HashMaps and Null values?

Question

How do you pass in null values into a HashMap?
The following code snippet works with options filled in:

HashMap<String, String> options = new HashMap<String, String>();  
options.put("name", "value");
Person person = sample.searchPerson(options);  
System.out.println(Person.getResult().get(o).get(Id));    

So the issue is what has to be entered into the options and or method to pass in a null value?
I tried the following code without any success:

options.put(null, null);  
Person person = sample.searchPerson(null);    

options.put(" ", " ");  
Person person = sample.searchPerson(null);    

options.put("name", " ");  
Person person = sample.searchPerson(null);  

options.put();  
Person person = sample.searchPerson();    

Answer 1

HashMap supports both null keys and values

http://docs.oracle.com/javase/6/docs/api/java/util/HashMap.html

... and permits null values and the null key

So your problem is probably not the map itself.

Answer 2

You can keep note of below possibilities:

1. Values entered in a map can be null.

However with multiple null keys and values it will only take a null key value pair once.

Map<String, String> codes = new HashMap<String, String>();

codes.put(null, null);
codes.put(null,null);
codes.put("C1", "Acathan");

for(String key:codes.keySet()){
    System.out.println(key);
    System.out.println(codes.get(key));
}

output will be :

null //key  of the 1st entry
null //value of 1st entry
C1
Acathan

2. your code will execute null only once

options.put(null, null);  
Person person = sample.searchPerson(null);   

It depends on the implementation of your searchPerson method if you want multiple values to be null, you can implement accordingly

Map<String, String> codes = new HashMap<String, String>();

    codes.put(null, null);
    codes.put("X1",null);
    codes.put("C1", "Acathan");
    codes.put("S1",null);


    for(String key:codes.keySet()){
        System.out.println(key);
        System.out.println(codes.get(key));
    }

output:

null
null

X1
null
S1
null
C1
Acathan

Answer 3

It seems that you are trying to call a method with a Map parameter. So, to call with an empty person name the right approach should be

HashMap<String, String> options = new HashMap<String, String>();
options.put("name", null);  
Person person = sample.searchPerson(options);

Or you can do it like this

HashMap<String, String> options = new HashMap<String, String>();
Person person = sample.searchPerson(options);

Using

Person person = sample.searchPerson(null);

Could get you a null pointer exception. It all depends on the implementation of searchPerson() method.