如何在Java中将类型传递给泛型类？

Question

everyone here! I want pass a Type to a generic Type, like Arraylist, how can I do this? I make a simple Example, so that you will know what I want, of course this code is wrong.

public static void passObjType(Object obj) {

    Class clazz = obj.getClass();

    ArrayList<clazz> arr = new ArrayList<clazz>();

}

public static void main(String[] args) {

    HashSet<String> hs = new HashSet<String>();

    passObjType(hs);
}

I hope, if I input a HashSet object, the funktion PassObjType() will create a Arraylist with HashSet and If I input a String Object, then it will create a Arraylist with String. How can I do this?

Answer 1

You can try something like

public static <T> void passObjType(T obj) {
    ArrayList<T> arr = new ArrayList<T>();
    //...
}

public static void main(String[] args) {
    HashSet<String> hs = new HashSet<String>();
    passObjType(hs);
}

But I am not sure if that is what you want since at runtime generic types are erased and ArrayList<String> is just ArrayList (which can store any Object).

Answer 2

You can use Java Generics to get the parameter of Object type, as below :

        public static<T> void passObjType(T e) {
             ArrayList<T> arr = new ArrayList<T>();
        }

        public static void main(String[] args) {
            HashSet<String> hs = new HashSet<String>();
            String hp = new String();
            passObjType(hs);
            passObjType(hp);
        }