Infix to Postfix and evaluate

[ddp]

I know how to convert to infix to postfix but cant evaluate the result please help

import java.util.*;
class term
  {public term next;
    public Object data;
   public term() 
     {data=' ';
     next=null; 
     }
    public term(Object val) 
       {data = val; 
         next = null;
      }
 }
public class intopost
   {private term top;
       public intopost(){top = null;}
      public boolean empty(){ return top == null; }
      public boolean full(){return false;}
      public void push(Object e){
        term tmp = new term(e);
        tmp.next = top;
        top = tmp;
    }
public Object pop()
    {Object e =  top.data;
    top = top.next;
    return e;
    }
public Object peek()
   {Object e=top.data;
    return e;
    }
public void matching(String x)
    {Stack s=new Stack();
     for(int i=0;i<x.length();i++)
        {char c=x.charAt(i);
            if(c=='(')
                s.push(c);
            else
            {if(c==')')
                if(s.empty())
                    matching=false;
                else
                    s.pop();
            }
        }
        if(!s.empty())
            matching=false;
    }
public void Evaluation(String x)
{int i,z,u;
 char c;  
    intopost S=new intopost();
    for(i=0;i<x.length();i++)
       {c=x.charAt(i);
        String s="0"+c;
       
        if(c=='+')
           {
            z=Integer.parseInt((String)S.pop())+Integer.parseInt((String)S.pop());
            S.push(Integer.toString(z));
           }
        else if(c=='*')
           {
            z=Integer.parseInt((String)S.pop())*Integer.parseInt((String)S.pop());
            S.push(Integer.toString(z));
           }
        else if(c=='/')
           {u=Integer.parseInt((String)S.pop());
            z=Integer.parseInt((String)S.pop())/u;
            S.push(Integer.toString(z));
            }
        else if(c=='-')
            {u=Integer.parseInt((String)S.pop());
             z=Integer.parseInt((String)S.pop())-u;
            S.push(Integer.toString(z));
            }
        else
            S.push(s);
    }
    System.out.println("THE POSTFIX = "+x);
    System.out.println("THE RESULT = "+S.pop());
}
public String postfix(String x)
{
    String output="";
    intopost S=new intopost();
    for(int i=0;i<x.length();i++)
    {char c=x.charAt(i);
       if(c==('+')||c==('*')||c==('-')||c==('/'))
            {while(!S.empty() && priority(S.peek())>= priority(c))
                output+=S.pop();
            S.push(c);
            }
        else if(c=='(')
             S.push(c);
        else if(c==')')
        { while(!S.peek().equals('('))
            output+=S.pop();
            S.pop();
        }
        else
            output+=c;
    }
    while(!S.empty())
        output+=S.pop();
    return output;
}
public int priority(Object x)
{
    if(x.equals('+')||x.equals('-'))
        return 1;
    else if(x.equals('*')||x.equals('/'))
        return 2;
    else
        return 0;}   
public static boolean matching=true;
public static void main(String args[])
{   intopost e=new intopost();
     String infix,post;
     System.out.println("enter equation in ifix form");
     Scanner in=new Scanner(System.in);
     infix=in.next();
     post=e.postfix(infix);
     System.out.println("THE POSTFIX = "+post);
    e.matching(infix);
    e.Evaluation(infix);
   }
}