一、类定义
package com.xxx;import java.math.BigDecimal;public class Student {private String name;private Integer age;private Boolean gender;private Double score;private BigDecimal money;public Student() {super();}public Student(String name, Integer age, Boolean gender, Double score, BigDecimal money) {this.name = name;this.age = age;this.gender = gender;this.score = score;this.money = money;}@Overridepublic String toString() {return "[name=" + this.name + ", age=" + this.age + ", gender=" + (gender ? "男" : "女") + ", score=" + this.score + ", money=" + this.money + "]";}public String getName() {return name;}public Student setName(String name) {this.name = name;return this;}public Integer getAge() {return age;}public Student setAge(Integer age) {this.age = age;return this;}public Boolean getGender() {return gender;}public Student setGender(Boolean gender) {this.gender = gender;return this;}public Double getScore() {return score;}public void setScore(Double score) {this.score = score;}public BigDecimal getMoney() {return money;}public void setMoney(BigDecimal money) {this.money = money;}}
二、工具类
package com.xxx;import java.util.List;import java.util.Map;import java.util.Set;/*** 数据处理工具类* * @Author LIUYINGDI* @Date: -09-06*/public class DataHandler {private static final DataHandler SINGLE = new DataHandler();private DataHandler() {super();}public static DataHandler getInstance() {return SINGLE;}/*** 将集合转为字符串*/public <T> String convertList2String(List<T> list, String separator, String prefix, String suffix) {String result = "";if (list != null && list.size() > 0) {result = prefix + list.get(0).toString() + suffix;for (int index = 1; index < list.size(); index++) {result = result + separator + prefix + list.get(index).toString() + suffix;}}return result;}/*** 将Map转为String*/public <T1, T2> String convertMap2String(Map<T1, T2> map, String separator, String prefix, String suffix) {String result = "";if (map != null && map.size() > 0) {Set<T1> keySet = map.keySet();int index = 0;for (T1 key : keySet) {T2 value = map.get(key);if (index == 0) {result = prefix + key.toString() + ":" + value.toString() + suffix;index++;} else {result = result + separator + prefix + key.toString() + ":" + value.toString() + suffix;}}}return result;}}
三、lambda表达式常见用法
package com.xxx;import java.math.BigDecimal;import java.util.ArrayList;import parator;import java.util.List;import java.util.Map;import java.util.stream.Collectors;/*** lambda表达式* * @Author LIUYINGDI* @Date: -12-03*/public class Test {private static List<Student> studentList;static {studentList = new ArrayList<Student>();studentList.add(new Student("WangShuang", 24, false, 91.5, new BigDecimal(30.01)));studentList.add(new Student("ZhaoLiNa", 21, false, 65.0, new BigDecimal(10.02)));studentList.add(new Student("WuLei", 26, true, 85.0, new BigDecimal(200.03)));studentList.add(new Student("Aguero", 31, true, 60.0, new BigDecimal(7500.04)));studentList.add(new Student("Silva", 34, true, 60.0, new BigDecimal(1500.05)));studentList.add(new Student("Pogba", 26, true, 59.0, new BigDecimal(9000.06)));}private static DataHandler dataHandler = DataHandler.getInstance();public static void main(String[] args) {/* 0. 数据准备 */System.out.println("\n========== 0 ============================");System.out.println(studentList.size());/* 1. lambda表达式：List<Object> --> List<String> */System.out.println("\n========== 1 ============================");List<String> nameList = studentList.stream().map(t -> t.getName()).collect(Collectors.toList());System.out.println(dataHandler.convertList2String(nameList, "、", "<", ">"));List<Integer> ageList = studentList.stream().map(t -> t.getAge()).collect(Collectors.toList());System.out.println(dataHandler.convertList2String(ageList, "、", "<", ">"));/* 2. lambda表达式：List<Object> --> Map<String, Object> */System.out.println("\n========== 2 ============================");Map<String, Student> map1 = studentList.stream().collect(Collectors.toMap(Student::getName, t -> t));System.out.println(dataHandler.convertMap2String(map1, "、", "<", ">"));/* 注：当key重复时会报错，因此常用于：List<Object> --> Map<ID/UUID, Object>。以下为报错代码 */// Map<Integer, Person> map2 = personList.stream().collect(Collectors.toMap(Person::getAge, t -> t));// System.out.println(dataHandler.convertMap2String(map2, "、", "<", ">"));/* 3.1 lambda表达式：对Integer字段求和 */System.out.println("\n========== 3.1 ============================");Integer ageSummation = studentList.stream().mapToInt(Student::getAge).sum();System.out.println((24 + 21 + 26 + 31 + 34 + 26) + ", " + ageSummation);/* 3.2 lambda表达式：对BigDecimal字段求和 */System.out.println("\n========== 3.2 ============================");BigDecimal moneySummation = studentList.stream().map(Student::getMoney).reduce(BigDecimal.ZERO, BigDecimal::add);System.out.println((30.01 + 10.02 + 200.03 + 7500.04 + 1500.05 + 9000.06) + ", " + moneySummation);/* 4. lambda表达式：对指定字段进行过滤 */System.out.println("\n========== 4 ============================");List<Student> highScoreStudentList = studentList.stream().filter(t -> t.getScore() >= 60).collect(Collectors.toList());List<String> highScoreNameList = highScoreStudentList.stream().map(t -> t.getName()).collect(Collectors.toList());System.out.println(dataHandler.convertList2String(highScoreNameList, "、", "<", ">"));/* 5. lambda表达式：以指定字段为Key进行分组 List<Object> --> Map<String, List<Object>> */System.out.println("\n========== 5 ============================");Map<Boolean, List<Student>> ageGroupMap = studentList.stream().collect(Collectors.groupingBy(Student::getGender));System.out.println("男" + ageGroupMap.get(true).size() + "人, 女" + ageGroupMap.get(false).size() + "人");/* 6. lambda表达式：排序 ASC - 但此种排序方式，一旦score=NULL，则会抛出空指针异常 */System.out.println("\n========== 6 ============================");studentList.sort(paring(Student::getScore));List<String> ascSortNameList = studentList.stream().map(t -> t.getName()).collect(Collectors.toList());System.out.println(dataHandler.convertList2String(ascSortNameList, "、", "<", ">"));List<Double> ascSortMoneyList = studentList.stream().map(t -> t.getScore()).collect(Collectors.toList());System.out.println(dataHandler.convertList2String(ascSortMoneyList, "、", "<", ">"));/* 6.1 lambda表达式：排序 ASC - score=NULL的对象排在前面 */System.out.println("\n========== 6.1 ============================");studentList.add(new Student("XXX", 0, true, null, null));studentList.sort(paring(Student::getScore, Comparator.nullsFirst(Comparator.naturalOrder())));ascSortNameList = studentList.stream().map(t -> t.getName()).collect(Collectors.toList());System.out.println(dataHandler.convertList2String(ascSortNameList, "、", "<", ">"));/* 6.2 lambda表达式：排序 ASC - score=NULL的对象排在后面 */System.out.println("\n========== 6.2 ============================");studentList.sort(paring(Student::getScore, Comparator.nullsLast(Comparator.naturalOrder())));ascSortNameList = studentList.stream().map(t -> t.getName()).collect(Collectors.toList());System.out.println(dataHandler.convertList2String(ascSortNameList, "、", "<", ">"));/* 7. lambda表达式：以指定字段进行删除 */System.out.println("\n========== 7 ============================");studentList.removeIf(t -> t.getScore() == null);nameList = studentList.stream().map(t -> t.getName()).collect(Collectors.toList());System.out.println(dataHandler.convertList2String(nameList, "、", "<", ">"));/* 8. lambda表达式：排序 DESC - 但此种排序方式，一旦score=NULL，则会抛出空指针异常；处理null值的方式与ASC同理 */System.out.println("\n========== 8 ============================");studentList.sort(paring(Student::getScore, Comparator.reverseOrder()));List<String> descSortNameList = studentList.stream().map(t -> t.getName()).collect(Collectors.toList());System.out.println(dataHandler.convertList2String(descSortNameList, "、", "<", ">"));List<Double> descSortMoneyList = studentList.stream().map(t -> t.getScore()).collect(Collectors.toList());System.out.println(dataHandler.convertList2String(descSortMoneyList, "、", "<", ">"));}}
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