dynamic filtering of java object

Question

I have following java object

Obj:
----
String id;
List<A>;

A:
--
String A_ID;
String A_PROPERTY;

What I am looking for is to be able to search in a given object. ex: search in a list where A.A_ID = 123

I need to dynamically pass

A_ID = 123

and it would give me

A_Property

I know I could search through a list through iterator, but is there already frameworks out there which lets you do this?

thanks

Answer 1

Something like Quaere. From their site:

Quaere is an open source, extensible framework that adds a querying syntax reminiscent of SQL to Java applications. Quaere allows you to filter, enumerate and create projections over a number of collections and other queryable resources using a common, expressive syntax.

Answer 2

why do you need a framework? how about

public String lookupPropertyById(String id)
{
    for (A a : myList)
    {
        if (id.equals(a.id))
            return a.property;
    }
    return null;   // not found
}

Answer 3

Hashmap if you only search by one property which has the same type for every inputed object. For example, a string. The object 1 has the string "Obj1" for key and the second object has the string "Test2" for key. When you use the get method with the parameter "Obj1", it will return the first object. P.S. It's really hard to read your "pseudo-code".

Answer 4

Using a hashmap.

Map<String,A> map = new HashMap<String,A>();

A a = new A();
a.id = "123";
a.property="Hello there!";

map.put( a.id , a );

Later

map.get( "123"); // would return the instance of A and then a.property will return "Hello there!"

Answer 5

lambdaj is a very nice library for Java 5.

For example:

Person me = new Person("Mario", "Fusco", 35);
Person luca = new Person("Luca", "Marrocco", 29);
Person biagio = new Person("Biagio", "Beatrice", 39);
Person celestino = new Person("Celestino", "Bellone", 29);
List<Person> people = asList(me, luca, biagio, celestino);

it is possible to filter the ones having more than 30 years applying the following filter:

List<Person> over30 = filter(having(on(Person.class).getAge(), greaterThan(30)), people);