CODEWITHSUNDEEP
javahashmapfactory
Code Newb
Code Newb

Reputation: 65

How to create constructor for Hashmap<String Boolean> in a factory method?

I am creating a factory method for a Hashmap in a public class.

 public class MyList {
    Hashmap list = newMap();   //is this function called properly here?

public static final Hashmap newMap() {
    return Hashmap(String, boolean);

  }
 }

In the simplest way, how do I set up the factory method if it is to hold a string and boolean for the key/value pair?

I'm stuck on the syntax.

I just want to return a new Hashmap object and use newMap() as a factory method

Upvotes: 1

Views: 1104

Answers (2)

NiksVij
NiksVij

Reputation: 193

To get a generic factory method with T and U as Class type you can go ahead with 

public static <T,U> HashMap<T,U> factoryHashMap(T t , U u ){
         HashMap<T,U> tuHashMap = new HashMap<T,U>();
         // do stuff
        return tuHashMap;
    }

Here T t, Uu are optional params . You can have empty params too .

If you observe before the return type HashMap<T,U> in function, we have put <T,U> to denote that this is a generic method

here T and U can be any valid class type . In your case it is String and Boolean

new HashMap<T,U> is the instance that is created and updated to your factory method's requirements .

for eg . In the below example we are simply adding t and u to the map, if they are not null else returning an empty HashMap

public static <T, U> HashMap<T, U> factoryHashMap(T t, U u) {
    HashMap<T, U> tuHashMap = new HashMap<T, U>();
    if (t != null && u != null)
        tuHashMap.put(t, u);
    return tuHashMap;
}

driver method :

public static void main(String args[] ) throws Exception {
        HashMap<String, Boolean> myMap = factoryHashMap("isItCool?",false);
}

Upvotes: 0

azro
azro

Reputation: 54168

  1. HashMap has generic types for key and value, so you need to specify these types as

    public static HashMap<String, Boolean> newMap() {
    // ...
}

  2. And inside, you'll create the map as

    • return new HashMap<String, Boolean>();
    • or just as return new HashMap<>(); using diamond operator (as type is already in the signature

  3. You could also pass the type as parameter

    public static <K, V> HashMap<K, V> newMap(Class<K> classKey, Class<V> classValue) {
    return new HashMap<>();
}

Use

public static void main(String[] args) {
    Map<String, Boolean> map = newMap();
    Map<Integer, Double> mapID = newMap(Integer.class, Double.class);
}

Upvotes: 1

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