Generic for HashMap holding different values

[Praful Thakare]

Hi,
May be too basic question, but haven't worked much on generics,following is my scenario.

I have parentHash map that will hold one more child hashmap for every key, and this childhashmap can hold

1) HashMap <String,HashMap> or
2) HashMap<String,String>.

so how do i define parent hashmap using generics?

-P

[Wouter Oet]

It is not possible for a generic HashMap to hold HashMaps and Strings (unless you're using a Object reference but that will nullify the advantages of generics). A solution would be do separate the 2 Maps in 2 classes and use a common interface to access them.

[Campbell Ritchie]

Praful Thakare wrote: . . . HashMap <String,HashMap> . . .

Map<String, Map>, surely?

[Praful Thakare]

thanks much Wouter, thats cool solution.

[Praful Thakare]

yes Campbell its HashMap<String, HashMap>

-P

[John de Michele]

Praful,

Campbell was trying to hint that it should be Map<String, Map>.

John.

[Praful Thakare]

thanks John...had doubt abt it but was't sure , but now not able to understand the difference between HashMap<String, HashMap> and Map<Stgring,Map> can you explain ?

[John de Michele]

Praful:

It's the idea of programming against interfaces, rather than implementations. For example, if I do this:

HashMap<String, String> map = new HashMap<String, String>()

I'm locking myself into an implementation - which may at some later point be difficult to change, or may be impossible to change if I expose methods in a public API.

If I do this:

Map<String, String> map = new HashMap<String, String>()

I can be assured that if I need to make a change at a later date (say, like it turns out that a TreeMap would work better), then all I have to do is change that one line of code, and I don't have to worry about my class' public API.

John.

[Jinglong Wang]

maybe you can

Map<String,Map<String,String>> hashMap = new HashMap<String,Map<String,String>>()