InFix.java

 

import java.util.EmptyStackException;

 

import java.util.Stack;

 

 

public class InFix

 

{

 

     Stack<String> operandsStk;

 

     Stack<Character> operatorsStk;

 

     InFix()

 

     {

 

 

 

          operandsStk=new Stack<String>();

 

          operatorsStk=new Stack<Character>();

 

     }

 

 

 

     public int evaluate(String exp) throws ArithmeticException

 

     {

 

          boolean fail=false;

 

          try

 

          {

 

              //Tokenize the string containing the expression while there are more tokens

 

          String tokens[]=exp.split(" ");

 

          for(int i=0;i<tokens.length;i++)

 

          {

 

              //if it is an operand push it onto the operand stack

 

              if(!tokens[i].equals("+")&& !tokens[i].equals("*")&&!tokens[i].equals("-")

 

&&!tokens[i].equals("/") && !tokens[i].equals("(")&&!tokens[i].equals(")"))

 

              {

 

                   operandsStk.push(tokens[i]);

 

              }

 

              //else if it is a left parenthesis

 

              else if(tokens[i].equals("("))

 

              {

 

                   //push it onto the operator stack

 

                   operatorsStk.push((Character)tokens[i].charAt(0));

 

              }

 

              //else if is a right parenthesis

 

              else if(tokens[i].equals(")"))

 

              {

 

                   //while top of the operator stack not a left parenthesis  

 

                   while(operatorsStk.peek()!='(')

 

                   {

 

                        // pop two operands and an operator

 

                        int x=Integer.parseInt(operandsStk.pop());

 

                        int y=Integer.parseInt(operandsStk.pop());

 

                        char opr=operatorsStk.pop();

 

                        //    perform the calculation  

 

                        int result=0;

 

                        if (opr=='+')

 

                        {

 

                             result= y+x;

 

                             //push the result onto the operand stack   

 

                             operandsStk.push(result+"");

 

                        }

 

                        else if(opr=='-')

 

                        {

 

                             result= y-x;

 

                             //push the result onto the operand stack

 

                             operandsStk.push(result+"");

 

                        }

 

                        else if(opr=='*')

 

                        {

 

                             result= y*x;

 

                             //push the result onto the operand stack

 

                             operandsStk.push(result+"");

 

                        }

 

                        else if(opr=='/')

 

                        {  

 

                             result=y/x;

 

                             //push the result onto the operand stack

 

                             operandsStk.push(result+"");

 

                        }

 

 

 

                   }

 

 

 

              }

 

              //else if it is an operator

 

              else if(tokens[i].equals("+")||tokens[i].equals("-")

 

                        ||tokens[i].equals("*")||tokens[i].equals("/"))

 

              {

 

                   //while the operator stack is not empty and the operator at the top of the stack has higher

 

                   //or the same precedence than the current operator

 

                   while(!operatorsStk.empty()&&hasHigherPrecedence(operatorsStk.peek(),tokens[i].charAt(0)))

 

                   {

 

                        //pop two operands

 

                        int x=Integer.parseInt(operandsStk.pop());

 

                        int y=Integer.parseInt(operandsStk.pop());

 

                        char opr=operatorsStk.pop();

 

                        //perform the calculation  

 

                        int result=0;

 

                        if (opr=='+')

 

                        {

 

                             result= y+x;

 

                             //push the result onto the operand stack

 

                             operandsStk.push(result+"");

 

                        }

 

                        else if(opr=='-')

 

                        {

 

                             result= y-x;

 

                             //push the result onto the operand stack

 

                             operandsStk.push(result+"");

 

                        }

 

                        else if(opr=='*')

 

                        {

 

                             result= y*x;

 

                             //push the result onto the operand stack

 

                             operandsStk.push(result+"");

 

                        }

 

                        else if(opr=='/')

 

                        {  

 

                             result=y/x;

 

                             //push the result onto the operand stack

 

                             operandsStk.push(result+"");

 

                        }

 

                   }

 

 

                   // Push the current operator on the operators stack

                   operatorsStk.push(tokens[i].charAt(0));

 

              }

 

          }

 

          //while the operator stack is not empty

 

          while(!operatorsStk.empty())

 

          {

 

              // pop two operands and an operator

 

              int x=Integer.parseInt(operandsStk.pop());

 

              int y=Integer.parseInt(operandsStk.pop());

 

              char opr=operatorsStk.pop();

 

              //perform the calculation

 

              int result=0;

 

              if (opr=='+')

 

              {

 

                   result= y+x;

 

                   // push the result onto the operand stack

 

                   operandsStk.push(result+"");

 

              }

 

              else if(opr=='-')

 

              {

 

                   result= y-x;

 

                   // push the result onto the operand stack

 

                   operandsStk.push(result+"");

 

              }

 

              else if(opr=='*')

 

              {

 

                   result= y*x;

 

                   // push the result onto the operand stack

 

                   operandsStk.push(result+"");

 

              }

 

              else if(opr=='/')

 

              {  

 

                   result=y/x;

 

                   // push the result onto the operand stack

 

                   operandsStk.push(result+"");

 

              }

 

          }

 

          }

 

          catch(EmptyStackException e)

 

          {       

 

              fail=true;

 

          }

 

          if(fail==false)

 

              //the final result is at the top of the operand stack

 

              return Integer.parseInt(operandsStk.pop());

 

          else

 

              return -1;

 

     }

 

     //returns true, if the top has high precedence than current

 

     boolean hasHigherPrecedence(char top, char current)

 

     {

 

          int topPre=-1;

 

          int curPre=-1;

 

          if(top == '+' || top == '-')

 

          {

 

              topPre=0;

 

          }

 

          if(top == '*' || top == '/' || top== '%')

 

          {

 

              topPre=1;

 

          }

 

          if(current == '+' || current == '-')

 

          {

 

              curPre=0;

 

          }

 

          if(current == '*' || current == '/' )

 

          {

 

              curPre=1;

 

          }

 

          if(topPre>=curPre)

 

              return true;

 

          else

 

              return false;

 

     }

 

 

GUI.java

 

import java.awt.FlowLayout;

 

import java.awt.GridLayout;

 

import java.awt.event.ActionEvent;

 

import java.awt.event.ActionListener;

 

import java.util.EmptyStackException;

 

import java.util.Stack;

 

import javax.swing.JButton;

 

import javax.swing.JFrame;

 

import javax.swing.JLabel;

 

import javax.swing.JOptionPane;

 

import javax.swing.JPanel;

 

import javax.swing.JTextField;

 

import javax.swing.SwingConstants;

 

public class GUI extends JFrame implements ActionListener

 

{

 

 

            private static final long serialVersionUID = 1L;

 

            JTextField userInput;

 

     JLabel input,result,hint;

 

     JPanel inputPanel,resultPanel;

 

     JButton evaluate;

 

     Stack<Object>stk;

 

     GUI()

 

     {

 

          //Main GUI

 

          super("Infix Expression Evaluator");

 

          inputPanel=new JPanel(new FlowLayout());

 

          resultPanel=new JPanel(new FlowLayout());

 

          setLayout(new GridLayout(2,1));

 

          userInput =new JTextField(30);

 

          hint=new JLabel("Example: ( 3 * 3 ) 7. Make sure to leave spacing. Use only (, ), +, -, * , / ");

 

          input=new JLabel("Enter Infix Expression:");

 

          evaluate=new JButton("Evaluate");

 

          evaluate.addActionListener(this);

 

          result=new JLabel("Result:",SwingConstants.LEFT);

 

          add(inputPanel);

 

          add(resultPanel);

 

          inputPanel.add(input);

 

          inputPanel.add(userInput);

 

          inputPanel.add(hint);

 

          inputPanel.add(evaluate);

 

          resultPanel.add(result);

 

          stk=new Stack<Object>();

 

     }

 

 

 

     public static void main(String args[])

 

     {

 

          GUI gui=new GUI();

 

          gui.setVisible(true);

 

          gui.setSize(500,300);

 

 

 

     }

 

 

     boolean isBalance(String exp)

 

     {

 

          int index = 0;

 

          boolean fail = false;

 

          int length=exp.length();

 

          try

 

          {

 

              while (index < length && !fail)

 

              {

 

                   char ch = exp.charAt(index);

 

                   switch(ch)

 

                   {

 

                        case '(':

 

                        stk.push( new Character(ch) );

 

                        break;

 

                        case ')':

 

                             char rightBrace=(char)stk.pop();

 

                             if(rightBrace!='(')

 

                                  fail=true;

 

                             break;

 

                        default:

 

 

 

                        break;

 

                   }

 

                   index++;

 

              }

 

          }

 

          catch(EmptyStackException e)

 

          {

 

              fail = true;

 

          }

 

          return stk.empty() && !fail;

 

     }

 

 

 

     public void actionPerformed(ActionEvent arg0)

 

     {

 

          InFix infix=new InFix();

 

 

 

              String expression=userInput.getText();

 

              //Call is evaluated if balance

 

              if(isBalance(expression))

 

              {

 

                   try

 

                   {

 

                        int answer=infix.evaluate(expression);

 

                        //Result display here

 

                        if(answer==-1)

 

                             result.setText("Result: Expresssion is not balanced.");

 

                        else

 

                             result.setText("Result: " +answer);

 

                   }

 

                   //Error message for dividing by 0

 

                   catch(ArithmeticException e)

 

                   {

 

                        JOptionPane.showMessageDialog(this, "You cannot divide by Zero. Try again!",

 

                                 "ERROR",

 

                                 JOptionPane.ERROR_MESSAGE);

 

                   }

 

              }

 

              //Error message if not balance

 

              else

 

                   result.setText("Result: Expresssion is not balanced.");

 

              userInput.setText("");

 

     }

 

}