Get all variable names in a class

Question

I have a class and I want to find all of its public fields (not methods). How can I do this?

• Crozin: You should be able to do this using Reflection API.

Answer 1

Field[] fields = YourClassName.class.getFields();

returns an array of all public variables of the class.

getFields() return the fields in the whole class-heirarcy. If you want to have the fields defined only in the class in question, and not its superclasses, use getDeclaredFields(), and filter the public ones with the following Modifier approach:

Modifier.isPublic(field.getModifiers());

The YourClassName.class literal actually represents an object of type java.lang.Class. Check its docs for more interesting reflection methods.

The Field class above is java.lang.reflect.Field. You may take a look at the whole java.lang.reflect package.

• Dany Y: is this solution slow ? or can we use it freely ?
• Bozho: it's ok. But don't overuse it.

Answer 2

https://docs.oracle.com/javase/tutorial/reflect/class/classMembers.html also has charts for locating methods and constructors.

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Answer 3

You can use any of the two based on your need:

Field[] fields = ClassName.class.getFields(); // returns inherited members but not private members.
Field[] fields = ClassName.class.getDeclaredFields(); // returns all members including private members but not inherited members.

To filter only the public fields from the above list (based on requirement) use below code:

List<Field> fieldList = Arrays.asList(fields).stream().filter(field -> Modifier.isPublic(field.getModifiers())).collect(
 Collectors.toList());

Answer 4

As mentioned by few users, below code can help find all the fields in a given class.

TestClass testObject= new TestClass().getClass();
Method[] methods = testObject.getMethods();
for (Method method:methods)
{
 String name=method.getName();
 if(name.startsWith("get"))
 {
 System.out.println(name.substring(3));
 }else if(name.startsWith("is"))
 {
 System.out.println(name.substring(2));
 }
}

However a more interesting approach is below:

With the help of Jackson library, I was able to find all class properties of type String/integer/double, and respective values in a Map class. (without using reflections api!)

TestClass testObject = new TestClass();
com.fasterxml.jackson.databind.ObjectMapper m = new com.fasterxml.jackson.databind.ObjectMapper();
Map<String,Object> props = m.convertValue(testObject, Map.class);
for(Map.Entry<String, Object> entry : props.entrySet()){
 if(entry.getValue() instanceof String || entry.getValue() instanceof Integer || entry.getValue() instanceof Double){
 System.out.println(entry.getKey() + "-->" + entry.getValue());
 }
}

• RukaDo: Doesn't Jackson use reflection? Correct me if I am wrong

Answer 5

List fields=Arrays.stream(reservation.class.getDeclaredFields()).map(Field::getName).toList();

It returns the list of all members declared inside a class including the private members.