Getting array of Field Names of a class

Question

I want to get array of field names in the User class. eg name,age.

I tried following code -

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Arrays;


public class Test {

    public static void main(String[] args) {
          Field[] fields = User.class.getDeclaredFields();
          ArrayList<Field> utilList = new ArrayList<Field>(Arrays.asList(fields));
           System.out.println(utilList);
    }
}

class User{
    String name;
    int age;
}

But it is printing [java.lang.String prac1.User.name, int prac1.User.age] .

I need to print [name,age] with square bracket Without looping through it.

Square brackets can be attached after and before, but that is not the way I need it.It should come on its own.

Is it possible somehow using overriding toString methods?

Answer 1

遍历utilList和调用Field.getName在每个项目上。

Answer 2

If you are using Java 8 then you can exploit the Functional features to map a list to a new list using aa map function :

List<String> mapped = utilList.stream().map(field -> field.getName()).collect(Collectors.toList());  

or

String[] mapped = utilList.stream().map(field -> field.getName()).toArray();

check this for more information ,this tutorial may help you also.

Answer 3

ArrayList<String> utilList = new ArrayList<String>();
for (Field field: fields) {
  utilList.add(field.getName());
}

But I don't see the point of using utilList…

Answer 4

You can use the getName method of Field .

Field[] fields = User.class.getDeclaredFields();
for (Field f: fields) {
    System.out.println(f.getName());
}

Output

name
age

Answer 5

It should be something like

Class klass = User.class;
List<String> fieldNames = new ArrayList<String>();
for(Field field: klass.getDeclaredFields()) {
    fieldNames.add(field.getName());
}
System.out.println(fieldNames);

Answer 6

A solution using Regular Expressions, for reference:

// Class
private static final Pattern FIELD_PATTERN =
    Pattern.compile("(?:[\\dA-Za-z\\.]+) (?:[\\dA-Za-z\\.]+)?\\.([A-Za-z]+)");

// Method
{
    // ...
    Matcher matcher=FIELD_PATTERN.matcher(utilList.toString());
    while(matcher.find())
        System.out.println(matcher.replaceAll("$1"));
}

You get:

[name, age]

See the regex explanation and try the code demo .

Oh, and you can build a one-liner out of this:

System.out.println(User.class.getDeclaredFields().toString().replaceAll("(?:[\\dA-Za-z\\.]+) (?:[\\dA-Za-z\\.]+)?\\.([A-Za-z]+)", "$1"));