ArrayList<String> arreglo=new ArrayList();

ArrayList<Integer> arreglo=new ArrayList();

public class Box<T> {
    private T t;

    public void set(T t) { this.t = t; }
    public T get() { return t; }
}

Box<String> boxString = new Box();
boxString.set("abc");

Box<Integer> boxInteger = new Box();
boxInteger.set(100);

ArrayList<Object> arreglo=new ArrayList<>();