Question

is it possible to get an object from his reference id?

i get a list of String containing the reference id of an object like:

com.test.test.business.model.Gamma@20

how to get the object from this reference id?

it’s only a string and it isn’t castable to the object itself

Answer 1

What you see is called the default toString of an object. It is an amalgamation of the FQCN (fully qualified class name) of the class it belongs to and the hashCode of the object.

Quoting from the JavaDoc of toString:

The toString method for class Object returns a string consisting of
the name of the class of which the object is an instance, the at-sign
character `@’, and the unsigned hexadecimal representation of the hash
code of the object. In other words, this method returns a string equal
to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())

In short, you can’t get an object using this reference id.

We can override toString to give a more human readable output. Take a look at the below two classes, with and without toString. Try to execute the main method and compare the output of the two print statements.

class Person {
    private String name;

    @Override
    public String toString() {
        return "Person [name=" + this.name + "]";
    }
}

class Address {
    private String town;
}

public class Test {
    public static void main(String... args) {
        Person person = new Person();
        Address address = new Address();

        System.out.println("Person is : " + person);
        System.out.println("Address is : " + address);
    }
}

However, if you are really looking for a way to persist objects and resurrect them at a later stage, you should read up on Serialization.