Embed Mixin in Java?

Question

Using Java 6, how can I implement mixin? It is very easy and affordable in Ruby. How can I get similar in Java?

Answer 1

You can use CGLIB . The Mixin class is able to generate a dynamic class from several delegates of interfaces / objects:

static Mixin create(java.lang.Class[] interfaces, java.lang.Object[] delegates) static Mixin create(java.lang.Object[] delegates) static Mixin createBean(java.lang.Object[] beans) 

Answer 2

I would say just using the composition of the object. Each time you want to add new functionality, make another object in the class as a member. If you want to create all your mixed classes of the same type, you can use the array as a member object, where each element consists of all the others, and you can send it to a specific element.

Answer 3

Since Java only supports one inheritance, this is not possible. Check out WP: Mixin .

EDIT : due to comments about interfaces: the great thing about mixins is that you can combine them without writing combination code. With interfaces, you must implement combinational functionality yourself (except for one class that you can extend)

Answer 4

The easiest way is to use static imports. This allows code reuse that "looks" like part of a class, but is really defined elsewhere.

Pros:

• very simple
• you can "mix" as many static imports as you like

Minuses:

• static methods will not have access until 'this', so you have to go through it manually
• no state: your static methods cannot have their own instance fields. They can only define their own static fields, which are then shared by any object that invokes the static method.
• cannot define public methods in the client class (the one in which it mixes with the code). In Ruby, a mixin import will actually define these public methods as public methods in your class. In Java, inheritance would be the best solution in this case (unless you need to extend multiple classes)

Example:

 import static my.package.MyHelperUtility.methodDefinedInAnotherClass; public class MyNormalCode { public void example() { methodDefinedInAnotherClass(); } } 

Answer 5

I know the question Java 6 said, but in Java 8 we will have a pretty decent alternative: default methods .

We can add “standard” implementations of the interface methods, so we can add new methods without breaking each class that implements the interface.

As long as your mixin is not needed, you can write code in the interface. Then your class can implement as many interfaces as it wants and boom, you have mixins .

Is this system abuse? A little, but he does not fall into any multiple inheritance problems, because there is no state.

Of course, this is also the biggest drawback of this approach.

Answer 6

In the sense that Ruby mix-in is equivalent to the abstract Java class, no, you cannot implement mixing in Java. You can get closer with the help of interfaces and thus not specify absolutely any code in your mixing, but you cannot directly achieve the same behavior as in Ruby mix-in.

Answer 7

Take a look at http://code.google.com/p/javadude/wiki/AnnotationsMixinExample

It uses the set of annotations I created.

Note. I am working on a major annotation update that includes some broken APIs. I plan to release a new version in the next few weeks.

Answer 8

just ran: http://www.berniecode.com/blog/2009/08/16/mixins-for-java/

Answer 9

UPDATE: Qi4j is now an Apache training ground, https://polygene.apache.org

The Qi4j definition of Mixins is probably completely unique, as it does not start with a base class. Moving to this extreme, an entirely new paradigm for creating applications is emerging, and we call this composite-oriented programming. Composite is the equivalent of an “object”, not just Mixins connected together, but also constraints (validation), problems (around the board) and SideEffects (cannot change the result of the method).

So, I think Qi4j has a very strong Mixin story. Mixers can be "typed" or "generic", they can be public (available outside of the composite) or purely private (inside the Composite). Qi4j strongly determines what properties are and continues to have built-in persistence that does not leak the storage implementation into your domain (caveat; Qi4j leaks into your domain). And once persistent entities enter the picture, a strong definition of associations is also required (and included in Qi4j).

For a good overview, see http://www.qi4j.org/state-modeling.html .

In Qi4j, ONLY mixers have a state. Limitations / problems / SideEffects cannot have a state (if they need to summarize a personal mix).

To define a composite in Qi4j, you can either do it structurally on the types themselves, or at boot time when a runtime model is created.

Structurally;

 @Mixins({PetrolEngfineMixin.class, FourWheelsMixin.class}) public interface Car extends HasEngine, HasWheels, EntityComposite {} 

At boot time;

 public interface Car {} 

public class CarModuleAssembler implements Assembler {public void assemble (ModuleAssembly module) {module.entities (Car.class) .withMixins (PetronEngineMixin.class, FourWheelsMixin.class); }}

However, this simply concerns the surface of functions in Qi4j.

Answer 10

Faking mixins in Java: http://jonaquino.blogspot.com/2005/07/java-mixin-pattern-or-faking-multiple.html

Answer 11

Now you can make Mixins with Java (i.e. 5,6,7) using AspectJ ITDs . Java 8, of course, will add the best features with its security methods.

Answer 12

I believe this can answer your question ... although I'm not completely sure I understand what mixin is ...

Answer 13

Yes, the easiest and most convenient way to implement mixins apporoach in Java is to use static imports from some class that contains static methods.

Answer 14

I’m not sure which functions you use for mixins, but much of this can be done using the decorator template.

http://en.wikipedia.org/wiki/Decorator_pattern#Java

Answer 15

I am learning this for Java 7. My first cut will be to use the example shown in this article:

• Mixins in pure java

It should work with java 6, it is similar to other injection options above. Based on my experience with Mixins in C # and Ruby, you should strive to implement mixins, not just imitate or fake it.

Another model used with Jackson :

• Jackson MixIn annotations

If you can use the new version of Java 8, let's say if you are in pre-release mode, this may help.

• Java 8: do you have mixins now?

Using the Virtual Extension method, which requires effort for a 'be-a' mixin. Therefore, in my opinion, it is still early, and I prefer the approach with a cleaner look (or similar), proposed by the first link.

Answer 16

Is the term "mixin" not equivalent to the term "term" Java in aspect-oriented programming? AspectJ is probably worth a look.

Answer 17

The answer to the old question.

I took a look at Apache Zest. It may have been just me, but I find the examples a bit cumbersome. And I could not understand. Another alternative could be object commands.

But I suggest you take a look at this repo:

https://github.com/Mashashi/javaroles/

This may partially cover what you want to do. Seems simple.

Here is an example:

Defining an interface for roles:

 public interface Human { String hello(); String die(String age); String eat(); String dance(); } public interface Monkey {String hello(); String eat();} 

Defining a Hard Type AnimalRoles ...

 public class AnimalRoles implements Human, Monkey{ public static final String HALLO = "Default hallo"; public static final String DIE = "Default they kill me..."; public static final String EAT = "Default eat..."; @ObjectForRole public Human human; @ObjectForRole public Monkey monkey; public AnimalRoles(Human human, Monkey monkey){ this.human = human; this.monkey = monkey; if(this.human!=null){ ((Portuguese)this.human).core = this; } } @Override public String hello() { return HALLO; } @Override public String die(String age) { return DIE+age; } @Override @TurnOffRole public String eat() { return EAT; } @Override public String dance() { return "Just dance"; } public String notInRole(){ return "Oh oh"; } } 

Defining the role of the Bonobo class ...

 public class Bonobo implements Monkey{ public Bonobo() {} @Override public String hello(){ return "Ugauga"; } @Override public String eat() { return "Nhamnham"; } } 

Defining the role of the Portuguese class ...

 @RoleObject(types = { AnimalRoles.class }) public class Portuguese implements Human{ public static final String HALLO = "Hey there"; public static final String DIE = "They killed me"; public static final String EAT = "Eating boiled pork now"; public AnimalRoles core; public Portuguese() {} @Override public String hello() { return HALLO; } @Override public String die(String age) { return DIE+age; } @Override public String eat() { return EAT; } @Override public String dance() { return core.dance()+" modified!"; } } 

Running test ...

 new RoleRegisterComposition().registerRools(); AnimalRoles a = new AnimalRoles(new Portuguese(), new Bonobo()); System.out.println(a.hello()); System.out.println(a.dance()); 

There will be a seal ...

 "Hey there" "Dance modified!" 

Answer 18

Please see my small demo project on how to create mixes in pure java using cglib. Basically this is just a call to the proxy generator. This is an ally. The example contains a junit test case that demonstrates how to create a proxy server.

https://github.com/literadix/JavaMixins