如何使用通用类型调用LinkedList

Question

I'm using several LinkedList each one from different type, for example :

 LinkedList<A> typeA = new LinkedList<>();
 LinkedList<B> typeB = new LinkedList<>();
 LinkedList<C> typeC = new LinkedList<>();

and then i want to print them according to the type, so for each type I call to the appropriate function.

void funcA(LinkedList<A> ls)
void funcB(LinkedList<B> ls)
void funcC(LinkedList<C> ls)

and I wonder if the is any option of calling one function and inside that function to check the type. Thank for those who help! Have a nice day :)

Answer 1

As other have mentioned, you can use a generic function like:

public static <T> void genericFunc(LinkedList<T> ls) { 
//you can do something with the list but 
//you do not know what T is so you can't invoke T's methods 
//(apart from those belonging to Object)
}

If you want to have additional control over the types contained in T, assuming that all your objects inherit from a base class A, then you can do:

public static <T extends A> void genericFunc(LinkedList<T> ls) { 
   for (T t : ls){
       t.somePublicMethodOfA(); 
   }
}

Answer 2

I'd use another generic parameter to the function to indicate how the list is to be printed based on the type.

See http://www.functionaljava.org/javadoc/4.7/functionaljava/fj/Show.html

Example:

void func<A>(LinkedList<A> list, Show<A> aShow) {
  listShow(aShow).printLn(list)
}

If you were using Scala you would make Show[A] an implicit parameter.

Answer 3

you can use a generic method.

public <T> void func(LinkedList<T> ls) { // T can be any type
   // do something
}

Answer 4

You could use a unbound generic type in the list parameter of the method, it would look as follow:

public static void main(String[] args) {
    List<String>  listStr = Arrays.asList("A","B","C");
    List<Integer> listInt = Arrays.asList(1,2,3);
    printList(listStr);
    printList(listInt);

}

private static void printList(List<?> list) {
    for(Object obj : list){
        if(obj instanceof String){
            String str = (String) obj;
            System.out.printf("String: %s \n", str);
        } else if(obj instanceof Integer){
            Integer integer = (Integer) obj;
            System.out.printf("Integer: %s \n", integer);
        }

    }

}