Programming With Interface

class Stack {

 private int topOfStack = 0;

 private ArrayList theData = new ArrayList();

 

 public void push(Object article){

  theData.add(topOfStack++, article);

 }

 

 public Object pop() {

  return theData.remove(--topOfStack);

 }

 

 public void pushMany(Object [] articles) {

  for(int i=0; i<articles.length; ++i)

   push(articles[i]);

 }

 

 public int size() {

  return return theData.size();

 }

}

class MonitorableStack extends Stack {

 private int maxHeight = 0;

 private int minHeight = 0;

 

 public void push(Object o) { 

  push(0);

  if(size() > maxHeight)

   maxHeight = size();

 }

 

 public Object pop() {

  Object poppedItem = pop();

  if(size() < minHeight)

   minHeight = size();

  return poppedItem;

 }

 

 public int maximumSize() { return maxHeight; }

 public int minimumSize() { return minHeight; }

}

class Stack {

 private int topOfStack = -1;

 private Object[] theData = new Object[1000]; 

 public void push(Object article) {

  theData[++topOfStack] = article;

 }

 

 public Object pop() {

  Object popped = theData[topOfStack--];

  theData[topOfStack] = null;

  return popped; 

 }

 

 public void pushMany(Object [] articles) {

  assert((topOfStack + articles.length) < theData.length);

  System.arraycopy(articles, 0, theData, topOfStack + 1, articles.length);

  topOfStack += articles.length;

 }

 

 public int size() {

  return topOfStack + 1;

 }

}

interface Stack {

 void push(Object article);

 Object pop();

 void pushMany(Object [] articles);

 int size();

}

 

class SimpleStack implements Stack {

 private int topOfStack = 0;

 private ArrayList theData = new ArrayList();

 

 public void push(Object article){

  theData.add(topOfStack++, article);

 }

 

 public Object pop() {

  return theData.remove(--topOfStack);

 }

 

 public void pushMany(Object [] articles) {

  for(int i=0; i<articles.length; ++i)

   push(articles[i]);

 }

 

 public int size() {

  return return theData.size();

 } 

}

 

class MonitorableStack implements Stack {

 private int maxHeight = 0;

 private int minHeight = 0;

 private SimpleStack stack = new SimpleStack(); 

 

 public void push(Object o) { 

  stack.push(0);

  if(stack.size() > maxHeight)

   maxHeight = size();

 }

 

 public Object pop() {

  Object poppedItem = stack.pop();

  if(size() < minHeight)

   minHeight = stack.size();

  return poppedItem;

 }

 

 public void pushMany(Object [] articles) {

  for(int i=0; i<articles.length; ++i)  

   push(articles[i]);

 

  if(stack.size() > maxHeight)

   maxHeight = stack.size();  

 }

 

 public int maximumSize() { return maxHeight; }

 public int minimumSize() { return minHeight; } 

 public int size() { stack.size(); }

}