2/10 Language java

Source: softhunt.net

Tags: declaration decl

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Contributed on May 10 2022

Outrageous Ostrich

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interface in java

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An interface can contain:

public constants;
abstract methods without an implementation (the keyword abstract is not required here);
default methods with implementation (the keyword default is required);
static methods with implementation (the keyword static is required);
private methods with implementation.
Java 9 onwards, you can include private methods in interfaces. Before Java 9 
it was not possible.
An interface can't contain fields (only constants), constructors,
 or non-public abstract methods.
The keyword abstract before a method means that the method does not have a
body, it just declares a signature.

Popularity 10/10 Helpfulness 1/10 Language java

Source: Grepper

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Contributed on Jan 28 2022

coder

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interface in java

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In many cases, it is more important to know what an object can do,instead of 
how it does what it does. This is a reason why interfaces are commonly used for
declaring a type of variable.
 interface : DrawingTool : a tool can draw
 interface DrawingTool {
    void draw(Curve curve);
}
DrawingTool pencil = new Pencil();
DrawingTool brush = new Brush();
Both Pencil and brush class should implement draw method

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Contributed on Jan 28 2022

coder

0 Answers Avg Quality 2/10

Interface in java

Comment

public interface Shape {
    void draw(); // Abstract method
    double area(); // Abstract method
}

Popularity 9/10 Helpfulness 1/10 Language java

Source: Grepper

Tags: interface inte

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Contributed on Dec 24 2023

sam9934

0 Answers Avg Quality 2/10

interface in java

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interface Interface {
        
    int INT_CONSTANT = 0; // it's a constant, the same as public static final int INT_FIELD = 0
        
    void instanceMethod1();
        
    void instanceMethod2();
        
    static void staticMethod() {
        System.out.println("Interface: static method");
    }
        
    default void defaultMethod() {
        System.out.println("Interface: default method. It can be overridden");
    }

    private void privateMethod() {
        System.out.println("Interface: private methods in interfaces are acceptable but should have a body");
    }
}
Static, default, and private methods should have an implementation in the interface!

Popularity 10/10 Helpfulness 1/10 Language java

Source: Grepper

Tags: interface inte

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Contributed on Jan 28 2022

coder

0 Answers Avg Quality 2/10

functional interface java

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