objects in java

cwl157 · 02-25-2005, 09:28 PM

I need to make a calculator in java but in an object oriented way. In the end it is supposed to take a user inputted expression as a string and solve the expression just left to right ignoring any order of operations. I am trying to make the first object which is a number object. I get 2 compiling errors one says identifier expected in line 6 and the other says im missing a curling brace on line 82 ( the end of the class). Can someone help me out and tell me how i am constucting it wrong. And also if you can tell me if this will work when i implement it in another class. I really have little idea of what im doing.
Here is the code:

Code:

import java.util.*;
import java.io.*;
public class Number
{
  int numExp = Number.getInput();

  Number(int numExp)
  {
    this.doOperation(Exper);
  }
  
  //gets a single input from the user, and returns it as a String
 static String getInput()
 {
  java.io.InputStreamReader input = new java.io.InputStreamReader(System.in);
  java.io.BufferedReader console = new java.io.BufferedReader(input);

  try
  {
   return console.readLine();
  }
  catch(java.io.IOException e)
  {
   System.err.println("Bad NEWS!!!");
   return "";
  }
 }

  //Uses the StringTokenizer to break up the numeric experession and sends the tokens to the performOperation method
 static int doOperation(String Exper)
 {
  int result=0; int num =0; String operation ="";
  StringTokenizer numEx = new StringTokenizer(Exper, "+-/%*", true);
  result = Integer.parseInt(numEx.nextToken());
  if(!numEx.hasMoreTokens())
  {
  return result;
  }
  do
  {
   operation = numEx.nextToken();
   num = Integer.parseInt(numEx.nextToken());
   result = Calculator1.performOperation(result, num, operation);
  }while(numEx.hasMoreTokens());
  return result;
 }

  //performs the operation op on num1 and num2 returning the result as an int to result int the doOperation class
 static Number performOperation(Number num1, Number Exper, Operator op)
 {
  if(op.equals("+"))
  {
   return num1 + num2;
  }
  else if(op.equals("-"))
  {
   return num1 - num2;
  }
  else if(op.equals("*"))
  {
   return num1 * num2;
  }
  else if(op.equals("/"))
  {
   return num1 / num2;
  }
  else if(op.equals("%"))
  {
  return num1 % num2;
  }
 else
 {
  System.err.println("Not an operation: " + op);
  return -1;
 }
 }

  static int getValue(number a)
  {
    int result = (int) a;
    return result;
  }
}

cwl157 · 02-25-2005, 09:37 PM

ok so i looked more closely at the code i posted and realized a lot of stupid mistakes. So now i really have no idea where to start. I have a plan that is correct but i have no idea where to start the implementation. I have a program that does this but its all in one class and i have no clue how to break it up. Can someone please give me some direction? Thanks

cwl157 · 02-26-2005, 05:22 PM

I think what im really confused about is building the constructors. I completed the first class which is called number all except for the constructor. What do i put in the constructor to make it create all those methods or whatever? Here is the number class without a constructor can someone help me built a contructor for it?

Code:

import java.io.*;
import java.util.*;

public class Number
{
    
 //gets a single input from the user, and returns it as a String
 static String getInput()
 {
  java.io.InputStreamReader input = new java.io.InputStreamReader(System.in);
  java.io.BufferedReader console = new java.io.BufferedReader(input);

  try
  {
   return console.readLine();
  }
  catch(java.io.IOException e)
  {
   System.err.println("Bad NEWS!!!");
   return "";
  }
 }
 
 //Uses the StringTokenizer to break up the numeric experession and sends the tokens to the performOperation method
 static int doOperation(String Exper)
 {
  int result=0; int num =0; String operation ="";
  StringTokenizer numEx = new StringTokenizer(Exper, "+-/%*", true);
  result = Integer.parseInt(numEx.nextToken());
  if(!numEx.hasMoreTokens())
  {
  return result;
  }
  do
  {
   operation = numEx.nextToken();
   num = Integer.parseInt(numEx.nextToken());
   result = Number.performOperation(result, num, operation);
  }while(numEx.hasMoreTokens());
  return result;
 }
 
 //performs the operation op on num1 and num2 returning the result as an int to result int the doOperation class
 static int performOperation(int num1, int num2, String op)
 {
  if(op.equals("+"))
  {
   return num1 + num2;
  }
  else if(op.equals("-"))
  {
   return num1 - num2;
  }
  else if(op.equals("*"))
  {
   return num1 * num2;
  }
  else if(op.equals("/"))
  {
   return num1 / num2;
  }
  else if(op.equals("%"))
  {
  return num1 % num2;
 }
 else
 {
  System.err.println("Not an operation: " + op);
  return -1;
 }
 }
}

cwl157 · 02-26-2005, 09:57 PM

o so now i think i have all the objects written. However, when i run it in NetBeans IDE it compiles and runs fine. But if i try to run it in the command line it gives a nosuchelement exception. Does anyone know why it runs ok in netbeans but not in the command line? Here are the classes

Number class

Code:

import java.io.*;
import java.util.*;

public class Number
{
    Number()
    {
    }
    
 //gets a single input from the user, and returns it as a String
 String getInput()
 {
  java.io.InputStreamReader input = new java.io.InputStreamReader(System.in);
  java.io.BufferedReader console = new java.io.BufferedReader(input);

  try
  {
   return console.readLine();
  }
  catch(java.io.IOException e)
  {
   System.err.println("Bad NEWS!!!");
   return "";
  }
 }
 
  int getValue(String result)
    {
        Operator o = new Operator();
        int num = 0;
        String check = "";
        StringTokenizer tok = new StringTokenizer(this.getInput());
        do
        {
           check = tok.nextToken();
           if(!check.equals("+") || !check.equals("-") ||!check.equals("*") || !check.equals("/") || !check.equals("%"))
              num = Integer.parseInt(check);
           else
               o.getOp(result);
        }while(tok.hasMoreTokens());
        
        return num;
    }
 
 
 //Uses the StringTokenizer to break up the numeric experession and sends the tokens to the performOperation method
 int doOperation(String Exper)
 {
  int result=0; int num =0; String operation ="";
  StringTokenizer numEx = new StringTokenizer(Exper, "+-/%*", true);
  result = Integer.parseInt(numEx.nextToken());
  if(!numEx.hasMoreTokens())
  {
  return result;
  }
  do
  {
   operation = numEx.nextToken();
   num = Integer.parseInt(numEx.nextToken());
   result = Number.performOperation(result, num, operation);
  }while(numEx.hasMoreTokens());
  return result;
 }
 
 //performs the operation op on num1 and num2 returning the result as an int to result int the doOperation class
   static int performOperation(int num1, int num2, String op)
   {
    if(op.equals("+"))
    {
      return num1 + num2;
    }
    else if(op.equals("-"))
    {
     return num1 - num2;
    }
   else if(op.equals("*"))
   {
     return num1 * num2;
   }
  else if(op.equals("/"))
  {
   return num1 / num2;
  }
    else if(op.equals("%"))
   {
     return num1 % num2;
  }
  else
  {
   System.err.println("Not an operation: " + op);
   return -1;
  }
 }
}

Operator class

Code:

import java.io.*;
import java.util.*;

public class Operator
{
     Number t = new Number();
    String result = t.getInput();
    
    Operator()
    {
        this.getOp(result);
    }
    
    char getOp(String result)
    {
        char op = '+';
        String check = "";
        StringTokenizer tok = new StringTokenizer(t.getInput());
        do
        {
           check = tok.nextToken();
           if(check.equals("+"))
               op = '+';
           if(check.equals("-"))
               op = '-';
           if(check.equals("*"))
               op = '*';
           if(check.equals("/"))
               op = '/';
           if(check.equals("%"))
               op = '%';
        }while(tok.hasMoreTokens());
        
        return op;
    }
}

CalculatorOO class with main method

Code:

import java.io.*;
import java.util.*;

public class CalculatorOO
{
    public static void main(String args[])
    {
        String cont = "";
        Number n = new Number();
        StringTokenizer result = new StringTokenizer(n.getInput());
        Operator op = new Operator();
        
        do
        {
          String exp = n.getInput();
          System.out.println(op.getOp(exp));
          System.out.println(n.getValue(exp));
        }while(result.hasMoreTokens());
         do
        {
         System.out.println("Please enter a numeric expression: ");
         System.out.print("Do you want to enter another expression (y/n): ");
         cont = n.getInput();
        }while(cont.equalsIgnoreCase("y"));
        System.out.println("Goodbye");
    }
}