java - Creating queue from two stacks -

can explain doing wrong here ? trying create queue 2 stacks per book exercise. error "stack underflow" peek function. seems right me :p please explain. thanks!

//program implement queue using 2 stacks.  import java.util.nosuchelementexception;  public class ex3_5_stack {     int n;     int countofnodes=0;     private node first;      class node {         private int item;         private node next;     }      public ex3_5_stack() {         first=null;         n=0;     }      public int size() {         return n;     }      public boolean isempty() {         return first==null;     }      public void push(int item){         if (this.countofnodes>=3) {             ex3_5_stack stack = new ex3_5_stack();             stack.first.item=item;             n++;         } else {             node oldfirst = first;             first = new node();             first.item=item;             first.next=oldfirst;             n++;         }     }      public int pop() {         if (this.isempty())              throw new nosuchelementexception("stack underflow");          int item = first.item;         first=first.next;         return item;     }      public int peek() {         if (this.isempty())              throw new nosuchelementexception("stack underflow");          return first.item;     } } 

and myqueue file

public class ex3_5_myqueue {     ex3_5_stack stacknewest,stackoldest;      public ex3_5_myqueue() {         super();         stacknewest = new ex3_5_stack();         stackoldest = new ex3_5_stack();     }      public int size() {         return stacknewest.size()+stackoldest.size();     }      public void add(int value) {         stacknewest.push(value);     }      private void transferstack() {         if (stackoldest.isempty()) {             while (stacknewest.isempty()) {                 stackoldest.push(stacknewest.pop());             }         }     }      public int peek() {         this.transferstack();         return stackoldest.peek();     }      public int remove() {         this.transferstack();         return stackoldest.pop();     }      public static void main(string[] args) {         ex3_5_myqueue myqueue = new ex3_5_myqueue();         myqueue.add(4);         myqueue.add(3);         myqueue.add(5);         myqueue.add(1);         system.out.println(myqueue.peek());     } } 

in transferstack(), you're missing exclamation mark. should be:

private void transferstack(){     if(stackoldest.isempty()){         while(!stacknewest.isempty()){ // forgot here             stackoldest.push(stacknewest.pop());         }     } }