How to create a generic stack (whose elements can be of any data types) ???

Question

How do you define a "Stack" class that takes the Data type as its constructor argument ,and creates a new instance of that stack type ??? e.g. Stack("double") should create a stack of doubles ,and so on...
     Putting it in another way, how do you go about defining a Stack ,if you are not sure what data types will be pushed into it at runtime ??? Making a Stack of Objects doesn't seem the appropriate choice since, in that case also, you won't be sure of which of the "parseInt(),paresDouble(),Integer(),Double() etc." functions to retrieve the value.

Answer 1

Write your own stack class which delegates push and pop calls to an internal instance of the java.util.Stack. In addition the class has an attribute of type Class. When the push method is invoked the object in the argument will be tested whether it is an instance of the class stored in the type attribute. If not an IllegalArgumentException should be thrown.
Here is the minimal code for such a type-save stack (the main method shows its usage):
import java.util.Stack;
public class TypeSaveStack {
    private Stack _stack = new Stack();
    private Class _type;
    public TypeSaveStack(Class type) {
        _type = type;
    public void push(Object element) {
        if (_type.isInstance(element)) {
            _stack.push(element);
        } else {
            throw new IllegalArgumentException(element
                              + " is not an instance of " + _type);
    public Object pop() {
        return _stack.pop();
    public static void main(String[] args) {
        TypeSaveStack doubleStack = new TypeSaveStack(Double.class);
        doubleStack.push(new Double(Math.PI));
        System.out.println(doubleStack.pop());
        try {
            doubleStack.push("foo");
        } catch (Exception e) {
            System.out.println(e);
}