Question in Generic Methods

[Pranav Pal]

I have following code:

package core;

import java.util.HashMap;
import java.util.Map;

public class Test2 {

	public static void main(String[] args) {
		new Test2().doTest();
	}
	
	public void process(Map<String, HashMap<Long, ? extends Fruit>> buildingblocksmap){
		//do something here
	}
	
	
	public void doTest(){
		Map<String, HashMap<Long, Fruit>> buildingblocksmap = new HashMap<String, HashMap<Long, Fruit>>();
		process(buildingblocksmap);
	}
}

class Fruit{}

Compiling the above code gives following error:
Test2.java:19: process(java.util.Map<java.lang.String,java.util.HashMap<java.lang.Long,? extends core.Fruit>>) in core.Test2 cannot be applied to (java.util.Map<java.lang.String,java.util.HashMap<java.lang.Long,core.Fruit>>)
process(buildingblocksmap);
^
1 error
Can anybody please explain the reason of this error?

[Sai Hegde]

The process method signature needs to be changed to this.

public void process(Map<String, HashMap<Long, Fruit>> buildingblocksmap){  
        //do something here  
}

[Matt Cartwright]

Sai Hegde wrote:The process method signature needs to be changed to this.

public void process(Map<String, HashMap<Long, Fruit>> buildingblocksmap){  
        //do something here  
}

got it wrong first, but yes that works....

import java.util.HashMap;
import java.util.Map;


public class Test2
{

   public static void main( String[] args )
   {
      new Test2().doTest();
   }

   public void process( Map<String, HashMap<Long, Fruit>> buildingblocksmap )
   {
      // do something here
   }

   public void doTest()
   {

      HashMap<Long, Fruit> bramley = new HashMap<Long, Fruit>();
      HashMap<Long, Fruit> gala = new HashMap<Long, Fruit>();
      Map<String, HashMap<Long, Fruit>> store1 = new HashMap<String, HashMap<Long, Fruit>>();

      bramley.put(112L, new Apple());
      gala.put(121L, new Apple());

      store1.put("Bramley", bramley);
      store1.put("Gala", gala);

      process(store1);
   }

}

class Fruit{}
class Apple extends Fruit{}

[Sai Hegde]

I think you are confusing the compiler here...

Try this -

public static void main(String[] args) {
		HashMap<Long, Mango> mangoMap = new HashMap<Long, Mango>();
		Map<String, Map<Long, ? extends Fruit>> processMap = new HashMap<String, Map<Long, ? extends Fruit>>();
		processMap.put("mango", mangoMap);
		process(processMap);
	}
	
	public static void process(Map<String, Map<Long, ? extends Fruit>> fruitMap){
	           // Do something
                   //fruitMap.containsKey("mango");
	}

[Matt Cartwright]

Sai, you're right, the original method definition works alright