// This is how a class is defined to take in objects of
// so-called generic types. That is, the class definition
// uses a generic type (that we call StackDataType). At compile time,
// MyStack can be compiled without knowing what types will actually 
// be used. 

class MyStack <StackDataType> {

    // This is now an array of the generic type.
    StackDataType [] stack;

    int stackTop;
    
    public void initialize ()
    {
        // Arrays of generic types cannot be instantiated directly
        // in Java. This is the workaround.
        stack = (StackDataType[]) new Object [100];
    }
    

    // Note: the parameter is now of the generic type.

    public void push (StackDataType value)
    {
        stack[++stackTop] = value;
    }
    

    // Note: the return value is now of the generic type.

    public StackDataType pop ()
    {
        StackDataType value = stack[stackTop];
        stackTop --;
        return value;
    }
    
    public boolean isEmpty ()
    {
        if (stackTop < 0) {
            return true;
        }
        else {
            return false;
        }
    }

}


public class StackExample4 {

    public static void main (String[] argv) 
    {
        // Now MyStack can be defined to accept only String's.
        MyStack<String> stack = new MyStack<String> ();
        stack.initialize ();

        stack.push ("Alice");
        stack.push ("Bob");
        stack.push ("Chen");
        
        while (! stack.isEmpty ()) {
            // No cast required.
            String name = stack.pop ();
            System.out.println ("Removed " + name);
        }
        
    }
    
}