Stream流

import java.util.function.Predicate;
public class Test03 {
    public static void main(String[] args) {
        Integer[] arr = {-12345, 9999, 520, 0,-38,-7758520,941213};

        //a)   使用lambda表达式创建Predicate对象p1,p1能判断整数是否是自然数
        Predicate<Integer> p1 = (s) -> s>=0;
        //b)   使用lambda表达式创建Predicate对象p2,p2能判断整数的绝对值是否大于100
        Predicate<Integer> p2 = (s) -> Math.abs(s)>100;
        //c)   使用lambda表达式创建Predicate对象p3,p3能判断整数是否是偶数
        Predicate<Integer> p3 = (s) -> s%2==0;

        //e)   遍历arr，仅利用已创建的Predicate对象(不使用任何逻辑运算符)，完成以下需求
        int count1 = 0;
        int count2 = 0;
        int count3 = 0;
        int count4 = 0;
        for (Integer i : arr) {
            //统计自然数个数
            if (p1.test(i)){
                count1++;
            }
            //统计负整数个数
            if (p1.negate().test(i)){
                count2++;
            }
            //统计绝对值大于100的偶数个数
            if (p2.and(p3).test(i)){
                count3++;
            }
            //统计是负整数或偶数的数的个数
            if (p1.negate().or(p3).test(i)){
                count4++;
            }
        }
        //分别打印结果
        System.out.println("自然数的个数为："+count1);
        System.out.println("负整数的个数为："+count2);
        System.out.println("绝对值大于100的偶数的个数为："+count3);
        System.out.println("是负整数或偶数的数的个数为："+count4);
    }
}

import java.util.*;
import java.util.function.Function;
public class Test04 {
    public static void main(String[] args) {
        //1.   使用lambda表达式分别将以下功能封装到Function对象中
        //a)   求Integer类型ArrayList中所有元素的平均数
        Function<ArrayList<Integer>,Integer> f1 = (list)->{
            Integer sum = 0;
            for (Integer i : list) {
                sum+=i;
            }
            return sum/list.size();
        };

        //b)   将Map<String,Integer>中value存到ArrayList<Integer>中
        Function<Map<String,Integer>,ArrayList<Integer>> f2 = (map)->{
            /*ArrayList<Integer> list = new ArrayList<>();
            for (String s : map.keySet()) {
                Integer i = map.get(s);
                list.add(i);
            }*/
            Collection<Integer> values = map.values();
            ArrayList<Integer> list = new ArrayList<>();
            list.addAll(values);
            return list;
        };
        
        //2 将学生姓名和成绩封装到map中
        Map<String,Integer> map = new HashMap<String, Integer>();
        map.put("岑小村", 59);
        map.put("谷天洛", 82);
        map.put("渣渣辉", 98);
        map.put("蓝小月", 65);
        map.put("皮几万", 70);

        //利用Function求平均成绩
        Integer avg = f2.andThen(f1).apply(map);
        System.out.println("学生平均成绩为："+avg);
    }
}

public static void main(String[] args) {
  List<String> list = new ArrayList<>();
  Stream<String> stream1 = list.stream();

  Set<String> set = new HashSet<>();
  Stream<String> stream2 = set.stream();

  Map<String, String> map = new HashMap<>();
  Stream<String> keyStream = map.keySet().stream();
  Stream<String> valueStream = map.values().stream();
  Stream<Map.Entry<String,String>>entryStream = map.entrySet().stream();

  String[] array = {"东邪", "西毒", "南帝", "北丐", "中神通"};
  Stream<String> stream = Stream.of(array);
 }

import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
 	 Stream<String> stream = Stream.of("黄药师", "冯蘅", "郭靖", "黄蓉", "郭芙", "郭襄", "郭破虏");
String[] guos = stream.filter(s -> s.startsWith("郭")).toArray(String[]::new);
 	}
}

import java.util.ArrayList;
public class Test04 {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("陈玄风");
        list.add("梅超风");
        list.add("陆乘风");
        list.add("曲灵风");
        list.add("武眠风");
        list.add("冯默风");
        list.add("罗玉风");


        list.stream().limit(2).forEach(System.out::println);
        list.stream().skip(list.size() - 2).forEach(System.out::println);
    }
}

import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
  	Stream<Integer> stream = Stream.of(1, -2, -3, 4,-5);
stream.map(Math::abs).forEach(System.out::println);
 	}
}

import java.util.stream.Stream;
public class Test {
public static void main(String[] args) {
  	Stream<String> streamA = Stream.of("郭靖", "杨康");
Stream<String> streamB = Stream.of("黄蓉", "穆念慈");
List<String> strList = Stream.concat(streamA, streamB).collect(Collectors.toList());
 	}
}

public class Test {
public static void main(String[] args) {
  	Collection<String> coll = new ArrayList<>();
  	Stream<String> parallelStream1 = coll.parallelStream();

Stream<Integer> parallelStream2 = Stream.of(100, 200, 300, 400).parallel();
 	}
}