map method containsKey

[Neeraj Vij]

Hi,

I have a small issue, which I am unable to get -- kinldy provide guidance

    
map.containsKey(object)  returns true

while

  
map.get(object) returns null 
 

object is JavaBean in our code


thanks
Neeraj

[Henry Wong]

You have a map, with a key, whose pair has a value of null?

Henry

[Sebastian Janisch]

Henry Wong wrote:
You have a map, with a key, whose pair has a value of null?

Henry

Yep, this..

map.put(object, null)

is perfectly legal to do ..

[Muhammad Khojaye]

As per Javadocs

V get(Object key)
Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

What part you unable to get?

[Jesper de Jong]

Muhammad: The issue is that the map not only returns null if the key is not in the map, it can also return true if the key is in the map - with the value null.

[Neeraj Vij]

thanks a ton for your inputs.

i got it that.it can also return true if the key is in the map - with the value null.

but in our case the value of the object is not null. when I try to iterate through the map using map.values. it returns a non-null collection.

thanks
Neeraj

[Henry Wong]

Neeraj Vij wrote:
but in our case the value of the object is not null. when I try to iterate through the map using map.values. it returns a non-null collection.

The values() method always return a non-null collection. Or are you saying that it returns a collection that doesn't have a null in it?

Henry

[Neeraj Vij]

yes. it returns a collection that doesn't have a null in it. its an arraylist of size 1. with proper values in that arraylist.

just for my help. can you please clarify. will map.values return a non null collection even if the map size is zero.

thanks
Neeraj.

[Mike Simmons]

Neeraj Vij wrote:just for my help. can you please clarify. will map.values return a non null collection even if the map size is zero.

Yes - in this case, it will return a collection of size zero.

Neeraj Vij wrote:i got it that.it can also return true if the key is in the map - with the value null.

This may be a problem with the key. What class is it? Have you defined your own equals() and hashCode() methods for this class? If so, I suggest you show them here. A problem with these can prevent a HashMap from working correctly.

[Rob Spoor]

But shouldn't that break containsKey as well?

[Mike Simmons]

True - I didn't read that part.

[Neeraj Vij]

yes. we have defined equals and hashcode method for the bean class that are put into the hashmap. I was also surprise it was not breaking the conatinskey.

here is the actual code for equals method..it's not a nice one.

  
public boolean equals(Object obj){
		if (obj instanceof DescriptionBean){
			DescriptionBean projectDescription = (DescriptionBean) obj;
			if (this.projectCode != null){
				System.out.println(" projectdescription comparison for project code ");
				return this.projectCode.equals(projectDescription.projectCode);
			}else{
				System.out.println(" projectdescription comparison for request code " +this.requestCode.equals(projectDescription.requestCode));
				return this.requestCode.equals(projectDescription.requestCode);
			}
		}else
			return false;
	}

 

thanks for your inputs
neeraj

[Campbell Ritchie]

Moving thread as too difficult for "beginning."

[Mike Simmons]

So, is there a hashCode() method to go with the equals()?

[Neeraj Vij]

yes.

it's also not nice one

   

public int hashCode(){
		System.out.println("INSIDE HASHCODE project code---- > " +this.projectCode);
		System.out.println("INSIDE HASHCODE requestCode code---- > " +this.requestCode);
		if (this.projectCode != null){
			return this.projectCode.hashCode();
		}else{
			return this.requestCode.hashCode();
		}
	}
 

thanks
neeraj