infix to postfix

class infix_to_postfix
{
  public static void main(String[] args)
  {
     String input="1+2*4/5-7+3/6";
     infix_to_postfix object=new infix_to_postfix();
     intopost(input);
  }
  static String input="1+2*4/5-7+3/6";
  static int l=input.length();
  static char array[]=new char[l];
  static int top=-1;
  
  static int precedence(char ch)
  {
    if(ch=='+' || ch=='-')
    {
      return 1;
    }
    if(ch=='/' || ch=='*')
    {
      return 2;
    }
    if(ch=='^')
    {
      return 3;
    }
    return -1;
  }

  public static void push(char ch)
  {
      top++;
      array[top]=ch;
  }
  
   public static void pop()
  {
       System.out.print(array[top]);
       top--;      
  }
  
   public static char peek()
  {
      return array[top];     
  }
  
   public static boolean isempty()
  {
    if(top==-1)
    {
      return true;  
    }
    return false;
  }
  
  
  static void intopost(String input)
  {
     for (int j = 0; j < input.length(); j++) 
     {
         char ch = input.charAt(j);
         if((ch>='a'&&ch<='z')||(ch>='0' &&ch<='9') || (ch>='A' && ch<='Z') )
         {
           System.out.print(ch);
         }
         else if(ch=='+' || ch=='-' || ch=='*' || ch=='/' || ch=='^' )
         {
          
            if(top==-1)
              {
                  push(ch);
              }
            else
            {
                        while(precedence(ch)<=precedence(array[top]) )
                        {
                           pop();
                           if(top==-1)
                           {
                               break;
                           }
                        }

                        push(ch);
            }
         }
         else if(ch=='(')
         {
           push(ch);
         }
         else if(ch==')')
         {
           while(!(peek()=='(' ) )
           {
             pop();
            }
         }
  
      }
      
      while(!isempty())
      {
      pop();
      }
    }

}