How do they do it? Generics and my own stack.

[dcoder]

Hello. I am going through the java tutorial online at the oracle website.

In the section about Generics, it states that you cannot create a Generic array. So the following code will work, but not the commented out store:



package HelloWorldPkg;

import java.util.Vector;

public class MyStack<T> {
// T[] store = new T[some_size]; // Does not work.
Vector<T> store = new Vector<T>();
int last = 0;

public MyStack() {
}

public void push( T t) {
store.add(t);
}

public T pop() {
return store.remove(store.size()-1);
}

public static void main( String[] args) {
MyStack<Integer> stack = new MyStack<Integer>();

stack.push(new Integer(3));
Integer i = stack.pop();

System.out.println( "Integer returned is: " + i);
return;
}
}

If I change the above code so that store is type T[] and I change push/pop accordingly, the java compiler complains about not being able to do new T[]. And that's because type erasure.

So how does one address this limitation (or limitation in my brain)?

So, to get around this, I changed store to Vector<T>.

but then, how does Vector<T> get around this problem?

I thought I could make store type Object[], but that eventually leads to an explicit cast to T, which is not allowed either due to type erasure.

Anyways, I'd like some enlightenment.

thanks!

[dcoder]

Here's a way I can get around it:


package HelloWorldPkg;

public class MyStack2<T> {
private class Pod<T> {
T t;
Pod<T> next;

Pod(T t) {
this.t = t;
this.next = null;
}
}

Pod<T> head = null;

void push(T t) {
Pod<T> oldhead = head;
head = new Pod<T>(t);
head.next = oldhead;
return;
}

T pop() {
T t = head.t;
head = head.next;
return t;
}

public static void main( String[] args) {
MyStack2<Integer> stack = new MyStack2<Integer>();

stack.push( new Integer(3));
Integer rval = stack.pop();
System.out.printf( "rval = %d\n", rval.intValue());
return;
}
}



But, I don't like the fact that internally it's a linked list. There's no way of creating a block of contiguous memory to create references to T?

thanks.