如何从适用于多种 Class 类型的方法返回实际类型而不是 Object 类型？

Question

Is there any way to modify the findModel method in SubService to return a Foo or Boo type rather than an Object type .

I'd like to be able to just call findModel from FooService or BooService without casting to a Foo or Boo model object.

Is that possible?

SubService:

public Object findModel(long id, Class modelClass) {

    Object modelObject = null;
    javax.jdo.Query query = persistenceManager.newQuery(modelClass);
    query.setFilter("id == idParam");
    query.declareParameters("long idParam");
    List<Object> modelObjects = (List<Object>) query.execute(id);
    if(modelObjects.isEmpty()){
        modelObject = null;
    }
    else{
        modelObject = modelObjects.get(0);
    }
    return modelObject;

}

FooService extends SubService:

public Foo getFoo(long id) {

    Foo modelObject = (Foo)this.findModel(id, Foo.class);
    return modelObject;

}

BooService extends SubService:

public Boo getBoo(long id) {

    Boo modelObject = (Boo)this.findModel(id, Boo.class);
    return modelObject;

}

Answer 1

Redefine method with generics:

public <T> T findModel(long id, Class<T> modelClass)

Now it will return what you need and you do not need casting.

Answer 2

Cast your objects in you findModel to SubService

public SubService findModel(long id, Class modelClass)  {
     return (SubService) modelObject;
}

Then you can drop the casting in fooService

Foo modelObject = this.findModel(id, Foo.class);