Stream系列（一）Filter方法使用

Filter 是过滤器，也可以当查询方法使用

视频讲解: https://www.bilibili.com/video/av76583051/

EmployeeTestCase.java

package com.example.demo;

import lombok.extern.log4j.Log4j2;
import org.junit.Test;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

@Log4j2
public class EmployeeTestCase extends BaseTest{
    @Test
    public void filter() {
        //获取包含Alex员工列表
        List<Employee> employeeIs1 = list.stream().filter(e -> e.getName().contains("Alex")).collect(Collectors.toList());
        assertTrue(null != employeeIs1 && employeeIs1.get(0).getId() == 1l);
        //获取包含Jacks名称的首位员工
        Optional<Employee> employeeJaskFirst2 = list.stream().filter(e -> e.getName().contains("Jack")).findFirst();
        assertEquals(employeeJaskFirst2.get().getId(), 3);
        //获取所有薪酬为1500的员工
        List<Employee> employees1350 = list.stream().filter(employee -> employee.getSalary() == 1500).peek(System.out::println).collect(Collectors.toList());
        assertEquals(2, employees1350.size());
    }
}

BaseTest.java

    package com.example.demo;

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

    public class BaseTest {
        protected static final List<Employee> list = Arrays.asList(
                new Employee(1, "Alex", 1000),
                new Employee(2, "Michael", 2000),
                new Employee(3, "Jack", 1500),
                new Employee(4, "Owen", 1500),
                new Employee(5, "Denny", 2000));

        protected static final List<List<Employee>> listFlat = Arrays.asList(
                Arrays.asList(new Employee(1, "Alex", 1000),
                              new Employee(2, "Michael", 2000)),
                Arrays.asList(new Employee(3, "Jack", 1500),
                              new Employee(4, "Owen", 1500)),
                Arrays.asList(new Employee(5, "Denny", 2000)));
    }

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