Stacks

As mentioned in the introduction a stack would comprise of a collection of objects with various operations related to maintaining the collection. As an example a stack of strings could have the following operations associated.

//psuedo code
public class StackOfStrings()
  //create an empty stack
  StackOfStrings()
  //insert a new string into stack
  void push(String item)
  //remove eand return the string most recently added
  String pop()
  // is the stack empty?
  boolean isEmpty()
  // number of strings in the stack
  int size()

Lets write a simple client that takes some simple strings on standard input and some pop commands which are indicated with -

public static void main(String[] args){
  StackOfStrings stack = new StackOfStrings();
  while(!StdIn.isEmpty()){
    String s = StdIn.readString();
    if(s.equals("-")) StdOut.print(stack.pop());
    else stack.push(s);
  }
}