Programming With Interface

��: Holub on Patterns by Allen Holub

��는 말��. 많�� 들�� 보��는 �� ... ��! ��. �� 무�� 를 보�� 못��.
�� '��~ �� 는데? �� Base �� 만들�� 는데?' ��말�� . �� 는 ��를 ��. '��~! �� 끔�� 는��?' ��만 ��. �� 먼�� 동��들�� . �� . Base �� 부��... �� 는��. �� 들�� 미��. ��말 미��. ��런 �� 는 �� 를 높��. �� ..! 동�� 는��? ��를 ��는데 �� 리�� 마�� 는 ��...
�� 는 �� . �� 능�� 100%�� 면�� 능�� 는 �� ! .. ��런 �� 는 �� . GoF�� 른 DP�� 들�� 말��. �� 보��는 ��를 �� ... �� 를 �� . 동�� 는��? Base ��를 �� 마�� 를 �� 는 �� 면 �� 를 �� 는�� 더 낫��는 ��. ��는 �� SRP (Single Responsiblity Principle)�� .

Holub�� 는 ��를 보��. �� Stack�� .

class Stack extends ArrayList {

 private int topOfStack = 0;

 

 public void push(Object article) {

  add(topOfStack++, article);

 }

 

 public Object pop() {

  return remove(--topOfStack);

 }

 

 public void pushMany(Object[] articles) {

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

   push(articles[i]);

 }

}

��벽�� Stack��. ��만 �� 를 ��면 ��리는 Stack �� 떻�� 돌�� .

Stack aStack = new Stack();

stack.push("1");

stack.push("2");

stack.clear(); // ??? ArrayList��� 메�����������...;;

�� 모�� clear 를 �� 는데 topOfStack�� 3�� . �� 문��를 �� . �� 면 �� 는 �� 메�� 는 ��.

�� 는 메�� 면 모�� 딩��는 방�� 만 만�� 많�� 메�� 면 �� 릴 ��. ��리�� 만�� 면 �� . �� 른 방�� 를 ��딩�� 를 �� 만들�� 는 �� 막�� . ��만 ��는 �� 러를 런�� 러�� 바��는 ��. ��리�� LSP (Liskov Sustitution Principle : "�� 는 �� 대�� 능�� ") �� . �� ArrayList를 ��받�� Stack�� clear 메��를 �� . ��런데 ��를 �� 말�� 는��?

Stack�� 는 ��른 방�� 대�� 를 ��는 ��.

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();

 }

}

��.. Stack�� ArrayList�� 많�� 낮�� . �� clear 따�� 는��. �� 는 방�� 더 �� . ��런 말�� . �� 보��는 �� ... �� 본�� 들�� Stack�� 는 ��를 만들�� 보��. MonitorableStack�� Stack�� , ��대 ��를 ��는 Stack��.

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; }

}

��끔�� . ��만 MonitorableStack�� pushMany ��를 ��. MonitorableStack�� pushMany ��를 ��면 MonitorableStack�� 받�� articles�� articles.length 만�� push�� . ��만 �� push 메��는 MonitorableStack�� 는 ��! 매번 size() ��를 �� 대 ��를 ��. �� 느�� . ��리�� 만�� Stack�� 를 보�� pushMany �� 문�� Stack�� 면 ��떻�� ???

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;

 }

}

��!~ �� Stack보�� 능�� . ��런데 문�� . 더�� pushMany 메�� push 메��를 �� 는��. �� 면 MonitorableStack�� 더�� Stack�� 대 ��를 �� 못�� . �� . �� 문��. �� (�� 내��) ��면, ��마 '�� 번 더 ��는�� ' ��는 �� 느�� . ��면 �� 는 ��...

�� . �� 를 보��. �� 말�� 보��는 ��... ��보��는 ��를... ��란 말�� 면 ...

"��(��)�� 를 ��." ��는 �� .

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(); }

}

�� 는 �� 문��들�� 는��.