Calling constructor of a generic type

Question

If I have an abstract class like this:

public abstract class Item
{
    private Integer value;
    public Item()
    {
        value=new Integer(0);
    }
           


        

Answer 1

There is no way to use the Java type system to enforce that a class hierarchy has a uniform signature for the constructors of its subclasses.

Consider:

public class ColorPencil extends Pencil
{
    private Color color;

    public ColorPencil(Color color)
    {
        super();
        this.color=color;
    }   
}

This makes ColorPencil a valid T (it extends Item). However, there is no no-arg constructor for this type. Hence, T() is nonsensical.

To do what you want, you need to use reflection. You can't benefit from compile-time error checking.