Lambada List集合操作实例(最全最容易理解)

package com.example.projectmain; import java.math.BigDecimal; import java.util.*; import java.util.function.Function; import java.util.stream.Collectors; /** * Created with IntelliJ IDEA. * User: Administrator * Date: 2023/1/6/006 * Time: 15:55 * Description: Lambada List集合操作 */ public class test { public static void main(String[] args) { List<Person> persons = new ArrayList<>(); persons.add(new Person(22, "男", 90.0,new BigDecimal(150))); persons.add(new Person(17, "女", 91.0,new BigDecimal(152))); persons.add(new Person(12, "男", 92.0,new BigDecimal(155))); persons.add(new Person(12, "女", 92.0,new BigDecimal(158))); persons.add(new Person(25, "女", 93.0,new BigDecimal(159))); // sortPersons(persons);//排序 // ages(persons);//取某个属性list groupbySex(persons);//按照属性分组 // filterPersons(persons);//过滤集合 // keyMap(persons);//list转map重复key覆盖 // getDataMap(persons);//获取最大最小值及平均数 // sumAge(persons);//获取基本类型的和 // bigDecimalWeightSum(persons);//获取Bigdecimal求和 // distinctAgeList(persons);//对基本集合去重 // countByList(persons);//对集合中相同属性进行计数 // sort(persons);//集合排序 // sorted(persons);//集合排序 // reverseOrder(persons);//倒叙排序 // multiOrder(persons);//多个字段排序 } /** * List排序 * @param persons * @return */ public static List<Person> sortPersons(List<Person> persons){ persons.sort((Person o1, Person o2) -> { return o1.age - o2.age; }); /* Person{age=12, sex=男, score=92.0} Person{age=17, sex=女, score=91.0} Person{age=22, sex=男, score=90.0} Person{age=25, sex=女, score=93.0} */ persons.forEach(System.out::println); return persons; } //取某个属性List public static List<Integer> ages(List<Person> persons){ List<Integer> ages=persons.stream().map(Person::getAge).collect(Collectors.toList()); ages.forEach(System.out::println); return ages; } //按照属性分组 public static Map<String, List<Person>> groupbySex(List<Person> persons){ Map<String, List<Person>> groupbySexs=persons.stream().collect(Collectors.groupingBy(Person::getSex)); //{女=[Person{age=17, sex=女, score=91.0}, Person{age=25, sex=女, score=93.0}], 男=[Person{age=12, sex=男, score=92.0}, Person{age=22, sex=男, score=90.0}]} System.out.println(groupbySexs); return groupbySexs; } //过滤集合 public static List<Person> filterPersons(List<Person> persons){ List<Person> filterPersons=persons.stream().filter(Person->Person.getAge()>=17).collect(Collectors.toList()); //[Person{age=17, sex=女, score=91.0}, Person{age=22, sex=男, score=90.0}, Person{age=25, sex=女, score=93.0}] System.out.println(filterPersons); return filterPersons; } //list转map重复key覆盖 public static Map<Integer,Person> keyMap(List<Person> persons){ Map<Integer,Person> keyPersonMap=persons.stream().collect(Collectors.toMap(Person::getAge, Function.identity(),(key1, key2)->key1)); System.out.println(keyPersonMap); return keyPersonMap; } //获取最大最小值及平均数 public static Map<String,Object> getDataMap(List<Person> persons){ Map<String,Object> dataMap=new HashMap<>(); //最大值 Integer max=persons.stream().mapToInt(Person::getAge).max().getAsInt(); Integer min=persons.stream().mapToInt(Person::getAge).min().getAsInt(); double Average=persons.stream().mapToInt(Person::getAge).average().getAsDouble(); dataMap.put("max",max); dataMap.put("min",min); dataMap.put("Average",Average); System.out.println(dataMap); return dataMap; } //基本类型求和 public static Integer sumAge(List<Person> persons){ Integer sumAge=persons.stream().mapToInt(Person::getAge).sum(); System.out.println("sumAge:"+sumAge); return sumAge; } //bigdecimal求和 public static BigDecimal bigDecimalWeightSum(List<Person> persons){ BigDecimal weightSum=persons.stream().map(Person::getWeight).reduce(BigDecimal.ZERO,BigDecimal::add); System.out.println("weightSum:"+weightSum); return weightSum; } //对基本集合去重 public static List<Integer> distinctAgeList(List<Person> persons){ List<Integer> ages=ages(persons); System.out.println("ages:"+ages); List<Integer> distinctAgeList=ages.stream().distinct().collect(Collectors.toList()); System.out.println("distinctAgeList:"+distinctAgeList); return distinctAgeList; } //判断是否存在某个属性值 public static boolean exist(List<Person> persons){ boolean exist=persons.stream().allMatch(s->s.getAge()==12); System.out.println("exist:"+exist); return exist; } //对集合中相同属性进行计数 public static long countByList(List<Person> persons){ long count=persons.stream().filter(s->s.getAge()==12).count(); System.out.println("count:"+count); return count; } //对集合进行排序 public static List<Person> sort(List<Person> persons){ persons.sort(Comparator.comparing(Person::getAge)); System.out.println("persons-1:"+persons); return persons; } //对集合进行排序 public static List<Person> sorted(List<Person> persons){ persons.stream().sorted(Comparator.comparing(Person::getAge)); System.out.println("persons-2:"+persons); return persons; } //倒序排序 public static List<Person> reverseOrder(List<Person> persons){ persons.sort(Comparator.comparing(Person::getAge,Comparator.reverseOrder())); System.out.println("persons-rever:"+persons); return persons; } //多个字段排序 public static List<Person> multiOrder(List<Person> persons){ persons.sort(Comparator.comparing(Person::getAge,Comparator.reverseOrder()).thenComparing(Person::getWeight)); System.out.println("persons:"+persons); return persons; } }