수다닷컴

인터페이스와 관련된 질문입니다.

스택관련 소스인데
제가 궁금한것은

인터페이스로 선언한 StackItem 을

Stack 클래스에서

StackItem top:

선언해서 사용하는데
흐름이 어떻게 되는지 궁금합니다.

인터페이스는 상속만 해서 사용하는 줄 알았는데...ㅡㅜ;;

무슨 뜻인지 설명해주시면 감사하겠습니다
interface StackItem
{
public StackItem getNextItem();
public void setNextItem(StackItem item);
}class Stack
{
StackItem top;
public Stack()
{
top = null;
}
public void push(StackItem item)
{
if (top == null)
{
top = item;
}
else
{
item.setNextItem(top);
top = item;
}
}
public StackItem pop()
{
if(top == null)
{
System.out.println(stack is empty);
java.lang.System.exit(-1);
}
StackItem topItem = top;
top = top.getNextItem();
return topItem;
}

public void printAll()
{
System.out.print(This stack has : );
StackItem item = top;

while(item != null)
{
System.out.print(item);
item = item.getNextItem();
}
System.out.println();
}
}
class IntItem implements StackItem
{
int i;
StackItem next;
public IntItem(int i)
{
this.i = i;
next = null;
}

public StackItem getNextItem()
{
return next;
}
public void setNextItem(StackItem item)
{
next = item;
}
public String toString()
{
return i+;
}
}
class StringItem implements StackItem
{
String s;
StackItem next;
public StringItem(String s)
{
this.s = s;
next = null;
}
public StackItem getNextItem()
{
return next;
}
public void setNextItem(StackItem item)
{
next = item;
}
public String toString()
{
return s;
}
}
class ComplexNumberItem implements StackItem
{
double real;
double imaginary;
StackItem next;
public ComplexNumberItem(double r, double i)
{
real = r;
imaginary = i;
next = null;
}
public StackItem getNextItem()
{
return next;
}
public void setNextItem(StackItem item)
{
next = item;
}
public String toString()
{
return real+++imaginary+i;
}
}
public class StackTest
{
public static void main(String[] args)
{
Stack aStack = new Stack();
aStack.push(new IntItem(10));
aStack.push(new StringItem(Kim));
aStack.push(new ComplexNumberItem(1, 5));
aStack.push(new ComplexNumberItem(2, 4));
aStack.push(new StringItem(lee));
aStack.push(new IntItem(9));
System.out.println(Item removed : + aStack.pop());
System.out.println(Item removed : + aStack.pop());
System.out.println(Item removed : + aStack.pop());
aStack.printAll();
}
}

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