java - Create enum with entries associated to classes -

supposing have several specific classes extend 1 abstract class, so:

public abstract abstractclass {   // abstract stuff here }  public firstspecificclass extends abstractclass {   // specific stuff here }  public secondspecificclass extends abstractclass {   // specific stuff here } 

i need create enum elsewhere in each entry connected (associated?) 1 of specific classes; end, passing specific class constructor parameter , storing private field within enum (i've provided getter method field). need create static method takes instance of 1 of specific classes argument , returns appropriate enum element (or null). looping on each enum entry , using instanceof in combination getter private field mentioned previously. attempt:

public enum types {   first(firstspecificclass.class),   // line 2   second(secondspecificclass.class); // line 3    private class<abstractclass> classtype;    private types(class<abstractclass> classtype) {     this.classtype = classtype;   }    public class<abstractclass> getclasstype() {     return this.classtype;   }    public static types fromtypeinstance(abstractclass instance) {     for(types t : types.values())       if(instance instanceof t.getclasstype()) return t; // line 17     return null;   } } 

i seem misunderstanding how store class type field can returned , used in instanceof check later. code producing several compile-time errors:

• (line 2 of enum): constructor types(class<firstspecificclass>) undefined
• (line 3 of enum): constructor types(class<secondspecificclass>) undefined
• (line 17 of enum): incompatible operand types boolean , class<abstractclass>

i not java programmer, , understanding of generics , instanceof fuzzy @ best, although have pretty firm grasp on concept of oop. how can resolve these errors , achieve desired effect?

in java, generics invariant. means class<firstspecificclass> not class<abstractclass>, if firstspecificclass abstractclass.

you can work around explicitly allowing subtypes upper bound wildcard. add ? extends before abstractclass type argument needed.

private class<? extends abstractclass> classtype;  private types(class<? extends abstractclass> classtype) {    this.classtype = classtype; }  public class<? extends abstractclass> getclasstype() {    return this.classtype; } 

additionally, must specify type directly in source code instanceof operator, doesn't compile:

if(instance instanceof t.getclasstype()) 

you can use class object's isinstance method instead, runtime solution:

if(t.getclasstype().isinstance(instance))