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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.lang.reflect.Field;
  4. import java.lang.reflect.Modifier;
  5. import java.util.TreeSet;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Ideone {
  9. 	public static void main (String[] args) throws java.lang.Exception {
  10.         System.out.println( "Keys1: " + new Keys1().keySet() );
  11.         System.out.println( "Keys2: " + new Keys2().keySet() );
  12. 	}
  13. }
  14.  
  15. class Keys1 {
  16.     public static final ClassValue<TreeSet<String>> KEYS = new ClassValue<TreeSet<String>>() {
  17.         @Override protected TreeSet<String> computeValue(Class<?> type) {
  18.             final int desired=Modifier.PUBLIC|Modifier.STATIC|Modifier.FINAL;
  19.             Field[] fields=type.getDeclaredFields();
  20.             TreeSet<String> set = new TreeSet<>();
  21.             for(Field f: fields) {
  22.                 if((f.getModifiers()&desired)==desired && f.getType()==String.class) try {
  23.                     set.add((String)f.get(null));
  24.                 } catch(IllegalAccessException ex) {
  25.                     throw new AssertionError(ex);
  26.                 }
  27.             }
  28.             for(Class<?> inner: type.getDeclaredClasses()) {
  29.                 set.addAll(get(inner));
  30.             }
  31.             type = type.getSuperclass();
  32.             if(type != null && type != Object.class) set.addAll(get(type));
  33.             return set;
  34.         }
  35.     };
  36.     public TreeSet<String> keySet() {
  37.         return KEYS.get(getClass());
  38.     }
  39.  
  40.     public static final String AFIELD = "example";
  41. }
  42.  
  43. // no additional steps required, the inherited keySet() does the job
  44. class Keys2 extends Keys1 {
  45.     public static final String ANOTHER_FIELD = "subclass example";
  46.  
  47.     static class Inner {
  48.         public static final String FIELD = "innerclass example";
  49.     }
  50. }
Success #stdin #stdout 0.05s 4386816KB
comments (?)
stdin 
Standard input is empty
stdout 
Keys1: [example]
Keys2: [example, innerclass example, subclass example]
https://ideone.com/iGY0o9
language:
Java (HotSpot 12)
created:
7 years ago
visibility:
public

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