package com.day0328_1;
import org.junit.jupiter.api.Test;
import java.io.PrintStream;
import java.util.Comparator;
import java.util.function.BiPredicate;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Supplier;
/**
 * 方法引用的使用
 *
 *  1.使用情境：当要传递给Lambda体的操作，已有实现的方法了，可以使用方法引用!
 *
 *  2.方法引用，本质上就是Lambda表达式，而Lambda表达式作为函数式接口的实例。所有
 *  方法引用，也是函数式接口的实例。
 *
 *  3.使用格式    类（或对象）::方法名
 *
 *  4.具体分为如下的三种情况：
 *  对象  :: 非静态方法
 *  类   :: 静态方法
 *
 *  类   :: 非静态方法
 *
 *  5.方法引用的使用要求：要求接口中的抽象方法的形参列表和返回值类型与方法引用的方法的
 *  形参列表和返回值类型都相同（针对于情况一和情况二）
 *
 *
 */
public class MethodRefTest {
    //情境一：   对象::实例方法
    //Consumer中的void accept(T t)
    //PrintStream中的void println(T t)
    @Test
    public void test1(){
        Consumer<String> con1=str -> System.out.println(str);
        con1.accept("北京");
        System.out.println("****************");
        PrintStream ps=System.out;
        Consumer<String> con2=ps::println;
        con2.accept("beijing");
    }
    //Supplier中的T get()
    //Employee 中的String getName()
    @Test
    public void test2(){
        Employee emp= new Employee(1001,"Tom",23,5600);
        Supplier<String> sup1=()-> emp.getName();
        System.out.println(sup1.get());
        System.out.println("****************");
        Supplier<String> sup2=emp::getName;
        System.out.println(sup2.get());
    }
    //情况二： 类::静态方法
    //Comparator中的int compare(T t1,T t2)
    //Integer中的int compare(T t1,T t2)
    @Test
    public void test3(){
        Comparator<Integer> com1=(t1,t2)->Integer.compare(t1,t2);
        System.out.println(com1.compare(12,21));
        System.out.println("****************");
        Comparator<Integer> com2 = Integer::compare;
        System.out.println(com2.compare(12,3));
    }
    //Function中的R apply(T t)
    //Math中的Long round (Double d)
    @Test
    public void test4(){
        Function<Double,Long> func=new Function<Double, Long>() {
            @Override
            public Long apply(Double d) {
                return Math.round(d);
            }
        };
        System.out.println("****************");
        Function<Double,Long> func1=d->Math.round(d);
        System.out.println(func1.apply(12.3));
        System.out.println("****************");
        Function<Double,Long> func2=Math::round;
        System.out.println(func2.apply(12.6));
    }
    //情况三：类::实例方法（有难度）
    //Comparator中的int compare(T t1,T t2)
    //String 中的int t1.compareTo(t2)
    @Test
    public void test5(){
        Comparator<String> com1=(s1,s2)->s1.compareTo(s2);
        System.out.println(com1.compare("abc","abd"));
        System.out.println("****************");
        Comparator<String> com2=String::compareTo;
        System.out.println(com2.compare("abd","abm"));
    }
    //BiPredicate中的boolean test(T t1 ,T t2);
    //String 中的boolean t1.equals(t2)
    @Test
    public void test6(){
        BiPredicate<String,String> pre1=(s1,s2)->s1.equals(s2);
        System.out.println(pre1.test("abc","abc"));
        System.out.println("****************");
        BiPredicate<String,String> pre2=String::equals;
        System.out.println(pre2.test("abc","abd"));
    }
    //Function中的R apply(T t)
    //Employee中的String getName();
    @Test
    public void test7(){
        Employee employee=new Employee(1001,"Jerry",23,6000);
        Function<Employee,String> func1=e->e.getName();
        System.out.println(func1.apply(employee));
        System.out.println("****************");
        Function<Employee,String> func2=Employee::getName;
        System.out.println(func2.apply(employee));
    }
}

package com.day0328_1;
import org.junit.jupiter.api.Test;
import java.util.Arrays;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Supplier;
/**
 * 一、构造器引用
 *       和方法引用类似，函数式接口的抽象方法的形参和构造器的形参列表一致，
 *       抽象方法的返回值类型即为构造器所属的类的类型
 *
 * 二、数组引用
 *       大家可以把数组看成一个特殊的类，则写法与构造器引用一致
 *
 *
 */
public class ConstructorRefTest {
    //构造器引用
    //Supplier 中的 T get()
    @Test
    public void test1(){
        Supplier<Employee> sup=new Supplier<Employee>() {
            @Override
            public Employee get() {
                return new Employee();
            }
        };
        System.out.println("*************");
        System.out.println(sup.get());
        Supplier<Employee> sup1=()->new Employee();
        System.out.println(sup1.get());
        System.out.println("*************");
        Supplier<Employee> sup2=Employee::new;
        System.out.println(sup2.get());
    }
    //Function中的R apply(T t)
    @Test
    public void test2(){
        Function<Integer,Employee> func1=id->new Employee(id);
        Employee employee=func1.apply(1001);
        System.out.println(employee);
        System.out.println("*************");
        Function<Integer,Employee> func2=Employee::new;
        Employee employee1=func1.apply(1002);
        System.out.println(employee1);
    }
    //BiFunction中的R apply(T t,U u)
    @Test
    public void test3(){
        BiFunction<Integer,String,Employee>func1=(id,name)->new Employee(id,name);
        System.out.println(func1.apply(1001,"Tom"));
        System.out.println("*************");
        BiFunction<Integer,String,Employee>func2=Employee::new;
        System.out.println(func2.apply(1002,"Tom"));
    }
    //数组引用
    //Function中的R apply(T t)
    @Test
    public void test4(){
        Function<Integer,String[]> func1=length->new String[length];
        String[] arr1=func1.apply(5);
        System.out.println(Arrays.toString(arr1));
        Function<Integer,String[]> func2=String[]::new;
        String[] arr2=func1.apply(10);
        System.out.println(Arrays.toString(arr2));
    }
}

package com.day0328_1;
import java.util.Objects;
public class Employee {
    private int id;
    private String name;
    private int age;
    private double salary;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public double getSalary() {
        return salary;
    }
    public void setSalary(double salary) {
        this.salary = salary;
    }
    public Employee() {
        System.out.println("Employee()....");
    }
    public Employee(int id) {
        this.id = id;
        System.out.println("Employee(int id)....");
    }
    public Employee(int id, String name) {
        this.id = id;
        this.name = name;
    }
    public Employee(int id, String name, int age, double salary) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.salary = salary;
    }
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Employee employee = (Employee) o;
        return id == employee.id &&
                age == employee.age &&
                Double.compare(employee.salary, salary) == 0 &&
                Objects.equals(name, employee.name);
    }
    @Override
    public int hashCode() {
        return Objects.hash(id, name, age, salary);
    }
    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", salary=" + salary +
                '}';
    }
}

package com.day0328_1;
import java.util.ArrayList;
import java.util.List;
/**
 * 提供测试的数据
 *
 */
public class EmployeeData {
    public static List<Employee> getEmployee(){
        List<Employee> list= new ArrayList<>();
        list.add(new Employee(1001,"马化腾",34,6000.38));
        list.add(new Employee(1002,"马云",12,9876.12));
        list.add(new Employee(1003,"刘强东",33,3000.82));
        list.add(new Employee(1004,"雷军",26,7657.37));
        list.add(new Employee(1005,"李彦宏",65,5555.32));
        list.add(new Employee(1006,"比尔盖茨",42,9500.53));
        list.add(new Employee(1007,"任正非",26,4333.32));
        list.add(new Employee(1008,"扎克伯格",35,2500.32));
        return list;
    }
}