JAVA 深入理解 古怪的循环泛型、自限定、参数协变

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古怪的循环泛型 自限定参数协变

package CuriouslyRecurringGeneric;

public class BasicHolder<T> {
    T element;

    public T get() {
        return element;
    }

    public void set(T element) {
        this.element = element;
    }

    void f(){
        System.out.println(element.getClass().getSimpleName());
    }
}

package CuriouslyRecurringGeneric;

class Base{}
class Derived extends Base{}

interface OrdinaryGetter{
    Base get();
}

interface DeriveGetter extends OrdinaryGetter{
    Derived get();
}

//谐变返回类型
public class CovariantRreturnTypes {
    void test(DeriveGetter d){
        Derived d2 = d.get();
    }

    public static void main(String [] argv){
        CovariantRreturnTypes crt = new CovariantRreturnTypes();
    }
}

package CuriouslyRecurringGeneric;

class Subtyppe extends BasicHolder<Subtyppe>{}


public class CRGWithBasicHolder {
    public static void main(String[] args){
        Subtyppe st1 = new Subtyppe(), st2 = new Subtyppe();
        st1.set(st2);
        Subtyppe st3 = st1.get();
        st1.f();
    }
}

package CuriouslyRecurringGeneric;

interface GenericGetter<T extends GenericGetter<T>>{
    T get();
}


interface Getter extends GenericGetter<Getter>{

}

public class GenericAndReturnTypes {
    void test(Getter g){
        Getter result = g.get();
        GenericGetter gg = g.get();
    }
}

package CuriouslyRecurringGeneric;


public class GenericType<T> {
    //古怪的循环泛型
    public class CuriouslyRecurringGeneric extends GenericType<CuriouslyRecurringGeneric>{

    }
}

package CuriouslyRecurringGeneric;

public class NotSelfBounded<T> {
    T element;

    NotSelfBounded<T> set(T arg){
        element = arg;
        return this;
    }

    T get(){return  element;}

    public static void main(String [] argv){
        NotSelfBounded<Integer> n = new NotSelfBounded<>();
        NotSelfBounded<Integer> s = n.set(10);
    }
}

class A2 extends NotSelfBounded<A2>{}
class B2 extends NotSelfBounded<A2>{}

class C2 extends NotSelfBounded<C2>{
    C2 setAndGet(C2 arg){
        set(arg);
        return get();
    }
}

class D2{}

class E2 extends NotSelfBounded<D2>{}

package CuriouslyRecurringGeneric;

class OrdinarySetter{
    void set(Base base){
        System.out.println("OrdinarySetter.set(Base base){");
    }
}

class DeriveSetter extends OrdinarySetter{
    void set(Derived derived){
        System.out.println("DeriveSetter.set(Derived derived){");
    }
}

public class OrdinaryArgments {
    public static void main(String [] argv){
        Base base = new Base();
        Derived derived = new Derived();
        DeriveSetter ds = new DeriveSetter();
        ds.set(base);
        ds.set(derived);
    }
}

package CuriouslyRecurringGeneric;

class GenericSetter<T>{
    void set(T arg){
        System.out.println("GenericSetter.set(Base)");
    }
}

class DerivedGS extends GenericSetter<Base>{
    void set(Derived derived){
        System.out.println("DerivedGS.set(Derived)");
    }
}

public class PlainGenericInheritance {
    public static void main(String [] argv){
        Base base = new Base();
        Derived derived = new Derived();
        DerivedGS dgs = new DerivedGS();
        dgs.set(base);
        dgs.set(derived);
    }
}

package CuriouslyRecurringGeneric;

class SelfBounded<T extends  SelfBounded<T>>{
    T element;

    SelfBounded<T> set(T arg){
        element= arg;
        return this;
    }

    T get(){
        return element;
    }
}

class A extends SelfBounded<A>{}
class B extends SelfBounded<A>{}

class C extends SelfBounded<C>{
    C setAndGet(C arg){
        set(arg);
        return  get();
    }
}


class D{};
//class E extends SelfBounded<D>{} //此处出错

class F extends SelfBounded{} //OK

//自限定的类
public class SelfBounding {
    public static void main(String [] argv){
        A a = new A();
        a.set(new A());

        a.set(new A()).get();
        a=a.get();

        C c = new C();
        c = c.setAndGet(new C());
    }
}

package CuriouslyRecurringGeneric;

interface SelfBoundSetter<T extends SelfBoundSetter<T>>{
    void set(T arg);
}

interface Setter extends SelfBoundSetter<Setter>{}

public class SelfBoundingAndCovariantArguments {
    void testA(Setter s1, Setter s2, SelfBoundSetter sbs){
        s1.set(s2);
        //s1.set(sbs); //error
    }
}

package CuriouslyRecurringGeneric;

public class SelfBoundingMethods {
    static <T extends SelfBounded<T>> T f(T arg){
        return arg.set(arg).get();
    }

    public  static void main(String[] args){
        A a = f(new A());
    }
}

package CuriouslyRecurringGeneric;


class Other{}
class BasicOther extends BasicHolder<Other>{}

//不受限定的类
public class Unconstrained {
    public static void main(String [] argv){
        BasicOther b = new BasicOther(), b2 = new BasicOther();
        b.set(new Other());
        Other other = b.get();
        b.f();
    }
}