I'm looking for a way to get all public attributes in the class and all subclasses of an object (name of the attribute and its value). Let say we have a People object:
i
mport java.util.ArrayList;
public class People {
public ArrayList<Person> ppl= new ArrayList<Person>();
int count=2;
public People() {
ppl.add(new Person(55, "Daddy", "Long Legs"));
ppl.add(new Person(20, "Jhon", "Snow"));
}
public class Person{
public int age;
public Name name;
public Person(int age, String first, String last){
this.name = new Name(first, last);
this.age = age;
}
public class Name{
String first;
String last;
public Name(String first, String last) {
this.first = first;
this.last = last;
}
}
}
}
I saw a reference here (I can't comment on there bc I don't have enough points): Java reflection get sub class variable values / get object instance from member field
and tried to implement it also but then my output is
ppl [People$Person@4aa298b7, People$Person@7d4991ad]
whereas I need it needs to go into each Person and extract its variables(and their values). I searched for a information that could help me but I couldn't find anything..any advice?
toString()
method What you are getting People$Person@4aa298b7
is the Object.toString
representation....
getClass().getName() + '@' + Integer.toHexString(hashCode())
IMHO You need to override the toString()
method in both classes: Person
and Name
.
For example:
public class Name{
String first;
String last;
public Name(String first, String last) {
this.first = first;
this.last = last;
}
@Override
public String toString() {
return this.first + " " + this.last;
}
}
Person
class If this does not fit, you can get fields names and values using reflection like this:
public static void main(String[] args) throws IllegalAccessException
{
People pe = new People();
Field[] allFields = People.Person.class.getDeclaredFields();
for (Field field : allFields)
{
for (People.Person p : pe.ppl)
System.out.println("Name: " + field.getName() + ". Value: " + field.get(p));
}
}
OUTPUT:
Name: age. Value: 55
Name: age. Value: 20
Name: name. Value: Daddy Long Legs
Name: name. Value: Jhon Snow
Name: this$0. Value: People@677327b6
Name: this$0. Value: People@677327b6
NOTE: if you don't want this 2 final values representing the People with ugly results you can:
Person
and Name
and make them 2 independent classes toString()
method in People
class If you want to dynamically get fields from inner classes:
public static void main(String[] args) throws IllegalAccessException
{
Class[] allClasses = People.class.getClasses();
for (Class clazz : allClasses) {
Field[] allFields = clazz.getFields();
for (Field field : allFields) {
String className = clazz.getName();
String fieldName = field.getName();
System.out.println("Class name: " + className + " - Field name: " + fieldName + ".");
}
}
}
OUTPUT:
Class name: People$Name - Field name: first.
Class name: People$Name - Field name: last.
Class name: People$Person - Field name: age.
Class name: People$Person - Field name: name.
But not sure how you can get values from inside the ArrayList<Person>
....
public People() {
ppl.add(new Person(55, "Daddy", "Long Legs"));
ppl.add(new Person(20, "Jhon", "Snow"));
for (Person person : ppl) {
System.out.println(person.name.last);
System.out.println(person.name.first);
System.out.println(person.age);
}
System.out.println("Size of list: " + ppl.size());
}
Example without toString() method.
I believe the closest you can get is related to this question java: get all variable names in a class .
Using Field[] fields = YourClassName.class.getFields();
returns all class fields as java.lang.reflect.Field .
You can check if field is public using Field.getModifiers() and Modifier.isPublic(Modifier) .
You can get the field value using Object Field.get() .
Hope that helps.
I Agree with @Jordi Castilla , you need to override toString method properly to get correct output.
For Example :
import java.util.ArrayList;
class People {
public ArrayList<Person> ppl= new ArrayList<Person>();
int count=2;
public People() {
ppl.add(new Person(55, "Daddy", "Long Legs"));
ppl.add(new Person(20, "Jhon", "Snow"));
}
@Override
public String toString() {
return "{ Count: "+this.count + " , People:" + this.ppl+" }";
}
public class Person{
public int age;
public Name name;
public Person(int age, String first, String last){
this.name = new Name(first, last);
this.age = age;
}
@Override
public String toString() {
return "{ Name: "+this.name + " , Age:" + this.age+" }";
}
public class Name{
String first;
String last;
public Name(String first, String last) {
this.first = first;
this.last = last;
}
@Override
public String toString() {
return "{ FirstName: "+this.first + ", LastName: " + this.last+ " }";
}
}
}
public static void main(String[] args) {
People ppl = new People();
System.out.println("OUTPUT => "+ ppl.toString());
}
}
//Output
OUTPUT => {
Count: 2 ,
People:[
{ Name: { FirstName: Daddy, LastName: Long Legs } , Age:55 },
{ Name: { FirstName: Jhon, LastName: Snow } , Age:20 }
]
}
here is a recursive method I did (after I added a toString method to Name class). Here it is. However, it is still doesn't prints the variable names inside the ppl list:
private static String getAllFields(Object obj){
Class<?> objClass = obj.getClass();
StringBuilder res = new StringBuilder();
Field[] fields = objClass.getFields();
res.append(objClass+"\n");
for(Field field : fields) {
Class<?> type = field.getType();
String name = field.getName();
res.append(" name: "+name+ " ");
try {
Object value = field.get(obj);
res.append("value: "+value+ "\n");
if (!type.isPrimitive() && !name.contains("java.lang"))
{
res.append(getAllFields(value));
}
} catch (IllegalArgumentException | IllegalAccessException e) {
e.printStackTrace();
}
}
return res.toString();
}
here is the output: class People name: ppl value: [Daddy Long Legs 55 , Jhon Snow 20 ] class java.util.ArrayList name: count value: 2
notice that there isn't the Person class name there in the output or the names of the variable names of the variables there. I don't really understand why
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