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/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static <K, V, T extends Collection<V>> boolean addToGroupMap(K key, V value, Map<K, T> checkMap){
	    assert checkMap!=null;
	    boolean result = false;
 
	    Collection<V> vList = checkMap.get(key);
	    if (vList==null){
	        checkMap.put(key, new T(Collections.singleton(value)));
	    }else {
	        vList.add(value);
	        result = true;
	    }
	    return result;
	}
 
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
	}
}

Main.java:16: error: unexpected type
	        checkMap.put(key, new T(Collections.singleton(value)));
	                              ^
  required: class
  found:    type parameter T
  where T,K,V are type-variables:
    T extends Collection<V> declared in method <K,V,T>addToGroupMap(K,V,Map<K,T>)
    K extends Object declared in method <K,V,T>addToGroupMap(K,V,Map<K,T>)
    V extends Object declared in method <K,V,T>addToGroupMap(K,V,Map<K,T>)
1 error

Standard output is empty