Question

I am trying to make the following method to a generic method and got struck.

public static MyObject[] getObjectFromList(List<MyObject> inputList) {
        if (inputList != null && inputList.size() > 0) {
            return inputList.toArray(new MyObject[inputList.size()]);
        } else {
            inputList = new ArrayList<MyObject>();
            MyObject obj = new MyObject();
            inputList.add(obj);
            return inputList.toArray(new MyObject[inputList.size()]);
        }
    }

and have the other method which is similar but it’s MyObject2

public static MyObject2[] getObjectFromList(List<MyObject2> inputList) {
            if (inputList != null && inputList.size() > 0) {
                return inputList.toArray(new MyObject2[inputList.size()]);
            } else {
                inputList = new ArrayList<MyObject2>();
                MyObject2 obj = new MyObject2();
                inputList.add(obj);
                return inputList.toArray(new MyObject2[inputList.size()]);
            }
        }

How do I make this as a single method which takes any object(myobject,myobject2) list and
returns an array ?

Answer 1

You can’t do it without changing method signature due to type erasure. If you can pass a Class object identifying the desired type you can do something like this:

public static <T> T[] getObjectFromList(List<? extends T> inputList, Class<T> c) {
    if (inputList == null || inputList.isEmpty()) {
        inputList = new ArrayList<T>();
        T obj = null;
        try {
            obj = c.newInstance();
        } (Exception ex) {
            throw new RuntimeException("Instantiation failed", ex);
        }
        inputList.add(obj);
    }             
    return inputList.toArray(Array.newInstance(c, inputList.size()));            
}