Persistent data structures in Java

Question

Does anyone know a library or some at least some research on creating and using persistent data structures in Java? I don\'t refer to persistence as long term storage but persis

Answer 1

Follow a very simple tentative with dynamic proxy:

class ImmutableBuilder {

    static  T of(Immutable immutable) {
        Class targetClass = immutable.getTargetClass();
        return (T) Proxy.newProxyInstance(targetClass.getClassLoader(),
            new Class[]{targetClass},
            immutable);
    }

    public static  T of(Class aClass) {
        return of(new Immutable(aClass, new HashMap()));
    }
}

class Immutable implements InvocationHandler {

    private final Class targetClass;
    private final Map fields;

    public Immutable(Class aTargetClass, Map immutableFields) {
        targetClass = aTargetClass;
        fields = immutableFields;
    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (method.getName().equals("toString")) { 
            // XXX: toString() result can be cached
            return fields.toString();
        }

        if (method.getName().equals("hashCode")) { 
            // XXX: hashCode() result can be cached
            return fields.hashCode();
        }

        // XXX: naming policy here
        String fieldName = method.getName(); 

        if (method.getReturnType().equals(targetClass)) {
          Map newFields = new HashMap(fields);
          newFields.put(fieldName, args[0]);
          return ImmutableBuilder.of(new Immutable(targetClass, newFields));
        } else {
            return fields.get(fieldName);
        }
    }

    public Class getTargetClass() {
        return targetClass;
    }
}

usage:

interface Person {
    String name();
    Person name(String name);
    int age();
    Person age(int age);
}

public class Main {

    public static void main(String[] args) {
        Person mark = ImmutableBuilder.of(Person.class).name("mark").age(32);
        Person john = mark.name("john").age(24);
        System.out.println(mark);
        System.out.println(john);
    }
}

grow directions:

• naming policy (getName, withName, name)
• caching toString(), hashCode()
• equals() implementations should be straightforward (although not implemented)

hope it helps :)