Java Reflection - Java Field Reflection

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We can use java.lang.reflect.Field class to get information about a field in a class.

The following four methods in the Class class can return Field object about the fields.

Field[] getFields()
Field[] getDeclaredFields()
Field getField(String name)
Field getDeclaredField(String name)

The getFields() method returns all the accessible public fields declared in the class or inherited from the superclass.

The getDeclaredFields() method returns all the fields that appear in the declaration of the class only(not from inherited fields).

getField(String name) and getDeclaredField(String name) get the Field object by the field name.

Example

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
/*  w ww. ja  v  a 2s .c o m*/
class MySuperClass {
  public int super_id = -1;
  public String super_name = "Unknown";

}

class MyClass extends MySuperClass{
  public int id = -1;
  public String name = "Unknown";

}

public class Main {
  public static void main(String[] args) {
    Class<MyClass> c = MyClass.class;

    // Print declared fields
    ArrayList<String> fieldsDesciption = getDeclaredFieldsList(c);

    System.out.println("Declared Fields for " + c.getName());
    for (String desc : fieldsDesciption) {
      System.out.println(desc);
    }
    fieldsDesciption = getFieldsList(c);

    System.out.println("\nAccessible Fields for " + c.getName());
    for (String desc : fieldsDesciption) {
      System.out.println(desc);
    }
  }

  public static ArrayList<String> getFieldsList(Class c) {
    Field[] fields = c.getFields();
    ArrayList<String> fieldsList = getFieldsDesciption(fields);
    return fieldsList;
  }

  public static ArrayList<String> getDeclaredFieldsList(Class c) {
    Field[] fields = c.getDeclaredFields();
    ArrayList<String> fieldsList = getFieldsDesciption(fields);
    return fieldsList;
  }

  public static ArrayList<String> getFieldsDesciption(Field[] fields) {
    ArrayList<String> fieldList = new ArrayList<>();

    for (Field f : fields) {
      int mod = f.getModifiers() & Modifier.fieldModifiers();
      String modifiers = Modifier.toString(mod);

      Class<?> type = f.getType();
      String typeName = type.getSimpleName();

      String fieldName = f.getName();

      fieldList.add(modifiers + "  " + typeName + "  " + fieldName);
    }

    return fieldList;
  }
}

The code above generates the following result.

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