CODEWITHSUNDEEP
javagenerics
user3269829
user3269829

Reputation: 141

Instantiating a class which has generic params?

I have below class created.

public class SomeRequest<B extends Billing,E extends Employee, L extends Level>{


B billing;


E employee;

Class<L> level;

public void process(HashMap<String, Object> input){

        this.billing = (B)data.get("billing");
    this.employee= (E)data.get("employee");
    this.level = (Class<L>)data.get("level");

         //Some logic

  }

}

In above class Employee, Billing and Level are Java POJOs.

Now how can i instantiate above SomeRequest class?

Thanks!

Upvotes: 0

Views: 67

Answers (3)

A. A. Vybegallo
A. A. Vybegallo

Reputation: 246

In Java 5 or 6 you can use factory method as replacement for constructor with generics. In Java 5 or 6 type inference work fine on methods but not on constructors. You can write something like:

public class SomeRequest<B extends Billing,E extends Employee, L extends Level>{
   private SomeRequest(B billing, E employee, L level) {
       // ...
   }

   public static <B,E,L> with(B billing, E employee, L level) {
        return new SomeRequest<B, E, L>(billing, employee, level);
   }
}

Now you should't write new SomeRequest(billing, employee, level), you can write simple SomeRequest.with(billing, employee, level).

Oh, sorry, I asked before have seen your comment about Java 7.

Upvotes: 0

A. A. Vybegallo
A. A. Vybegallo

Reputation: 246

@user3269829 you should not use HashMap for contain data of different types. You can add custom container, i.e. a class with three field:

class Container<B extends Billing,E extends Employee, L extends Level> {

    B billing;

    E employee;

    L level;

    public Container(B b, E e, L l) {
        billing = b;
        employee = e;
        level = l;
    }

    // ... getters only!
}

The process() method will have next signature:

 public void process(Container<B, E, L> input)

In the process() method you can:

SomeRequest<Billing,Employee,Level> instance = new SomeRequest<>();
instance.setBilling(container.getBilling());
instance.setEmployee(container.getEmployee());
instance.setLevel(container.getLevel());

or

SomeRequest<Billing,Employee,Level> instance = new SomeRequest<>(container.getBilling(), container.getEmployee(), container.getLevel());

Upvotes: 0

Narendra Pathai
Narendra Pathai

Reputation: 41935

Assuming that SomeRequest class has a no-arg constructor

In Java 7 using the diamond operator

SomeRequest<Billing,Employee,Level> instance = new SomeRequest<>();

In Java 6 or 5

SomeRequest<Billing,Employee,Level> instance = new SomeRequest<Billing,Employee,Level>();

Upvotes: 1

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