why we cannot use "new T()" in constractor method

最近在整理进入职业生涯后的技术学习路线，看到一个实现栈功能的类，贴出来，如下：

public class Stack<T> {
    private static final int DEFAULT_CAPACITY = 10;

    private T[] elements;
    private int size;

    Stack() {
        elements = new T[DEFAULT_CAPACITY];
    }
}publi