java8新特性Stream和lambda案例（策略模式）

1、Employee类

package com.example.demo;


public class Employee {
    private String name;
    private int age;
    private double salary;

    @Override
    public String toString() {
        return "Employee{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", salary=" + salary +
                '}';
    }

    public Employee(String name, int age, double salary) {
        this.name = name;
        this.age = age;
        this.salary = salary;
    }

    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;
    }



}

2、IEmployee接口

package com.example.demo;

public interface IEmployee {
    public boolean test(T t);
}

3、FilterEmployeeBySalary实现类

package com.example.demo;

public class FilterEmployeeBySalary implements IEmployee{
    @Override
    public boolean test(Employee t) {
        return t.getSalary()>2;
    }
}

4、FilterEmployeeByAge实现类

package com.example.demo;

public class FilterEmployeeByAge implements IEmployee{

    @Override
    public boolean test(Employee t) {
        return t.getAge() > 18;
    }
}

5、DemoApplicationTests测试方法

package com.example.demo;

import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

@SpringBootTest
class DemoApplicationTests {

    List list = Arrays.asList(
            new Employee("A", 18, 2),
            new Employee("B", 20, 3),
            new Employee("C", 30, 4),
            new Employee("D", 11, 5)
    );

    @Test
    void contextLoads() {
        List employees = filterEmployees(list);
        for (Employee emp : employees) {

            System.out.println(emp.toString());
        }
    }

    //需求1：获取年龄大于18的员工
    public List filterEmployees(List list) {
        List emps = new ArrayList<>();
        for (Employee emp : list) {
            if (emp.getAge() > 18) {
                emps.add(emp);
            }
        }
        return emps;
    }

    //需求2：获取工资大于2的员工
    public List filterEmployees2(List list) {
        List emps = new ArrayList<>();
        for (Employee emp : list) {
            if (emp.getSalary() > 2) {
                emps.add(emp);
            }
        }
        return emps;
    }


    @Test
    void test1() {
        List employees = filterEmployee(list, new FilterEmployeeByAge());
        for (Employee emp : employees) {
            System.out.println(emp.toString());
        }
        List employees2 = filterEmployee(list, new FilterEmployeeBySalary());
        for (Employee emp : employees) {
            System.out.println(emp.toString());
        }


    }

    //优化1:策略设计模式优化
    public List filterEmployee(List list, IEmployee mp) {
        List emps = new ArrayList<>();
        for (Employee emp : list) {
            if (mp.test(emp)) {
                emps.add(emp);
            }
        }
        return emps;
    }

    //优化2:匿名内部类优化(相比于1不用创建更多的类)
    @Test
    void test2() {
        final List employees = filterEmployee(list, new IEmployee() {
            @Override
            public boolean test(Employee employee) {
                return employee.getAge() > 18;
            }
        });
        for (Employee emp : employees) {
            System.out.println(emp.toString());
        }


    }

    //优化3:Lambada表达式(相对于匿名内部类优化)
    @Test
    void test3() {
        final List employees = filterEmployee(list, (e) -> e.getAge() > 18);
        employees.forEach(System.out::println);


    }

    //优化4:Stream API
    @Test
    void test4() {
        list.stream()
            .filter((e) -> e.getAge() > 18)
            .forEach(System.out::println);

        //获取所有的名字
        list.stream().map(Employee::getName).forEach(System.out::println);

    }


}