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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 void main (String[] args) throws java.lang.Exception
	{
		List<Specific> specificList = Arrays.asList(new Specific(), new Specific());
        Map<Integer, ? extends Abstract> abstractMap = new HashMap<>();
 
        specificList.forEach(device -> abstractMap.put(device.getIdentity(), device));
	}
}
 
class Abstract { 
	Integer identity; 
 
	Abstract() {
		Random rand = new Random(); 
		identity = rand.nextInt(9000);
	}
 
	public Integer getIdentity() {
		return identity;
	}
}
 
class Specific extends Abstract { }

Main.java:15: error: incompatible types: Specific cannot be converted to CAP#1
        specificList.forEach(device -> abstractMap.put(device.getIdentity(), device));
                                                                             ^
  where CAP#1 is a fresh type-variable:
    CAP#1 extends Abstract from capture of ? extends Abstract
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
1 error

Standard output is empty