Java8 使用 stream().map()提取List对象的某一列值及排重

Java8 使用 stream().map()提取List对象的某一列值及排重

 

List对象类（StudentInfo）

public class StudentInfo implements Comparable<StudentInfo> {

//名称
private String name;

//性别 true男 false女
private Boolean gender;

//年龄
private Integer age;

//身高
private Double height;

//出生日期
private LocalDate birthday;

public StudentInfo(String name, Boolean gender, Integer age, Double height, LocalDate birthday){
this.name = name;
this.gender = gender;
this.age = age;
this.height = height;
this.birthday = birthday;
}

public String toString(){
String info = String.format("%s %s %s %s %s",this.name,this.gender.toString(),this.age.toString(),this.height.toString(),birthday.toString());
return info;
}

public static void printStudents(List<StudentInfo> studentInfos){
System.out.println("[姓名] [性别] [年龄] [身高] [生日]");
System.out.println("----------------------------------------------------------");
studentInfos.forEach(s->System.out.println(s.toString()));
System.out.println(" ");
}

@Override
public int compareTo(StudentInfo ob) {
return this.age.compareTo(ob.getAge());
//return 1;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Boolean getGender() {
return gender;
}

public void setGender(Boolean gender) {
this.gender = gender;
}

public Integer getAge() {
return age;
}

public void setAge(Integer age) {
this.age = age;
}

public Double getHeight() {
return height;
}

public void setHeight(Double height) {
this.height = height;
}

public LocalDate getBirthday() {
return birthday;
}

public void setBirthday(LocalDate birthday) {
this.birthday = birthday;
}
}

StudentInfo对象类

测试数据

//测试数据，请不要纠结数据的严谨性
List<StudentInfo> studentList = new ArrayList<>();
studentList.add(new StudentInfo("李小明",true,18,1.76,LocalDate.of(2001,3,23)));
studentList.add(new StudentInfo("张小丽",false,18,1.61,LocalDate.of(2001,6,3)));
studentList.add(new StudentInfo("王大朋",true,19,1.82,LocalDate.of(2000,3,11)));
studentList.add(new StudentInfo("陈小跑",false,17,1.67,LocalDate.of(2002,10,18)));

提取某一列（以name为例）

 //输出List
StudentInfo.printStudents(studentList);
//从对象列表中提取一列(以name为例)
List<String> nameList = studentList.stream().map(StudentInfo::getName).collect(Collectors.toList());
//提取后输出name
nameList.forEach(s-> System.out.println(s));

输出结果如下图：

 提取age列并排重（使用distinct()函数）

//提取前输出
StudentInfo.printStudents(studentList);
//从对象列表中提取age并排重
List<Integer> ageList = studentList.stream().map(StudentInfo::getAge).distinct().collect(Collectors.toList());
ageList.forEach(a-> System.out.println(a));

结果如下图：