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POusing enum constants obtained through reflection
 

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  1. POusing enum constants obtained through reflection
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    <p>I have a program which obtains an Enum value via reflection (any Enum is allowed), and I want to do something with it by wrapping it in a generic class that takes an Enum as its type parameter. I am not sure how to properly call the constructor, however. The only way I can get it to work is to use a raw type.</p> <p>(<strong>clarification:</strong> My real program is complicated, and looks up the enum classname from a user-provided file at runtime. My real program's wrapper class has additional state and methods that cannot be accomplished with an enum, so I'm not just doing this for academic sake. I wrote the example program below to illustrate the issue. It may look contrived, but it's supposed to be for illustrative purposes.)</p> <p>Can anyone help me fix the line</p> <pre><code>EnumWrapper&lt;?&gt; ewrapped = new EnumWrapper(e); </code></pre> <p>below so it has a less evil warning? </p> <p>The program works as expected (prints out stack traces of 3 caught exceptions for enum constants not found, otherwise prints lists of wrapped enums), but I make it a habit never to use raw types, and don't know how to fix this case.</p> <pre><code>import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class GenericEnum2 { enum Bird { OWL, EAGLE, HAWK }; enum Mammal { LION, TIGER, BEAR }; static class EnumWrapper&lt;E extends Enum&lt;E&gt;&gt; { final private E value; public EnumWrapper(E value) { this.value = value; } public E getEnum() { return this.value; } @Override public String toString() { return "wrapped "+value.toString(); } static public &lt;E extends Enum&lt;E&gt;&gt; EnumWrapper&lt;E&gt; wrap(E e) { return new EnumWrapper&lt;E&gt;(e); } } public static void main(String[] args) { List&lt;EnumWrapper&lt;?&gt;&gt; list = new ArrayList&lt;EnumWrapper&lt;?&gt;&gt;(); list.add(EnumWrapper.wrap(Bird.OWL)); list.add(EnumWrapper.wrap(Bird.EAGLE)); list.add(EnumWrapper.wrap(Bird.HAWK)); list.add(EnumWrapper.wrap(Mammal.LION)); list.add(EnumWrapper.wrap(Mammal.TIGER)); list.add(EnumWrapper.wrap(Mammal.BEAR)); System.out.println(list); list.clear(); for (String s : Arrays.asList( "Bird.OWL", "Bird.HAWK", "Bird.FULVOUS_WHISTLING_DUCK", "Mammal.LION", "Mammal.BEAR", "Mammal.WARTHOG", "Computer.COMMODORE_64" )) { String className = GenericEnum2.class.getCanonicalName()+"$"+s; try { Enum&lt;?&gt; e = getEnum(className); // EnumWrapper&lt;?&gt; ewrapped0 = EnumWrapper.wrap(e); /* * Bound mismatch: The generic method wrap(E) of type * GenericEnum2.EnumWrapper&lt;E&gt; is not applicable for * the arguments (Enum&lt;capture#2-of ?&gt;). The inferred * type Enum&lt;capture#2-of ?&gt; is not a valid substitute for * the bounded parameter &lt;E extends Enum&lt;E&gt;&gt; */ // EnumWrapper&lt;?&gt; ewrapped0 = new EnumWrapper&lt;?&gt;(e); // Cannot instantiate the type GenericEnum2.EnumWrapper&lt;?&gt; EnumWrapper&lt;?&gt; ewrapped = new EnumWrapper(e); // this works but gives me the warning of "EnumWrapper" being a raw type list.add(ewrapped); } catch (IllegalArgumentException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } System.out.println(list); } static public Enum&lt;?&gt; getEnum(String enumFullName) throws IllegalArgumentException, ClassNotFoundException { String[] x = enumFullName.split("\\.(?=[^\\.]+$)"); if (x.length == 2) { String enumClassName = x[0]; String enumName = x[1]; @SuppressWarnings("unchecked") final Class&lt;Enum&gt; cl = (Class&lt;Enum&gt;)Class.forName(enumClassName); if (cl.isEnum()) { @SuppressWarnings("unchecked") final Enum result = Enum.valueOf(cl, enumName); return result; } else throw new IllegalArgumentException("Class is not an enum: "+enumClassName); } return null; } } </code></pre> <hr> <p>edit: updated getEnum() per OrangeDog's suggestions:</p> <pre><code>static public Enum&lt;?&gt; getEnum(String enumFullName) throws IllegalArgumentException, ClassNotFoundException { String[] x = enumFullName.split("\\.(?=[^\\.]+$)"); if (x.length == 2) { String enumClassName = x[0]; String enumName = x[1]; final Class&lt;?&gt; cl = Class.forName(enumClassName); if (cl.isEnum()) { for (Object o : cl.getEnumConstants()) { Enum&lt;?&gt; e = (Enum&lt;?&gt;)o; if (enumName.equals(e.name())) return e; } } else throw new IllegalArgumentException("Class is not an enum: "+enumClassName); } return null; } } </code></pre>
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    1. USJason S
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    1. COThis example is rather complicated. I would suggest making the code much simpler and dropping the wrapper.
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      1. USPeter Lawrey
    2. COAgreed, I don't see any useful method there except for the static factory method.
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      1. USmaaartinus
    3. COThis appears to be a complicated way to write `Arrays.asList(Bird.OWL, Bird.EAGLE, Bird.HAWK, Mammal.LION, Mammal.TIGER, Mammal.BEAR)`
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      1. POusing enum constants obtained through reflection
      1. USPeter Lawrey
 

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