filter()方法数据过滤

 数据过滤类似于SQL中的WHERE语句，是在杂乱的数据中筛选出需要的数据。下面就介绍一下filter()方法。

filter()是Stream接口提供的一个过滤方法。该方法以lambda表达式的逻辑过滤流中的元素。若要展示数据需可以使用 Stream提供的collect（）方法进行封装。

基本使用方法：

下面是一个简单的例子，展示了如和利用filter（）过滤出3的倍数：

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Filtertest {
    public static void main(String[] args) {
        List<Integer>list  = new ArrayList<>();
        for(int i = 1;i<=30;i ++){
            list.add(i);                                //向集合中添加数据
        }
        printeach("过滤前" ,list);
        Stream<Integer>stream = list.stream();         //获取集合流对象
        stream= stream.filter(n-> n % 3 == 0);         //过流出流中3的倍数（关键代码）
        List<Integer>res = stream.collect(Collectors.toList());//将流重新封装成List集合
 
        printeach("过滤后",res);
 
    }
    static void printeach(String S,List list)
    {   System.out.print(S);
        list.stream().forEach(n->{
            System.out.print(n+" ");
        });  //不要忘记分号
        System.out.println(" ");
    }
 
}

运行结果如下： 

过滤前1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  
过滤后3 6 9 12 15 18 21 24 27 30  

2 .结合流处理用

filter()方法通常会和流处理一起用。而且过滤的不仅仅是数字。下面这个例子首先添加了一个员工集合。并记录了姓名，年龄，薪资，性别，部门。最后通过filter()方法找出了女性的员工。

代码如下：

import java.util.List;
import java.util.ArrayList;
import java.util.stream.Stream;
import java.util.stream.Collectors;
public class Streamprocess{
    private String name;
    private int age;
    private double salary;
    private String sex;
    private String dept;
    public Streamprocess(String name,int age,double salary,String sex, String dept)
    {
        this.name = name;
        this.age =age;
        this.salary = salary;
        this.sex = sex;
        this.dept = dept;
    }
    public String toString() {
        return "name="+name+"age="+age+"salary="+salary+"sex="+sex+"dept="+dept;
    }
    public String getName() { return name;}
    public int getAge() {return age;}
    public double getSalary() {return salary;}
    public String getSex() {return sex;}
    public String getDept() {return dept;}
    static List<Streamprocess>getEm(){
    List<Streamprocess>list = new ArrayList<Streamprocess>();
    list.add(new Streamprocess("小一",50,4000,"男","一部"));
    list.add(new Streamprocess("小二",10,4000,"女","一部"));
    list.add(new Streamprocess("小三",30,5000,"男","二部"));
    list.add(new Streamprocess("小四",40,5000,"男","二部"));
    list.add(new Streamprocess("小五",60,3000,"女","三部"));
    list.add(new Streamprocess("小六",10,4000,"男","三部"));
    return list;
    }
    public static void main(String[] args) {
        List<Streamprocess>list1 = Streamprocess.getEm();
        Stream<Streamprocess>stream = list1.stream();
        stream = stream.filter(people->"女".equals(people.getSex()));
        List<Streamprocess>result = stream.collect(Collectors.toList());
        for(Streamprocess emp:result) {
            System.out.println(emp);
 
        }
    }
}

运行结果：

name=小二age=10salary=4000.0sex=女dept=一部
name=小五age=60salary=3000.0sex=女dept=三部

希望对你有帮助~~~