Try this, it requires Java 8.
Just copy and save the file into Stateful.java.
It is available here as well:
https://bitbucket.org/momomo/opensource/src/e699d8da450897b5f6cd94a5d329b3829282d1d6/src/momomo/com/Stateful/Stateful.java?at=default
/**************************************************************************************************************************************
* Copyright(C) 2014, Mo Enterprises Inc. *
* All rights reserved. *
* Mo Enterprises Inc Opensource License 'MoL1'. *
* *
* (1) Use of this source code, wether identical, changed or altered is allowed, for both commercial and non-commercial use. *
* *
* (2) This source code may be changed and altered freely to be used only within your entity/organisation, given that a notice of all *
* changes introduced are listed and included at the end of a copy of this exact copyright notice, including the name and date of *
* the entity/organization that introduced them. *
* *
* (3) The redistribution or publication to the public of this source code, if changed or altered, is striclty prohibited using any *
* medium not owned, and/or controlled by Mo Enterprises Inc unless a written consent has been requested and recieved by *
* representatives of Mo Enterprises Inc. *
* *
* (4) The distribution of any work to the public derived through the use of this source code, wether identical, changed or altered, *
* is allowed, as long as it in full compliance of (3). *
* *
* (5) Mo Enterprises Inc considers the techniques and design patterns employed in this source code as unique and making the *
* redistribution of this source code with altered names, and/or a rearrangement of code as a severe breach of the copyright law *
* and this license. Mo Enterprises Inc reserves all rights to puruse any and all legal options. *
* *
* (6) All copies of this source code, wether identical, changed/altered must include this entire copyright notice, list all changes *
* made including the name and date of the entity/organization that introduced them, as wel as the following disclaimer: *
* *
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND *
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED *
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE *
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR *
* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES *
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; *
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND *
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT *
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS *
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. *
* *
* Please contact us on opensource@{at}momomo.com if you have an improvement to this source code you'd like to contribute. *
* We'll make sure to include your name and/or organisation as a contributor if accepted. *
**************************************************************************************************************************************/
import java.util.IdentityHashMap;
import java.util.Map;
/**
* @Author Mo. Joseph
*
* Consider memory leakage usage.
* None of the public methods below should be used outside of the interface extending Stateful!
*/
@SuppressWarnings("unchecked")
public interface Stateful {
/**
* @Private access only! Strict enforcement, otherwise risks for memomry leaks!
*/
static final Map<Stateful, IdentityHashMap<Class<State>, State>> STATES = new WeakIdentityHashMap<>( );
/**
* @Protected access only! Strict enforcement, otherwise risks for memomry leaks!
*
* Note, this method can not be generified!
* If so, then it will conflict when a class implements several Stateful interfaces.
*/
default <Y extends Stateful, T extends State<Y>> T $(Class<T> clazz) {
synchronized (this) {
IdentityHashMap<Class<State>, State> map = STATES.get(this);
if ( map == null ) {
STATES.put(this, map = new IdentityHashMap<>() );
}
State state = map.get(clazz);
if (state == null) {
try {
map.put(cast(clazz), state = clazz.newInstance() );
} catch (Throwable e) {
throw new RuntimeException(e);
}
}
return (T) state;
}
}
/**
* @Protected access only! Strict enforcement, otherwise risks for memomry leaks!
* May only be extended from within an interface that implements Stateful.
*/
static interface State<Y extends Stateful> {}
/**
* @Private
* Util method for casting used here. Simple casting won't work for some reason.
*/
static <T>T cast(Object obj){
return (T) obj;
}
/*******************************************************************************
* Example code below:
*******************************************************************************/
public static void main(String[] args) {
Person mo = new Person();
mo.setName("Mo. Joseph");
mo.setStreet("Mansion Street 1");
System.out.println(mo.getName());
System.out.println(mo.getStreet());
Pet garfield = new Pet ();
garfield.setName("Garfield");
System.out.println(garfield.getName());
Person santa = new Person();
santa.setName("Santa");
santa.setStreet("North Pole Street 1");
System.out.println(santa.getName());
System.out.println(santa.getStreet());
mo.setName("mo");
System.out.println(mo.getName());
System.out.println(santa.getName());
System.out.println(garfield.getName());
System.out.println(santa.getStreet());
}
public static class Person implements Named, Address {
}
public static class Pet implements Named {
}
public static interface Named extends Stateful {
static class State implements Stateful.State<Named> {
private String name;
}
public default void setName(String name) {
$(State.class).name = name;
}
public default String getName() {
return $(State.class).name;
}
}
public static interface Address extends Stateful {
static class State implements Stateful.State<Address> {
private String street;
}
public default void setStreet(String street) {
$(State.class).street = street;
}
public default String getStreet() {
return $(State.class).street;
}
}
/************************************************************************************/
}
