CODEWITHSUNDEEP
javaclassclass-attributes
PЯӨGЯΛMMΣЯ
PЯӨGЯΛMMΣЯ

Reputation: 405

Android Java, How to get the value of class attribute?

I want to get the value a class attribute, But I am getting exception : java.lang.NoSuchFieldException

Person.class

public class Person {

    public static final String name = "person name";

}

MainActivity.class

...

private void method() {

    Class myClass = Person.class;

    String name = myClass.getField("name");

}

...

I am getting a java.lang.NoSuchFieldException exception for the getField method.

I tried these solutions but with no avail ...

  1. Change getField method to getDeclaredField

  2. Surround the code by try/catch, and got another error (Incompatible types : java.lang.String and java.lang.reflect.Field)

  3. Invalidate Android Studio caches and restart

I don't Know how to access this value, Any solutions or suggestions are welcomed.

Thanks in advance.

Upvotes: 1

Views: 2877

Answers (5)

user12465043
user12465043

Reputation:

It's a static constant. Static means there is only one value at a time possible. Or say it like this: The class attribute 'name' is a class attribute, not an object attribute! The attribute belongs to the class!

So you don't need to create an instance of your Person class.

You just can use:

String name = Person.name;

Remember: this only works cause the name belongs to the class. And it does so, because you declared your name variable static.

Upvotes: 0

Adrian Efford
Adrian Efford

Reputation: 483

  1. If your variable in the class "Person" is static:
    (This is not the best solution in my opinion)

    Explanation: getField method returns a type "field" so you CAN NOT save into a variable from another type without a conversion.
    YourField.get returns an object so you CAN NOT save into a variable from another type without a conversion.
try{
    Class _person = Person.class;
    Field field = _person.getField("name");
    Object value = field.get(null);
    String valueString = (String)value; /*The String you are looking for*/
}catch (Exception e) {
    //TODO handle exception
}
  1. If your variable in the class "Person" is static:
    String valueString = Person.name /*The value you are looking for*/
  1. If your variable isn't static but public:
    IMPORTANT (If you have not set a default value to the variable):
    In this case the value will be an empty string because you are creating a new instance of your calss. You can set the "person name" in the constructor of your Person class another way you will get an empty string because the variable isn't static.
    Person _person = new Person();
    String personName = _person.name;

Upvotes: 1

Christilyn Arjona
Christilyn Arjona

Reputation: 2283

If you want to access the value of the field, you can use the get(...) method with a null argument - since it's a static field, it does not require any instance:

private void method() {

    Class myClass = Person.class;

    Field field = myClass.getField("name");
    String name = field.get(null);

    Log.d("Test", "field value: " + name);
}

In your case, it doesn't matter whether you use getField(...) or getDeclaredField(...). You would want to use the latter if you want to grab a field in its superclass or an interface implemented by your class.

For example, if Person were to extend from a class that has a field named sample, you would need to use getDeclaredField("sample") instead.

Upvotes: 1

Yec8789
Yec8789

Reputation: 51

Since that's a constant you declared, access it directly with the class name as below,

String name = Person.name;

Upvotes: 0

Ali Faris
Ali Faris

Reputation: 18610

Change getField method to getDeclaredField

Surround the code by try/catch, and got another error (Incompatible types : java.lang.String and java.lang.reflect.Field)

that because getDeclaredField will return object of type Field not String, just change your code to this

Field field = myClass.getDeclaredField("name");
//do something with field

Upvotes: 1

Related Questions