java8中的stream对List的一些操作

java 8中新增了Stream流，大大简化了对各种数据类型的操作；

下面我总结了一些Stream对各种数据结构的操作；

准备数据：

public class Student {
    
    private String age;
    private Integer sex;
    public String getAge() {
        return age;
    }
    public void setAge(String age) {
        this.age = age;
    }
    public Integer getSex() {
        return sex;
    }
    public void setSex(Integer sex) {
        this.sex = sex;
    }
}

public class Demo {
    
    private String name;
    private String age;
    private Integer sex;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getAge() {
        return age;
    }
    public void setAge(String age) {
        this.age = age;
    }
    public Integer getSex() {
        return sex;
    }
    public void setSex(Integer sex) {
        this.sex = sex;
    }
    public Demo(String age, Integer sex) {
        super();
        this.age = age;
        this.sex = sex;
    }
}

一.List

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class Test {
    
    @org.junit.Test
    public void test() {
         List list = new ArrayList<>();  
         Student student1 = new Student();student1.setAge("12");student1.setSex(0);  
         Student student2 = new Student();student2.setAge("13");student2.setSex(2);  
         Student student3 = new Student();student3.setAge("11");student3.setSex(1);  
         Student student4 = new Student();student4.setAge("18");student4.setSex(1);  
         Student student5 = new Student();student5.setAge("18");student5.setSex(0);  
         Student student6 = new Student();student6.setAge("18");student6.setSex(2);  
         Student student7 = new Student();student7.setAge("18");student7.setSex(2);  
         list.add(student1);  
         list.add(student2);  
         list.add(student3);  
         list.add(student4);  
         list.add(student5);  
         list.add(student6);  
         list.add(student7);  
         List demos = new ArrayList();
         demos = printData(demos, list);
//         printSexequal0(demos);
//         filterAge(demos);
//         sort(demos);
//         pour(demos);
//         pour2(demos);
//         moreSort(demos);
//         morePour(demos);
         groupByAge(demos);
         
    }
    
    /**
     * 数据打印
     * @param demos
     * @param list
     */
    public List printData(List demos ,List list) {
        demos = list.stream().map(student -> new Demo(student.getAge(),student.getSex())).collect(Collectors.toList());
        /*demos.forEach(demo ->{
            System.out.println(demo.getAge());
        });*/
        return demos;
    }
    
    /**
     * 打印性别为0的数据
     * @param demos
     */
    public void printSexequal0(List demos) {
        List collect = demos.stream().filter(demo -> demo.getSex() == 0).distinct().collect(Collectors.toList());
        collect.forEach(item ->{
            System.out.println("\n"+item.getAge()+":"+item.getSex());
        });
    }
    
    /**
     * 过滤年龄大于12的信息
     * @param demos
     */
    public void filterAge(List demos) {
        List collect = demos.stream().filter(demo -> Integer.valueOf(demo.getAge())>12).collect(Collectors.toList());
        collect.forEach(demo ->{
            System.out.println(demo.getAge()+":"+demo.getSex());
        });
    }
    
    /**
     * 数据排序
     * @param demos
     */
    public void sort(List demos) {
        List collect = demos.stream().sorted((s1,s2) -> s1.getAge().compareTo(s2.getAge())).collect(Collectors.toList());
        collect.forEach(demo -> {
            System.out.println(demo.getAge());
        });
    }
    
    /**
     * 倒叙
     * @param demos
     */
    public void pour(List demos) {
        ArrayList demoArray = (ArrayList)demos;
        demoArray.sort(Comparator.comparing(Demo::getAge).reversed());
        demoArray.forEach(demo -> {
            System.out.println(demo.getAge());
        });
    }
    
    /**
     * 倒叙2
     * @param demos
     */
    public void pour2(List demos) {
        ArrayList demoArray = (ArrayList)demos;
        Comparator comparator = (h1,h2) -> h1.getAge().compareTo(h2.getAge());
        demoArray.sort(comparator.reversed());
        demoArray.forEach(demo -> {
            System.out.println(demo.getAge());
        });
    }
    
    /**
     * 多条件排序--正序
     * @param demos
     */
    public void moreSort(List demos) {
        demos.sort(Comparator.comparing(Demo::getSex).thenComparing(Demo::getAge));
        demos.forEach(demo ->{
            System.out.println(demo.getSex()+":"+demo.getAge());
        });
    }
    
    /**
     * 多条件倒叙
     * @param demos
     */
    public void morePour(List demos) {
        demos.sort(Comparator.comparing(Demo::getSex).reversed().thenComparing(Demo::getAge));
        demos.forEach(demo ->{
            System.out.println(demo.getSex()+":"+demo.getAge());
        });
    }

    /**
     * 分组
     * @param demos
     */
    public void groupByAge(List demos) {
        Map> collect = demos.stream().collect(Collectors.groupingBy(Demo::getAge));
        collect.forEach((key,value)->{
            value.forEach(demo ->{
                System.out.println(key+":"+demo.getSex());
            });
        });
    }
}

 filter

    @SuppressWarnings("unused")
    public void filterTest(List demos) {
        String age = "12";
        String sex = "0";
        List collect = demos.stream().filter(demo -> {
            if(age!=null) {
                return Integer.parseInt(demo.getAge())>Integer.parseInt(age);
            }else {
                return true;
            }
        }).filter(demo ->{
            if(sex!=null) {
                return demo.getSex() ==Integer.parseInt(sex);
            }else {
                return true;
            }
        }).collect(Collectors.toList());
        
        collect.forEach(demo ->{
            System.out.println(demo.getAge()+":"+demo.getSex());
        });
    }

 多条件排序和去重复测试

    @Test
    public void testMoreSort() {
        List list = new ArrayList<>();
        Entrys item = new Entrys();
        item.setOne(1);
        item.setTwo(1);
        Entrys item1 = new Entrys();
        item1.setOne(1);
        item1.setTwo(2);
        Entrys item2 = new Entrys();
        item2.setOne(1);
        item2.setTwo(3);
        Entrys item3 = new Entrys();
        item3.setOne(1);
        item3.setTwo(4);
        
        Entrys item4 = new Entrys();
        item4.setOne(2);
        item4.setTwo(1);
        Entrys item5 = new Entrys();
        item5.setOne(2);
        item5.setTwo(2);
        Entrys item6 = new Entrys();
        item6.setOne(2);
        item6.setTwo(3);
        Entrys item7 = new Entrys();
        item7.setOne(2);
        item7.setTwo(4);
        
        Entrys item8 = new Entrys();
        item8.setOne(3);
        item8.setTwo(1);
        Entrys item9 = new Entrys();
        item9.setOne(3);
        item9.setTwo(2);
        Entrys item10 = new Entrys();
        item10.setOne(3);
        item10.setTwo(3);
        Entrys item11 = new Entrys();
        item11.setOne(4);
        item11.setTwo(4);
        
        
        list.add(item1);
        list.add(item2);
        list.add(item3);
        list.add(item4);
        list.add(item5);
        list.add(item6);
        list.add(item7);
        list.add(item8);
        list.add(item9);
        list.add(item10);
        list.add(item11);
        list.sort(Comparator.comparing(Entrys::getOne).thenComparing(Entrys::getTwo));
        list.forEach(demo ->{
            System.out.println(demo.getOne()+":"+demo.getTwo());
        });
    }
    
    @Test
    public void testDic() {
        List list = new ArrayList<>();
        Models model = new Models();
        model.setName("111");
        model.setAge("238");
        model.setSemi_fid("xxxcqqccbbb");
        model.setTid("111111");
        Models model1 = new Models();
        model1.setName("11122312");
        model1.setAge("237");
        model1.setSemi_fid("xxxccqcbbb");
        model1.setTid("11111133");
        Models model2 = new Models();
        model2.setName("111333123");
        model2.setAge("236");
        model2.setSemi_fid("xxxccqcbbb");
        model2.setTid("111111");
        Models model3 = new Models();
        model3.setName("1113213");
        model3.setAge("236");
        model3.setSemi_fid("xxxccqqcbbb");
        model3.setTid("111111");
        Models model4 = new Models();
        model4.setName("feng");
        model4.setAge("25");
        model4.setSemi_fid("xxxcccqqqbbb");
        model4.setTid("111111");
        
        Models model5 = new Models();
        model5.setName("hao");
        model5.setAge("23");
        model5.setSemi_fid("xxxcccqqqbbb");
        model5.setTid("111111");
        
        list.add(model);
        list.add(model1);
        list.add(model2);
        list.add(model3);
        list.add(model4);
        list.add(model5);
                //顺序不变
        List collect = list.stream().distinct().collect(Collectors.toList());
        collect.forEach(demo ->{
            System.out.println(demo.getName()+":"+demo.getAge()+":"+demo.getSemi_fid()+":"+demo.getTid());
        });
        //顺序发生变化
//        List distinctClass = classEntities.stream().
//        collect(
//        Collectors.collectingAndThen(
//        Collectors.toCollection(
//        () -> new TreeSet<>(
//        Comparator.comparing(o -> o.getProfessionId() + ";" + o.getGrade()
//        ))), ArrayList::new));
/*        ArrayList collect = list.stream().
        collect(
                Collectors.collectingAndThen(
                        Collectors.toCollection(
                                () ->new TreeSet(
                                        Comparator.comparing(demo -> demo.getSemi_fid()+";"+demo.getTid())
                                        )
                                ), ArrayList::new)
                );
        
        collect.forEach(demo ->{
            System.out.println(demo.getName()+":"+demo.getAge()+":"+demo.getSemi_fid()+":"+demo.getTid());
        });*/

    }
}

class Entrys{
    
    private int one;
    
    private int two;

    public int getOne() {
        return one;
    }

    public void setOne(int one) {
        this.one = one;
    }

    public int getTwo() {
        return two;
    }

    public void setTwo(int two) {
        this.two = two;
    }

public class Models {

    private String name;
    
    private String semi_fid;
    
    private String tid;
    
    private String age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSemi_fid() {
        return semi_fid;
    }

    public void setSemi_fid(String semi_fid) {
        this.semi_fid = semi_fid;
    }

    public String getTid() {
        return tid;
    }

    public void setTid(String tid) {
        this.tid = tid;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    @Override
    public int hashCode() {
        return (this.getSemi_fid()+this.getTid()).hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if(obj instanceof Models) {
            Models item = (Models)obj;
            if(this.getSemi_fid().equals(item.getSemi_fid()) && this.getTid().equals(item.getTid())) {
              return true;    
            }else {
                return false;
            }
        }else {
            return false;
        }
    }

}