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 陈杨 /@RunWith(SpringRunner.class)@SpringBootTestpublic class FuncInterface {一、函数式编程的理解// 函数式编程的理解//// 函数接口式编程 是 对 业务应用的进一步抽象// 在类方法定义中 只需实现FunctionalInterface 而不管业务实现的逻辑// 在外部应用 调用该业务时 使用Lambda表达式 灵活实现其业务逻辑二、 函数式接口的测试方法1、Function接口// FunctionFunction<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接口// BiFunctionBiFunction<Integer, Integer, Integer> subtract = (first, last) -> first - last;public int testBiFunctionAndThen(Integer first, Integer last) { return subtract.andThen(multiply).apply(first, last);}3、BinaryOperator接口// BinaryOperatorBinaryOperator<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);}//比较器//比较字符串的长度Comparator<String> length = (first, last) -> first.length() - last.length();//比较字符串首字母ASCII码大小Comparator<String> asc = (first, last) -> first.charAt(0) - last.charAt(0);4、Predicate接口// Predicatepublic 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接口// Supplier@Data@AllArgsConstructor@NoArgsConstructorprivate class Student { private Integer id; private String name; private String sex; private Integer age; private String addr; private Double salary;}三、测试结果 . ____ _ __ _ _ /\ / ’ __ _ () __ __ _ \ \ \ ( ( )__ | ‘_ | ‘| | ‘ / ` | \ \ \ \ \/ )| |)| | | | | || (| | ) ) ) ) ’ || .__|| ||| |_, | / / / / =========||==============|/=//// :: 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: default2019-01-31 11:51:58.988 INFO 12080 — [ main] com.java.design.java8.FuncInterface : Started FuncInterface in 0.729 seconds (JVM running for 1.556)——————–Function接口的理解———————6581——————BiFunction接口的理解———————64——————-Predicate接口的理解———————获取满足条件的集合：大于4[5, 6, 7, 8, 9]——————————获取满足条件的集合：大于4且是偶数[6, 8]——————————获取满足条件的集合：大于4 取反[1, 2, 3, 4, 0]——————————获取满足条件的集合：大于4或是偶数[2, 4, 5, 6, 7, 8, 9, 0]——————————使用Objects的Equals方法判断对象是否相同true——————————Predicate.not()返回(Predicate<T>)target.negate(); [1, 2, 3, 4, 0]——————————双重否定表肯定[5, 6, 7, 8, 9]————————————————-Supplier接口的理解———————FuncInterface.Student(id=1, name=Kirito, sex=Male, age=18, addr=ShenZhen, salary=9.99999999E8)———————————————BinaryOperator接口的理解——————-继承BiFunction的Apply方法 实现减法10 - 2 = 8——————————字符串较短的是：Asuna字符串较长的是：Kirito——————————字符串首字母ASCII码较小的是：Asuna字符串首字母ASCII码较大的是：KiritoProcess finished with exit code 0四、透过现象看本质 函数式接口的源码实现1、Function接口@Testpublic void testFuncInterface() { System.out.println("——————–Function接口的理解———————\n"); // Function接口的理解 // public interface Function<T, R> // R apply(T t); // Represents a function that accepts one argument and produces a result. // 一个函数：接收一个参数 返回一个结果 // T 输入类型 R 输出类型 /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. / // 输入–>beforeFunction()处理–>得到结果作为下一个函数apply()的输入参数 形成函数式接口的串联调用 // beforeFunction 在当前函数apply前 进行调用 /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. / // 输入–>apply()处理–>得到结果作为下一个函数after.apply()的输入参数 形成函数式接口的串联调用 // afterFunction 在当前函数apply后 进行调用 /static <T> Function<T, T> identity() { return t -> t; * Returns a function that always returns its input argument. }/ // 总是返回输入参数 // 总结： // function1.compose(function2) 执行顺序 –>BeforeFunction()–>thisFunction()–> function2 –> function1 // function1.andThen(function2) 执行顺序 –>thisFunction()–>AfterFunction()–> function1 –> function2 // 前一个函数的运算结果 作为下一个函数的输入参数 // 理解运行时机 可以类比 Junit中 @Before 与 @After System.out.println(this.testFunctionCompose(8)); System.out.println(this.testFunctionAndThen(8));2、BiFunction接口System.out.println("——————BiFunction接口的理解———————\n");// BiFunction 接口 的 理解// @FunctionalInterface// public interface BiFunction<T, U, R> {// R apply(T t, U u);// 一个函数：接收二个参数 返回一个结果/ 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)); } }/// 利用反证法 可以证明 BiFunction 没有 compose方法 (提示： 参数 与 返回值)// 将2个参数应用于BiFunction 只会得到一个返回值 这个返回值会作为Function传入的参数// biFunction.andthen(function)System.out.println(this.testBiFunctionAndThen(10, 2));3、Predicate接口System.out.println("——————-Predicate接口的理解———————\n");// public interface Predicate<T> {// Represents a predicate (boolean-valued function) of one argument./ * Evaluates this predicate on the given argument. * * 接收一个判断 判断是否满足预期条件 返回true false * boolean test(T t); /System.out.println(“获取满足条件的集合：大于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. * * 短路逻辑与计算 * default Predicate<T> and(Predicate<? super T> other) { * Objects.requireNonNull(other); * return (t) -> test(t) && other.test(t); }/System.out.println(“获取满足条件的集合：大于4且是偶数”);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. * * 取反 * default Predicate<T> negate() { * return (t) -> !test(t); * } /System.out.println(“获取满足条件的集合：大于4 取反”);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. * * 短路逻辑或计算 * default Predicate<T> or(Predicate<? super T> other) { * Objects.requireNonNull(other); * return (t) -> test(t) || other.test(t); * } /System.out.println(“获取满足条件的集合：大于4或是偶数”);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)}. * * 根据Objects的equals方法 来判断两个对象 是否相同 * static <T> Predicate<T> isEqual(Object targetRef) { * return (null == targetRef) * ? Objects::isNull * : object -> targetRef.equals(object); * } /System.out.println(“使用Objects的Equals方法判断对象是否相同”);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()}. * * 返回提供的predicate的否定 * @SuppressWarnings(“unchecked”) * static <T> Predicate<T> not(Predicate<? super T> target) { * Objects.requireNonNull(target); * return (Predicate<T>)target.negate(); * } * } /System.out.println(“Predicate.not()返回(Predicate<T>)target.negate(); “);System.out.println(testPredicate(this.notPredicate(integer -> integer > 4)));System.out.println(”——————————\n”);System.out.println(“双重否定表肯定”);System.out.println(testPredicateNegate(this.notPredicate(integer -> integer > 4)));System.out.println("——————————\n");4、Supplier接口System.out.println("——————-Supplier接口的理解———————\n");/ * Represents a supplier of results. * * public interface Supplier<T> { * T get(); * } /// 构造方法引用 构造函数接口实例// 利用Supplier接口 Student类必须要有无参的构造方法// 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接口 System.out.println("—————BinaryOperator接口的理解——————-\n"); / * * public interface BinaryOperator<T> extends BiFunction<T,T,T> { * * 返回2个比较参数之间的较小值 * public static <T> BinaryOperator<T> minBy(Comparator<? super T> comparator) { * Objects.requireNonNull(comparator); * return (a, b) -> comparator.compare(a, b) <= 0 ? a : b; * } * * 返回2个比较参数之间的较大值 * 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(“继承BiFunction的Apply方法 实现减法”); System.out.println(“10 - 2 = “+this.testBinaryOperator(10, 2)); System.out.println(”——————————\n”); System.out.println(“字符串较短的是："+this.testMinBy(“Kirito”,“Asuna”,length)); System.out.println(“字符串较长的是："+this.testMaxBy(“Kirito”,“Asuna”,length)); System.out.println(”——————————\n”); System.out.println(“字符串首字母ASCII码较小的是："+this.testMinBy(“Kirito”,“Asuna”,asc)); System.out.println(“字符串首字母ASCII码较大的是："+this.testMaxBy(“Kirito”,“Asuna”,asc)); }}
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