java8新特性学习笔记

package com.abing;

import org.apache.commons.lang.StringUtils;

import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;

/**
 * Created on 18/7/31 by bingyin.gby.
 */
public class Java8Test {

    public static void main(String[] args) {

        //将1个判断输入值字符串否为空，非空则输出，否则赋予默认值
        String s=null;
        String brandId= Optional.ofNullable(s).orElse("123456");

        List<String> names= Arrays.asList("bingyingao","tieyi");


        //遍历集合得到一个新的集合
        List<String> newNames= names.stream().filter(b-> StringUtils.contains(b,"tieyi")).map(a->"prefix"+a).collect(
            Collectors.toList());
        System.out.println("newNames:");
        newNames.forEach(System.out::println);

        //遍历原集合并且对原集合中对象进行操作???
        names.stream().map(a->a+"sufix");
        System.out.println("names:");
        names.forEach(System.out::println);
        new Java8Test().resetUserName();


        //定义function函数并且调用:list转set
        Function<List<String>,Set<String>> listToMap= list->list.stream().collect(Collectors.toSet());
        Set<String> names1=listToMap.apply(Arrays.asList("tieyi","tieyi","bingyingao"));
        System.out.println("listToSet:");
        names1.forEach(System.out::println);

        //所有用户的年龄进行求和,reduce
        new Java8Test().sumUserAge();
        //所有用户的年龄最大、最小、平均，求sum
        new Java8Test().intSummaryStatistics();
        //根据年龄排序
        new Java8Test().sortAgeAsc();

        //遍历map集合
        Map<String,String> classUnit=new HashMap<String,String>(){{
            put("class1","stu1,stu2");
            put("class2","stu2,stu3");
        }};
        classUnit.forEach((k,v)->System.out.println(k+":"+v));

        //遍历int数组
        int[] luckNums={0,8,5,6,7};
        Arrays.stream(luckNums).forEach(System.out::println);
        //遍历字符串数组
        String[] charsArrays="a,c,d,b".split(",");
        Arrays.sort(charsArrays);
        Arrays.asList(charsArrays).stream().forEach(a->System.out.println(a));
        //flatmap的用法

      // java8遍历map
        map.forEach((key, val) -> System.out.println(key + "-->" + val));

    }


    /**
     * 给用户名重设值
     */
    private void resetUserName(){
        List<Java8Test.UserInfo> userInfoList= Arrays.asList(new Java8Test.UserInfo("tieyi"),new Java8Test.UserInfo("bingyingao"));
        userInfoList.forEach(u->u.setName(u.getName()+"suFix"));
        userInfoList.forEach(a->System.out.println(a.getName()));
    }

    /**
     * 累加用户年龄
     */
    private void sumUserAge(){
        List<Java8Test.UserInfo> userInfoList= Arrays.asList(new Java8Test.UserInfo("tieyi",30),new Java8Test.UserInfo("bingyingao",31));
        Integer sumAge= userInfoList.stream().map(a->a.getAge()).reduce((a,b)->a=a+b).get();
        System.out.println(sumAge);


    }


    /**
     * 最佳统计方法
     */
    private void intSummaryStatistics(){
        List<Java8Test.UserInfo> userInfoList= Arrays.asList(new Java8Test.UserInfo("tieyi",30),new Java8Test.UserInfo("bingyingao",31));
        IntSummaryStatistics intSummaryStatistics= userInfoList.stream().mapToInt(a->a.getAge()).summaryStatistics();
        System.out.println(intSummaryStatistics.getAverage());
        System.out.println(intSummaryStatistics.getCount());
        System.out.println(intSummaryStatistics.getMax());
        System.out.println(intSummaryStatistics.getMin());
        System.out.println(intSummaryStatistics.getSum());




    }


    /**
     * 根据用户年龄由低到高排序
     */
    private void sortAgeAsc(){
        List<Java8Test.UserInfo> userInfoList= Arrays.asList(new Java8Test.UserInfo("tieyi",30),new Java8Test.UserInfo("bingyingao",31),new Java8Test.UserInfo("abing",29));
        //由低到高正序
        userInfoList.sort(Comparator.comparingInt(Java8Test.UserInfo::getAge));
        //由高到低正序
        userInfoList.sort(Comparator.comparingInt(Java8Test.UserInfo::getAge).reversed());
        userInfoList.forEach(a->System.out.println(a.getAge()));

    }

#list转为map
    private void list2Map(){
      Map<Long,TppItem> tppItemMap=items.stream().collect(Collectors.toMap(TppItem::getItemId,v->v,(k1,k2)->k1));
}




    public   class UserInfo{


        String name ="";
        int age;
        UserInfo(String name ){
            this.name=name;
        }
        UserInfo(int age){
            this.age=age;
        }

        UserInfo(String name,int age){
            this.name=name;
            this.age=age;
        }
        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;
        }
    }
}