How to write this program efficiently and much shorter?

Question

How to optimize below code to reduce code with better performance?

import java.util.Scanner;

public class ConsoleCalculatorImproved 
{
    static boolean ERROR = true;
    public static void main(String[] m)
    {
        String arg ;
        ConsoleCalculatorImproved cC = new ConsoleCalculatorImproved();
        CalculatorMain cM = cC.new CalculatorMain();
        float result;
        Scanner cInput = new Scanner(System.in);
        try
        {
            arg = m[0];
        }
        catch(ArrayIndexOutOfBoundsException e)
        {
            System.out.println("Enter Expression : ");
            arg = cInput.nextLine();
        }
        result = cM.evaluateExpression(arg);
        if(ERROR == false) 
        System.out.println(arg+" = "+result);
    }
    class CalculatorMain
    {
        String expression;
        StringBuilder numExtractor;
        float result,temp;
        int opCount;
        char operator,current;
        public CalculatorMain()
        {
            expression = new String();
            numExtractor = new StringBuilder();
            numExtractor.setLength(10);
            opCount =  0;
            result = temp = 0;
            operator = current = 0;
        }
        public boolean isDigit(char test)
        {
            if(test >='0' && test <='9') return true;
            else return false;
        }
        public float evaluateExpression(String exp)
        {
            expression = exp.trim();
            expression = "("+expression+")";
            int i,sc=0;
            for(i=1;i<expression.length();i++)
            {
                current = expression.charAt(i);
                if(i == 1)
                {
                    if(isDigit(current)||current=='-')
                        numExtractor.setCharAt( sc++ , current );
                    else if(current == '(')
                    {
                        if(expression.indexOf(')') != expression.lastIndexOf(')'))
                        {
                            CalculatorMain cm = new CalculatorMain();
                            String Temporary = expression.substring(2,expression.indexOf(')'));
                            result = cm.evaluateExpression(Temporary);
                            i = expression.indexOf(')');
                            StringBuilder t = new StringBuilder(expression);
                            t.setCharAt(expression.indexOf(')'),'x');
                            expression = t.toString();
                        }
                        else
                        {
                            System.out.println("ERROR : Pair of Brackets Expected");
                        }
                    }
                    else
                    {
                        System.out.println("ERROR : Invalid Expression !");
                        return result;
                    }
                }
                else if( ( expression.charAt(i-1) != 'x' ) && ( current == ')' ))
                {
                    if(opCount == 0)
                    {
                        result = Float.parseFloat(numExtractor.toString());
                        break;
                    }
                    else
                    {
                        temp = Float.parseFloat(numExtractor.toString().trim());
                        switch(operator)
                        {
                            case'+': result+=temp;break;
                            case'-': result-=temp;break;
                            case'*': result*=temp;break;
                            case'/': result/=temp;break;
                        }
                        break;
                    }
                }
                else if( ( expression.charAt(i-1) == 'x' ) && ( current == ')' ))
                {
                    break;
                }
                else
                {
                    if(isDigit(current) || (current == '.') )
                    {
                        numExtractor.setCharAt( sc++ , current);
                    }
                    else if(current == '-' && ( expression.charAt(i-1) == '+' || expression.charAt(i-1) == '-' || expression.charAt(i-1) == '*' || expression.charAt(i-1) == '/' ))
                    {
                        numExtractor.setCharAt( sc++ , current);
                    }
                    else
                    {
                        if((expression.charAt(i-1)!='x')&&(current == '+' || current == '-' || current == '*' || current == '/'))
                        {   
                            if(opCount==0)
                            {
                                result = Float.parseFloat(numExtractor.toString().trim());
                                numExtractor = new StringBuilder();
                                numExtractor.setLength(10);
                                sc = 0;
                                opCount++;
                                operator = current;
                            }
                            else
                            {
                                temp = Float.parseFloat(numExtractor.toString().trim());
                                numExtractor = new StringBuilder();
                                numExtractor.setLength(10);
                                sc = 0;
                                switch(operator)
                                {
                                    case'+': result+=temp;break;
                                    case'-': result-=temp;break;
                                    case'*': result*=temp;break;
                                    case'/': result/=temp;break;
                                }
                                operator = current;
                                temp = 0;
                                opCount++;
                            }
                        }
                        else if((expression.charAt(i-1)=='x')&&(current == '+' || current == '-' || current == '*' || current == '/'))
                        {
                            opCount++;
                            operator = current;
                        }
                        else if(current == '(')
                        {
                            if( opCount !=0 && (expression.indexOf(')') != expression.lastIndexOf(')')))
                            {
                                CalculatorMain cm = new CalculatorMain();
                                String Temporary = expression.substring(i+1,expression.indexOf(')'));
                                temp = cm.evaluateExpression(Temporary);
                                i = expression.indexOf(')');
                                StringBuilder t = new StringBuilder(expression);
                                t.setCharAt(expression.indexOf(')'),'x');
                                expression = t.toString();
                                switch(operator)
                                {
                                    case'+': result+=temp;break;
                                    case'-': result-=temp;break;
                                    case'*': result*=temp;break;
                                    case'/': result/=temp;break;
                                }
                            }
                            else if(opCount == 0)
                            {
                                System.out.println("ERROR : Missing Operator before Bracket");
                                return result;
                            }
                            else
                            {
                                System.out.println("ERROR : Pair of Brackets Expected");
                            }
                        }
                        else
                        {
                            System.out.println("Invalid Expression!");
                            return result;
                        }
                    }
                }
            }
            ERROR = false;
            return result;
        }
    }
}

Answer 1

You need to compile and interpret a programming language, even though your language is rather simple expression language. Write recursive descent parser or use ANTLR.

Answer 2

You should consider using Parboiled. It allows you to write grammars entirely in Java.

As a bonus, it has a calculator example, complete with parens etc.

I know ANTLR is generally the name that comes first; but the fact that Parboiled does not require that you "precompile" your grammars is a HUGE bonus.

Answer 3

You should read about the Shunting-yard algorithm. It can be used to parse mathematical expressions in the normal (infix) notation into postfix notation (or Reverse Polish Notation), which can then be evaluated easily (and efficiently).