package com.java.design.java8;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.function.*;
import java.util.stream.Collectors;
/**
* @author Chen Yang
*/
@RunWith(SpringRunner.class)
@SpringBootTest
public class FuncInterface {I. understanding of functional programming
//Understanding of functional programming // //Functional interface programming is a further abstraction of business applications //In the class method definition, only functional interface needs to be implemented regardless of the logic of business implementation //Using Lambda expression to flexibly implement the business logic when the external application calls the business
II. Test method of functional interface
1. Function interface
// Function
Function<Integer, Integer> sum = integer -> integer + 1;
Function<Integer, Integer> multiply = integer -> integer * integer;
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 0);
public int testFunctionCompose(Integer integer) {
return sum.compose(multiply).apply(integer);
}
public int testFunctionAndThen(Integer integer) {
return sum.andThen(multiply).apply(integer);
}2. BiFunction interface
// BiFunction
BiFunction<Integer, Integer, Integer> subtract = (first, last) -> first - last;
public int testBiFunctionAndThen(Integer first, Integer last) {
return subtract.andThen(multiply).apply(first, last);
}3. BinaryOperator interface
// BinaryOperator
BinaryOperator<Integer> binaryOperator = (first, last) -> first - last;
public int testBinaryOperator(Integer first, Integer last) {
return binaryOperator.apply(first, last);
}
public String testMinBy(String first, String last, Comparator<String> comparator) {
return BinaryOperator.minBy(comparator).apply(first, last);
}
public String testMaxBy(String first, String last, Comparator<String> comparator) {
return BinaryOperator.maxBy(comparator).apply(first, last);
}//comparator //Compare the length of a string Comparator<String> length = (first, last) -> first.length() - last.length(); //Compare string initial ASCII size Comparator<String> asc = (first, last) -> first.charAt(0) - last.charAt(0);
4. Predict interface
// Predicate
public List<Integer> testPredicate(Predicate<Integer> predicate) {
return list.stream().filter(predicate).collect(Collectors.toList());
}
public Predicate<String> isEqual(Object object) {
return Predicate.isEqual(object);
}
public Predicate<Integer> notPredicate(Predicate<Integer> predicate) {
return Predicate.not(predicate);
}
public List<Integer> testPredicateNegate(Predicate<Integer> predicate) {
return list.stream().filter(predicate.negate()).collect(Collectors.toList());
}
public List<Integer> testPredicateAnd(Predicate<Integer> first, Predicate<Integer> last) {
return list.stream().filter(first.and(last)).collect(Collectors.toList());
}
public List<Integer> testPredicateOr(Predicate<Integer> first, Predicate<Integer> last) {
return list.stream().filter(first.or(last)).collect(Collectors.toList());
}5. Supplier interface
// Supplier
@Data
@AllArgsConstructor
@NoArgsConstructor
private class Student {
private Integer id;
private String name;
private String sex;
private Integer age;
private String addr;
private Double salary;
}III. test results
. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.1.2.RELEASE) 2019-01-31 11:51:58.460 INFO 12080 --- [ main] com.java.design.java8.FuncInterface : Starting FuncInterface on DESKTOP-87RMBG4 with PID 12080 (started by 46250 in E:\IdeaProjects\design) 2019-01-31 11:51:58.461 INFO 12080 --- [ main] com.java.design.java8.FuncInterface : No active profile set, falling back to default profiles: default 2019-01-31 11:51:58.988 INFO 12080 --- [ main] com.java.design.java8.FuncInterface : Started FuncInterface in 0.729 seconds (JVM running for 1.556) --------------------Understanding of Function interface--------------------- 65 81 ------------------Understanding of BiFunction interface--------------------- 64 -------------------Understanding of predict interface--------------------- Get a set that meets the criteria: greater than 4 [5, 6, 7, 8, 9] ------------------------------ Get the set satisfying the condition: greater than 4 and even [6, 8] ------------------------------ Get the set that meets the conditions: more than 4 negates [1, 2, 3, 4, 0] ------------------------------ Get the set that meets the condition: greater than 4 or even [2, 4, 5, 6, 7, 8, 9, 0] ------------------------------ Use the Equals method of Objects to determine whether the Objects are the same true ------------------------------ Predict. Not() returns (predict < T >) target. Gate(); [1, 2, 3, 4, 0] ------------------------------ Double negation for affirmation [5, 6, 7, 8, 9] ------------------------------ -------------------Understanding of Supplier interface--------------------- FuncInterface.Student(id=1, name=Kirito, sex=Male, age=18, addr=ShenZhen, salary=9.99999999E8) ------------------------------ ---------------Understanding of the BinaryOperator interface------------------- Implementation of subtraction by applying method inheriting BiFunction 10 - 2 = 8 ------------------------------ The short string is: Asuna The long string is: Kirito ------------------------------ String initial ASCII is smaller: Asuna The big one is: Kirito Process finished with exit code 0
4. See the source code implementation of the essential function interface through the phenomenon
1. Function interface
@Test
public void testFuncInterface() {
System.out.println("--------------------Function Interface understanding---------------------\n");
// Understanding of Function interface
// public interface Function<T, R>
// R apply(T t);
// Represents a function that accepts one argument and produces a result.
// A function: receive a parameter and return a result
// T input type R output type
/*default <V> Function<V, R> compose(Function<? super V, ? extends T> before) {
Objects.requireNonNull(before);
return (V v) -> apply(before.apply(v));
}
* Returns a composed function that first applies the {@code before}
* function to its input, and then applies this function to the result.
* If evaluation of either function throws an exception, it is relayed to
* the caller of the composed function.
*/
// Input -- > beforefunction() processing -- > the result is used as the input parameter of the next function apply() to form a series call of the functional interface
// beforeFunction is called before the current function is applied
/*default <V> Function<T, V> andThen(Function<? super R, ? extends V> after) {
Objects.requireNonNull(after);
return (T t) -> after.apply(apply(t));
}
* Returns a composed function that first applies this function to
* its input, and then applies the {@code after} function to the result.
* If evaluation of either function throws an exception, it is relayed to
* the caller of the composed function.
*/
// Input -- > apply() process -- > get the result as the input parameter of the next function after.apply() to form a series call of the functional interface
// afterFunction is called after the current function is applied
/*static <T> Function<T, T> identity() {
return t -> t;
* Returns a function that always returns its input argument.
}*/
// Always return input parameters
// Conclusion:
// Function 1. Compose (function2) execution order -- > beforefunction() --- > thisfunction() --- function2 -- > function1
// function1.andThen(function2) execution order -- > thisfunction() --- > afterfunction() --- function1 -- > function2
// The operation result of the previous function is the input parameter of the next function
// To understand the operation time, you can compare @ Before and @ After in Junit
System.out.println(this.testFunctionCompose(8));
System.out.println(this.testFunctionAndThen(8));2. BiFunction interface
System.out.println("------------------BiFunction Interface understanding---------------------\n");
// Understanding of BiFunction interface
// @FunctionalInterface
// public interface BiFunction<T, U, R> {
// R apply(T t, U u);
// A function: receive two parameters and return a result
/*
default <V> BiFunction<T, U, V> andThen(Function<? super R, ? extends V> after) {
Objects.requireNonNull(after);
return (T t, U u) -> after.apply(apply(t, u));
}
}
*/
// It can be proved that BiFunction does not have the compose method by using the counter evidence method (hint: parameters and return values)
// Applying two parameters to BiFunction will only get one return value, which will be the parameter passed in as Function
// biFunction.andthen(function)
System.out.println(this.testBiFunctionAndThen(10, 2));3. Predict interface
System.out.println("-------------------Predicate Interface understanding---------------------\n");
// public interface Predicate<T> {
// Represents a predicate (boolean-valued function) of one argument.
/*
* Evaluates this predicate on the given argument.
*
* Receive a judgment to determine whether the expected condition is met and return true false
* boolean test(T t);
*/
System.out.println("Get a set that meets the criteria: greater than 4");
System.out.println(this.testPredicate(in -> in > 4));
System.out.println("------------------------------\n");
/*
* Returns a composed predicate that represents a short-circuiting logical
* AND of this predicate and another. When evaluating the composed
* predicate, if this predicate is {@code false}, then the {@code other}
* predicate is not evaluated.
*
* Short circuit logic and calculation
* default Predicate<T> and(Predicate<? super T> other) {
* Objects.requireNonNull(other);
* return (t) -> test(t) && other.test(t);
}*/
System.out.println("Get the set satisfying the condition: greater than 4 and even");
System.out.println(this.testPredicateAnd(in -> in > 4, in -> in % 2 == 0));
System.out.println("------------------------------\n");
/*
* Returns a predicate that represents the logical negation of this
* predicate.
*
* Take inverse
* default Predicate<T> negate() {
* return (t) -> !test(t);
* }
*/
System.out.println("Get the set that meets the conditions: more than 4 negates");
System.out.println(this.testPredicateNegate(in -> in > 4));
System.out.println("------------------------------\n");
/*
* Returns a composed predicate that represents a short-circuiting logical
* OR of this predicate and another. When evaluating the composed
* predicate, if this predicate is {@code true}, then the {@code other}
* predicate is not evaluated.
*
* Short circuit logic or calculation
* default Predicate<T> or(Predicate<? super T> other) {
* Objects.requireNonNull(other);
* return (t) -> test(t) || other.test(t);
* }
*/
System.out.println("Get the set that meets the condition: greater than 4 or even");
System.out.println(this.testPredicateOr(in -> in > 4, in -> in % 2 == 0));
System.out.println("------------------------------\n");
/*
* Returns a predicate that tests if two arguments are equal according
* to {@link Objects#equals(Object, Object)}.
*
* Judge whether two Objects are the same according to the equals method of Objects
* static <T> Predicate<T> isEqual(Object targetRef) {
* return (null == targetRef)
* ? Objects::isNull
* : object -> targetRef.equals(object);
* }
*/
System.out.println("Use Objects Of Equals Method to judge whether the objects are the same");
System.out.println(this.isEqual("Kirito").test("Kirito"));
System.out.println("------------------------------\n");
/*
* Returns a predicate that is the negation of the supplied predicate.
* This is accomplished by returning result of the calling
* {@code target.negate()}.
*
* Returns the negation of the supplied predicate
* @SuppressWarnings("unchecked")
* static <T> Predicate<T> not(Predicate<? super T> target) {
* Objects.requireNonNull(target);
* return (Predicate<T>)target.negate();
* }
* }
*/
System.out.println("Predicate.not()Return(Predicate<T>)target.negate(); ");
System.out.println(testPredicate(this.notPredicate(integer -> integer > 4)));
System.out.println("------------------------------\n");
System.out.println("Double negation for affirmation");
System.out.println(testPredicateNegate(this.notPredicate(integer -> integer > 4)));
System.out.println("------------------------------\n");4. Supplier interface
System.out.println("-------------------Supplier Interface understanding---------------------\n");
/*
* Represents a supplier of results.
*
* public interface Supplier<T> {
* T get();
* }
*/
// Constructor reference constructor interface instance
// Using the Supplier interface Student class must have a construction method with or without parameters
// Supplier<Student> studentSupplier = () -> new Student();
Supplier<Student> studentSupplier = Student::new;
Student student = studentSupplier.get();
student.setId(1);
student.setName("Kirito");
student.setSex("Male");
student.setAge(18);
student.setSalary(999999999.0);
student.setAddr("ShenZhen");
System.out.println(student);
System.out.println("------------------------------\n");5. BinaryOperator interface
System.out.println("---------------BinaryOperator Interface understanding-------------------\n");
/*
*
* public interface BinaryOperator<T> extends BiFunction<T,T,T> {
*
* Returns the smaller value between the two comparison parameters
* public static <T> BinaryOperator<T> minBy(Comparator<? super T> comparator) {
* Objects.requireNonNull(comparator);
* return (a, b) -> comparator.compare(a, b) <= 0 ? a : b;
* }
*
* Returns the larger value between the two comparison parameters
* public static <T> BinaryOperator<T> maxBy(Comparator<? super T> comparator) {
* Objects.requireNonNull(comparator);
* return (a, b) -> comparator.compare(a, b) >= 0 ? a : b;
* }
* }
*/
System.out.println("inherit BiFunction Of Apply Method implementation subtraction");
System.out.println("10 - 2 = "+this.testBinaryOperator(10, 2));
System.out.println("------------------------------\n");
System.out.println("The shorter string is:"+this.testMinBy("Kirito","Asuna",length));
System.out.println("The long string is:"+this.testMaxBy("Kirito","Asuna",length));
System.out.println("------------------------------\n");
System.out.println("String initial ASCII The smaller ones are:"+this.testMinBy("Kirito","Asuna",asc));
System.out.println("String initial ASCII The larger one is:"+this.testMaxBy("Kirito","Asuna",asc));
}
}