黑马JAVA P141 Stream流体系

package com.itheima.d2_stream;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * 初步体验Stream流的方便与快捷
 */
public class StreamTest {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        Collections.addAll(names,"张三丰","张无忌","周芷若","赵敏","张强");
        System.out.println(names);

//        //1.从集合中找出姓张的放到新集合
//        List<String> zhanglist = new ArrayList<>();
//        for (String name : names) {
//            if(name.startsWith("张")){
//                zhanglist.add(name);
//            }
//        }
//        System.out.println(zhanglist);
//
//        //2.找名称长度是3的姓名
//        List<String> zhangThreelist = new ArrayList<>();
//        for (String name : zhanglist) {
//            if(name.length() ==3){
//                zhangThreelist.add(name);
//            }
//        }
//        System.out.println(zhangThreelist);

        //3.使用Stream实现的
        names.stream().filter(s -> s.startsWith("张")).filter(s -> s.length() == 3).forEach(s -> System.out.println(s));
    }
}

package com.itheima.d2_stream;

import java.util.*;
import java.util.stream.Stream;

public class StreamDemo02 {
    public static void main(String[] args) {
        /**-----------Collection集合获取流-------------- */
        Collection<String> list = new ArrayList<>();
        Stream<String> s = list.stream();

        /**---------------Map集合获取流---------------*/
        Map<String, Integer> maps = new HashMap<>();
        //键流
        Stream<String> keyStream = maps.keySet().stream();
        //值流
        Stream<Integer> valueStream = maps.values().stream();
        //键值对流（拿整体）
        Stream<Map.Entry<String,Integer>> keyAndValueStream = maps.entrySet().stream();

        /**----------------数组获取流------------------*/
        String[] names = {"赵敏","小昭","灭绝","周芷若"};
        Stream<String> nameStream = Arrays.stream(names);
        Stream<String> nameStream2 = Stream.of(names);

    }
}

package com.itheima.d2_stream;

import jdk.nashorn.internal.runtime.linker.LinkerCallSite;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Stream;

/**
 * 目标：Stream流的常用API
 * forEach:逐一处理(遍历)
 * count:统计个数
 * --long count();
 * filter: 过滤元素
 * -- Stream<T> filter(Predicate<? super T> predicate)
 * limit: 取前几个元素
 * skip：跳过前几个
 * map：加工方法
 * concat：合并流
 */
public class StreamDemo03 {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("张无忌");
        list.add("周芷若");
        list.add("赵敏");
        list.add("张强");
        list.add("张三丰");
        list.add("张三丰");
        list.stream().filter( s ->  s.startsWith("张")).forEach(s -> System.out.println(s));

        long size = list.stream().filter(s -> s.length() == 3).count();
        System.out.println(size);

//        list.stream().filter( s ->  s.startsWith("张")).limit(2).forEach(s -> System.out.println(s));
        list.stream().filter( s ->  s.startsWith("张")).limit(2).forEach( System.out::println);

        list.stream().filter( s ->  s.startsWith("张")).skip(2).forEach( System.out::println);

        //map加工方法：第一个参数原材料  -> 第二个参数是加工后的结果。
        //给集合元素的前面加上一个： 黑马的
        list.stream().map(s -> "黑马的:" + s).forEach(a -> System.out.println(a));

        //需求：把所有的名称  都加工成一个学生对象。
        list.stream().map(s -> new Student(s)).forEach(s -> System.out.println(s));
//        list.stream().map(Student::new).forEach(System.out :: println); //构造器引用  方法引用

        //合并流。
        Stream<String> s1 = list.stream().filter(s -> s.startsWith("张"));
        Stream<String> s2 =Stream.of("java1","java2");
//        public static <T> Stream<T> concat(Stream<? extends T> a, Stream<? extends T> b)
        Stream<String> s3 = Stream.concat(s1,s2);
        s3.distinct().forEach(s -> System.out.println(s));
    }
}

package com.itheima.d2_stream;

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;

public class StreamDemo04 {
    public static double allMoney ;
    public static double allMoney2 ; // 两个部门去掉最高工资，最低工资的总和

    public static void main(String[] args) {
        List<Employee> one = new ArrayList<>();
        one.add(new Employee("猪八戒",'男',30000,25000,null));
        one.add(new Employee("孙悟空",'男',25000,1000,"顶撞上司"));
        one.add(new Employee("沙僧",'男',20000,20000,null));
        one.add(new Employee("小白龙",'男',20000,25000,null));

        List<Employee> two = new ArrayList<>();
        one.add(new Employee("武松",'男',15000,9000,null));
        one.add(new Employee("李逵",'男',20000,10000,null));
        one.add(new Employee("西门庆",'男',50000,10000,"被打"));
        one.add(new Employee("潘金莲",'女',3500,1000,"被打"));
        one.add(new Employee("武大郎",'女',20000,0,"下毒"));

        //1.开发一部的最高工资的员工
        //制定大小规则了
//        Employee e = one.stream().max((e1,e2) -> Double.compare(e1.getSalary() + e1.getBonus(), e2.getSalary() + e2.getBonus())).get();
//        System.out.println(e);

        Topperformer t= one.stream().max((e1,e2) -> Double.compare(e1.getSalary() + e1.getBonus(), e2.getSalary() + e2.getBonus()))
                        .map(e -> new Topperformer(e.getName(), e.getSalary() + e.getBonus())).get();
        System.out.println(t);

        //2.统计平均工资，去掉最高工资和最低工资
        one.stream().sorted((e1,e2) -> Double.compare(e1.getSalary() + e1.getBonus(), e2.getSalary() + e2.getBonus()))
                .skip(1).limit(one.size() - 2).forEach(e ->{
                    //求出总和：剩余员工的工资总和
                    allMoney += (e.getSalary() + e.getBonus());
                });
        System.out.println("开发一部的平均工资是：" + allMoney / (one.size() - 2));

        //3.合并2个集合流，再统计
        Stream<Employee> s1 = one.stream();
        Stream<Employee> s2 = two.stream();
        Stream<Employee> s3 = Stream.concat(s1, s2);
        s3.sorted((e1,e2) -> Double.compare(e1.getSalary() + e1.getBonus(), e2.getSalary() + e2.getBonus()))
                .skip(1).limit(one.size() + two.size() - 2).forEach(e ->{
                    //求出总和：剩余员工的工资总和
                    allMoney2 += (e.getSalary() + e.getBonus());
                });
//        BigDecimal
        BigDecimal a = BigDecimal.valueOf(allMoney2);
        BigDecimal b = BigDecimal.valueOf(one.size() + two.size() - 2);
        System.out.println("开发部的平均工资是：" + a.divide(b,2, RoundingMode.HALF_UP));
    }
}

package com.itheima.d2_stream;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * 目标：手机Stream流的数据到 集合或者数组中去。
 */
public class StreamDemo05 {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("张无忌");
        list.add("周芷若");
        list.add("赵敏");
        list.add("张强");
        list.add("张三丰");
        list.add("张三丰");

        Stream<String> s1 = list.stream().filter(s -> s.startsWith("张"));
        List<String> zhangList = s1.collect(Collectors.toList()); //可变集合
        System.out.println(zhangList);

//        List<String> list1 = s1.toList(); //得到不可变集合
//        list1.add("java");
//        System.out.println(list1);

        //注意注意注意："流只能使用一次"
        Stream<String> s2= list.stream().filter(s -> s.startsWith("张"));
        Set<String> zhangSet = s2.collect(Collectors.toSet());
        System.out.println(zhangSet);

        Stream<String> s3= list.stream().filter(s -> s.startsWith("张"));
//    Object[] arrs = s3.toArray();
        String [] arrs = s3.toArray(String[] ::new); //可以不管，拓展一下思维！！
        System.out.println("Arrays数组内容：" + Arrays.toString(arrs));
    }
}