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java基础中Collections及collect(toList,toSet,toMap)的用法

package com.gaofeng;import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.Stream;public class demo01 {public static void main(String[] args) {ArrayList<String> list = new ArrayList<>();Collections.addAll(list,"张无忌-男-15","张无忌1-男-15","周芷若-女-20","小昭-女-18","张三丰-男-100","谢逊-男-40");List<String> collect = list.stream().filter(s -> "男".equals(s.split("-")[1])).collect(Collectors.toList());System.out.println(collect);Set<String> collect1 = list.stream().filter(s -> "男".equals(s.split("-")[1])).collect(Collectors.toSet());System.out.println(collect1);boolean contains = collect1.contains("张无忌-男-15");System.out.println(contains);Map<String, Integer> collect2 = list.stream().filter(s -> "男".equals(s.split("-")[1])).collect(Collectors.toMap(new Function<String, String>() {@Overridepublic String apply(String s) {return s.split("-")[0];}}, new Function<String, Integer>() {@Overridepublic Integer apply(String s) {return Integer.parseInt(s.split("-")[2]);}}));System.out.println(collect2);// 简化写法Map<String, Integer> collect3 = list.stream().filter(s -> "男".equals(s.split("-")[1])).collect(Collectors.toMap(s -> s.split("-")[0],s -> Integer.parseInt(s.split("-")[2])));System.out.println(collect3);}
}

• 算法练习1：

一个集合里面添加任意的数字，然后过滤掉技奇数，保留偶数

public class demo02 {public static void main(String[] args) {ArrayList<Integer> list = new ArrayList<>();Collections.addAll(list,1,2,3,4,5,6,7,8,9,10);List<Integer> collect = list.stream().filter(n -> n % 2 == 0).collect(Collectors.toList());System.out.println(collect);}
}

• 算法练习2：

一个集合里面添加如下的姓名和年龄字符串数据，进行过滤处理

ArrayList<String> list = new ArrayList<>();Collections.addAll(list,"张三,23","李四,15","刘旺,30");Map<String, Integer> collect5 = list.stream().filter(s -> Integer.parseInt(s.split(",")[1]) > 24).collect(Collectors.toMap(new Function<String, String>() {@Overridepublic String apply(String s) {return s.split(",")[0];}}, new Function<String, Integer>() {@Overridepublic Integer apply(String s) {return Integer.parseInt(s.split(",")[1]);}}));System.out.println(collect5);Map<String, Integer> collect6 = list.stream().filter(s -> Integer.parseInt(s.split(",")[1]) > 24).collect(Collectors.toMap(s -> s.split(",")[0], s -> Integer.parseInt(s.split(",")[1])));System.out.println(collect6);

• 方法引用
• 
  

public class demo04 {public static void main(String[] args) {Integer[] arr = {1,2,3,4,5,6,7,8,9};
//        Arrays.sort(arr, new Comparator<Integer>(){
//            @Override
//            public int compare(Integer o1, Integer o2) {
//                return o2 - o1;
//            }
//        });
//        Arrays.sort(arr, (Integer o1, Integer o2) -> {
//                return o2 - o1;
//        });
//        Arrays.sort(arr, (o1, o2) -> o2 - o1);Arrays.sort(arr, demo04::compare);System.out.println(Arrays.toString(arr));}public static int compare(Integer o1 ,Integer o2 ){return  o2 - o1;}
}