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  1.  
  2. import java.util.*;
  3. import java.lang.reflect.*;
  4.  
  5. class Example {
  6.     public static void main(String[] args) {
  7.         try {
  8.         	// OK
  9.         	System.out.println(getClassE( new ArrayList<String>() {} ));
  10.  
  11.         	// also OK
  12.         	class StringList extends ArrayList<String> {}
  13.         	System.out.println(getClassE( new StringList() ));
  14.  
  15.         	// not OK
  16.         	System.out.println(getClassE( new ArrayList<String>() ));
  17.  
  18.         } catch(Throwable e) {
  19.             e.printStackTrace(System.out);
  20.         }
  21.     }
  22.  
  23.     static <E> Class<E> getClassE(List<E> list) {
  24. 	    Class<?> listClass = list.getClass();
  25.  
  26. 	    Type gSuper = listClass.getGenericSuperclass();
  27. 	    if(!(gSuper instanceof ParameterizedType))
  28. 	        throw new IllegalArgumentException();
  29.  
  30. 	    ParameterizedType pType = (ParameterizedType)gSuper;
  31.  
  32. 	    Type tArg = pType.getActualTypeArguments()[0];
  33. 	    if(!(tArg instanceof Class<?>))
  34. 	        throw new IllegalArgumentException();
  35.  
  36. 	    @SuppressWarnings("unchecked")
  37. 	    final Class<E> classE = (Class<E>)tArg;
  38. 	    return classE;
  39. 	}
  40. }
Success #stdin #stdout 0.11s 320256KB
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Standard input is empty
stdout
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class java.lang.String
class java.lang.String
java.lang.IllegalArgumentException
	at Example.getClassE(Main.java:34)
	at Example.main(Main.java:16)
https://ideone.com/O2Gztj
language:
Java (HotSpot 12)
created:
9 years ago
visibility:
secret

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