CODEWITHSUNDEEP
javatypeshashmapalias
Lee
Lee

Reputation: 3329

How do I create some variable type alias in Java?

Let's say I have this code

Map<String, String> list = new HashMap<String, String>();
list.put("number1", "one");
list.put("number2", "two");

how can I make some "alias" the type

Map<String, String>

to something that easier to be rewritten like

// may be something like this
theNewType = HashMap<String, String>;

theNewType list = new theNewType();
list.put("number1", "one");
list.put("number2", "two");

Basically, my question is, how to create "alias" to some "type", so I can make it easier to write and easier when need to change the whole program code.

Thanks, and sorry if this is silly question. I'm kinda new in Java.

Upvotes: 97

Views: 77759

Answers (5)

Rom1
Rom1

Reputation: 3207

There is no typedef equivalent in Java, and there is no common idiom for aliasing types. I suppose you could do something like

class StringMap extends HashMap<String, String> {}

but this is not common and would not be obvious to a program maintainer.

Upvotes: 18

Andrey
Andrey

Reputation: 839

Although Java doesn't support this, you can use a generics trick to simulate it.

class Test<I extends Integer> {
    <L extends Long> void x(I i, L l) {
        System.out.println(
            i.intValue() + ", " + 
            l.longValue()
        );
    }
}

Source: http://blog.jooq.org/2014/11/03/10-things-you-didnt-know-about-java/

Upvotes: 13

Ingo
Ingo

Reputation: 36349

The closest one could think of is to make a wrapper class like so

class NewType extends HashMap<String, String> {
     public NewType() { }
}

I really wish Java had a sound type aliasing feature.

Upvotes: 4

KARASZI Istv&#225;n
KARASZI Istv&#225;n

Reputation: 31467

There are no aliases in Java. You can extend the HashMap class with your class like this:

public class TheNewType extends HashMap<String, String> {
    // default constructor
    public TheNewType() {
        super();
    }
    // you need to implement the other constructors if you need
}

But keep in mind that this will be a class it won't be the same as you type HashMap<String, String>

Upvotes: 85

Michael Borgwardt
Michael Borgwardt

Reputation: 346377

Nothing like that exists in Java. You might be able to do something with IDE templates or autocompletion, and look forward to (limited) generics type inference in Java 7.

Upvotes: 1

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