Java-8-UnaryOperator

Java-8-UnaryOperator

UnaryOperator extends Function<T, T>

源码:

@FunctionalInterface
public interface UnaryOperator<T> extends Function<T, T> {

    
    static <T> UnaryOperator<T> identity() {
        return t -> t;
    }
}

这个接口继承Function接口，Funtion接口，定义了一个apply的抽象类，接收一个泛型T对象，并且返回泛型R对象

这个接口，只接收一个泛型参数T，集成Function接口，也就是说，传入泛型T类型的参数，调用apply后，返回也T类型的参数；这个接口定义了一个静态方法，返回泛型对象的本身

简单例子

public class M1 {

    public static void main(String[] args) {

        UnaryOperator<Integer> u1 = integer ->
                integer + 100;

        System.out.println(u1.apply(100));

        System.out.println("-----------");

        List<String> strings = Arrays.asList(
                "asas",
                "ddd",
                "csd"
        );

        UnaryOperator<String> unaryOperator = s ->
                s;

        for (String s : strings) {
            System.out.println(unaryOperator.apply(s));
        }

        System.out.println("-----------");

        List<Integer> list = Arrays.asList(10,20,30,40,50);

        UnaryOperator<Integer> unaryOperator2 = integer -> integer*integer;

        unaryOperatorFun(unaryOperator2,list)
                .forEach(System.out::println);

        
    }

    private static List<Integer> unaryOperatorFun(UnaryOperator<Integer> unaryOpt, List<Integer> list){
        List<Integer> uniList = new ArrayList<>();
        list.forEach(i->uniList.add(unaryOpt.apply(i)));
        return uniList;
    }


}

DoubleUnaryOperator IntUnaryOperator LongUnaryOperator

public class M2{

    public static void main(String[] args) {

        DoubleUnaryOperator o1 = d ->

                d + d * 12.36;

        System.out.println(o1.applyAsDouble(12.58));

        System.out.println("-------------------------");

        IntUnaryOperator o2 = i ->
                (int) (i * 100 + 236.22);

        System.out.println(o2.applyAsInt(121));

        System.out.println("-------------------------");

        LongUnaryOperator longUnaryOperator = l ->

                (long) (l * 12.36 + 96.33);

        System.out.println(longUnaryOperator.applyAsLong(1212));



    }
}

BinaryOperator extends BiFunction<T,T,T>

源码:

@FunctionalInterface
public interface BinaryOperator<T> extends BiFunction<T,T,T> {
   
    public static <T> BinaryOperator<T> minBy(Comparator<? super T> comparator) {
        Objects.requireNonNull(comparator);
        return (a, b) -> comparator.compare(a, b) <= 0 ? a : b;
    }

    
    public static <T> BinaryOperator<T> maxBy(Comparator<? super T> comparator) {
        Objects.requireNonNull(comparator);
        return (a, b) -> comparator.compare(a, b) >= 0 ? a : b;
    }
}

BinaryOperator 二元操作符， 传入的两个参数的类型和返回类型相同,继承BiFunction

public class M1 {


    public static void main(String[] args) {

        BinaryOperator<Integer> b1 = (i1,i2) -> i1 + i2;

        System.out.println(compute_1(100,150,b1));

        System.out.println("-----------------");

        System.out.println(compute_1(102,145,(x,y) -> x * y));

        System.out.println("-----------------");

        BinaryOperator<String> b2 = (s1,s2) -> s1.length() + "---" + s2.length();

        System.out.println(b2.apply("abc","123456"));



    }


    public static Integer compute_1(int a1,int a2,BinaryOperator<Integer> binaryOperator){
        return binaryOperator.apply(a1,a2);

    }
}




public class Student {

    private String name;
    private Integer age;
    private String className;
    public Student(String name,Integer age, String className){
        this.name=name;
        this.age=age;
        this.className = className;
    }
    public String getName() {
        return name;
    }
    public Integer getAge() {
        return age;
    }
    public String getClassName() {
        return className;
    }
}


public class M2 {

    public static void main(String[] args) {

        Student s1 = new Student("Shyam", 22,"A");
        Student s2 = new Student("Ram",23,"A");
        Student s3 = new Student("Mohan",22,"B");
        Student s4 = new Student("Ramesh",21,"B");
        List<Student> list = Arrays.asList(s1,s2,s3,s4);


        Comparator<Student> comparator = Comparator.comparing(Student::getAge);

        //Using BinaryOperator.maxBy
        System.out.println("---BinaryOperator.maxBy---");

        Map<String, Optional<Student>> map = list.stream()
                .collect(Collectors.groupingBy(Student::getClassName,
                        Collectors.reducing(BinaryOperator.maxBy(comparator))));

        map.forEach((k,v)->System.out.println("Class:"+k+" Age:"+
                ((Optional<Student>)v).get().getAge()+" Name:"+((Optional<Student>)v).get().getName()));

        //---BinaryOperator.maxBy---
        //Class:A Age:23 Name:Ram
        //Class:B Age:22 Name:Mohan
        System.out.println("");
    }
}

DoubleBinaryOperator IntBinaryOperator LongBinaryOperator

public class M3 {

    public static void main(String[] args) {

        DoubleBinaryOperator doubleBinaryOperator = (d1,d2) ->

                d1*12.36 + d2 * 23.369;

        System.out.println(doubleBinaryOperator.applyAsDouble(10.25,236.69));

        System.out.println("-----------------");


        IntBinaryOperator intBinaryOperator = (i1,i2) ->

                i1 + i2;

        System.out.println(intBinaryOperator.applyAsInt(100,3000));

        System.out.println("-----------------");

        LongBinaryOperator longBinaryOperator = (l1,l2) ->

                l1 * l2;

        System.out.println(longBinaryOperator.applyAsLong(125L,20L));




    }
}