Re: about the Object reference

"Martin Lansler" <>
Fri, 28 Jul 2006 11:05:25 GMT
You can check if an object is of a certain type using 'instanceof'.

if (o instanceof String) {
    String s = (String) o;

however it would be better if you designed the Stack with generics.

 * A stack
 * @param <T> the generic type
public interface Stack<T> {
     * Push an object onto the stack
     * @param t the object
    void push(T t);

     * @return pop an object from the stack
    T pop();

A simple implementation used a linked list:

import java.util.LinkedList;

 * Implementation of Stack
public class StackImpl<T> implements Stack<T> {
    private LinkedList<T> list = new LinkedList<T>();

     * {@inheritDoc}
    public T pop() {
        return list.removeLast();

     * {@inheritDoc}
    public void push(T t) {

Example usage:

public class StackTest {
    public static void main(String[] args) {
        Stack<String> stack = new StackImpl<String>();


"jtl.zheng" <> wrote in message

I have write a stack which have interfaces:

------- public void push(Object o);
------- public Object pop();

then I can push any type class object into the stack
and when I pop() one element I can use:

------- Object o=pop();
------- o.getClass();

to determine this element o belong to what class
(eg. if it's String it return "class java.lang.String")

my question is when I know this o is a String Object
how can I use its String interface
something like:

------- Object o=pop();
------- String s=o; // can't compiled here
                              // java.lang.Object, required:
------- System.out.println(s.charAt(n)); // use the String

I know this o is point to a String object
how can I use this o's String interface (to get something like
o.charAt(n)) ?

Thank you very much in advance

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