[sireesha]

Hi,i wrote code for stack operations.
I pasted that code below,

Code:

import java.io.*;
class Stack
{
 int i;
 int[] st;
 
 public Stack(int size)
 {
   st=new int[size];
   i=-1;
 }
 public void push()throws IOException
 {
  i++;
  BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  System.out.print("Enter a element:");
  st[i]=Integer.parseInt(br.readLine());
  
 } 
 public void pop()
 {
   if(i<0)
    System.out.println("Stack is empty.");
   else
  {
    i--;
   System.out.print("Last entered number is deleted.");
  }
 }
 public void checkempty()
 {
  if(i<0)
   System.out.println("Stack is empty.");
  else
   System.out.println("Stack is not empty.");
  }
  public void noofelements()
  {
   System.out.println("Number of elements in the Stack :"+(i+1));
  }
  public void printelements()
  {
   
   if(i<0)
    System.out.println("Stack is empty.");
   else
    {
      System.out.println("Stack elements are :");  
      for(int j=0;j<=i;j++)
        System.out.println(st[i]+" ");
     }
  }
}


class StackOperations
{
 public static void main(String[] args)throws IOException
 {
  int a,size;
  String check;
  BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

  System.out.print("Enter the length of the stack:");
  size=Integer.parseInt(br.readLine());

  Stack stobject=new Stack(size);

  System.out.println("This program is to perform stack operations.\n");
  System.out.println("Options for each operation;");
  System.out.println("1.insertion.");
  System.out.println("2.deletion.");
  System.out.println("3.to check stack is empty or not.");
  System.out.println("4.to print number of elements in stack.");
  System.out.println("5.to print stack elements.");
  do
  {
   System.out.print("\nEnter Your option:");
   a=Integer.parseInt(br.readLine());
   System.out.print("\n");
   switch(a)
   {
    case 1:  //insertion.
    {
      stobject.push();break;
    }
    case 2:  //deletion.
    {
      stobject.pop();break;
    }
    case 3:  //check empty.
    {
      stobject.checkempty();break;   
    }
    case 4:  //stack elements number.
    {
     stobject.noofelements();break;
    }
    case 5:  //to print stack elements. 
    {
     stobject.printelements();break;
    }
   }
   System.out.print("\nDo you want to continue(Enter yes/no) :");
   check=br.readLine();
  }while(check=="yes");
 }
}

With the above program i didn't get any errors.
But even though i entered yes for checking do-while loop,it comes out of the loop.
Is there any mistake in my code ?
And was i followed correct way to insertion, deletion and also for all other methods ?