Generics in Java

Question

Is there any shorthand way of defining and using generic definitions without having to keep repeating a particular generic description such that if there is a change I don't have to change all definitions/usages though out the codebase for example is something like this possible:

Typedef myGenDef = < Object1, Object2 >;

HashMap< myGenDef > hm = new HashMap< myGenDef >();

for (Entry< myGenDef > ent : hm..entrySet())
{
.
.
.
}

Answer 1

There's the pseudo-typedef antipattern...

class StringList extends ArrayList<String> { }

Good stuff, drink up! ;-)

As the article notes, this technique has some serious issues, primarily that this "typedef" is actually a separate class and thus cannot be used interchangeably with either the type it extends or other similarly defined types.

Answer 2

In a generic method, you can use a limited form of type inferrence to avoid some repetitions.

Example: if you have the function

    <K, V> Map<K, V> getSomething() {
        //...
    }

you can use:

final Map<String, Object> something = getsomething();

instead of:

final Map<String, Object> something = this.<String, Object>getsomething();

Answer 3

Use Factory Pattern for creation of Generics:

Method Sample:

public Map<String, Integer> createGenMap(){
        return new HashMap<String,Integer>();

    }

Answer 4

The pseudo-typedef antipattern mentioned by Shog9 would work - though it's not recommended to use an ANTIPATTERN - but it does not address your intentions. The goal of pseudo-typedef is to reduce clutter in declaration and improve readability.

What you want is to be able to replace a group of generics declarations by one single trade. I think you have to stop and think: "in witch ways is it valuable?". I mean, I can't think of a scenario where you would need this. Imagine class A:

class A {
     private Map<String, Integer> values = new HashMap<String, Integer>();
}

Imagine now that I want to change the 'values' field to a Map. Why would exist many other fields scattered through the code that needs the same change? As for the operations that uses 'values' a simple refactoring would be enough.

Answer 5

No. Though, groovy, a JVM language, is dynamically typed and would let you write:

def map = new HashMap<complicated generic expression>();