Blocks.java

class Block implements MetaOwner<Block> {

}

Components.java

interface Meta<T> {
    void init(Meta<T> meta);
    void apply(MetaOwner<T> owner);
    void update();
    void remove(MetaOwner<T> owner);
}

interface MetaOwner<U> {
    <M extends Meta<U>> M obtainMeta(Class<M> cls);
    <M extends Meta<U>> M applyMeta(Class<M>... cls);
}

interface DefaultMeta<T> extends Meta<T> {
    default void init(Meta<T> meta){
    }

    default void apply(MetaOwner<T> owner) {
    }

    default void update() {
    }

    default void remove(MetaOwner<T> owner) {
    }
}

interface EntityMeta extends DefaultMeta<Entity> {
    EntityType[] ownedBy();
}

interface BlockMeta extends DefaultMeta<Block> {
    Substance[] ownedBy();
}

interface ItemMeta extends DefaultMeta<Item> {
    Substance[] ownedBy();
}

Entities.java

class Entity implements MetaOwner<Entity> {
    
}

Implementations.java

class AgeImpl implements Age {
    private volatile int age;
    @Override public boolean isBaby() {
        return age < 68;
    }
    
    @Override public int get() {
        return age;
    }
    
    @Override public void set(int age) {
        this.age = age;
    }
}

class DisplayNameImpl implements DisplayName {
    private volatile String name;
    @Override public boolean hasName() {
        return name != null;
    }
    
    @Override public String get() {
        return this.name;
    }
    
    @Override public void set(String name) {
        this.name = name;
    }
}

Interfaces.java

interface Age extends EntityMeta {
    boolean isBaby();
    int get();
    void set(int age);
}

interface DisplayName extends EntityMeta, ItemMeta {
    boolean hasName();
    String get();
    void set(String name);
}

Items.java

class Item implements MetaOwner<Item> {
    
}

Usage.java

// Entities
Entity entity = world.spawn(EntityType.ZOMBIE, position);
Age a = entity.obtainMeta(Age.class);
DisplayName name = entity.obtainMeta(DisplayName.class);
if (a.isBaby()) {
   a.set(69);
   name.set("Adult");
}

entity.applyMeta(a, name);

// Items
Item item = new Item(Substance.STICK);
DisplayName name = item.obtainMeta(DisplayName.class);
name.set("ayy lmao");
item.applyMeta(name);