Hi i keep receiving the error:

Exception in thread "main" java.util.EmptyStackException

at java.util.Stack.peek(Stack.java:85)

at java.util.Stack.pop(Stack.java:67)

at calc.Main.calculate(Main.java:147)

at calc.Main.main(Main.java:251)

Java Result: 1

I keep trying to google and read on how to fix it, but i deadlocked. Help pls?

Heres my code:

/* * To change this template, choose Tools | Templates * and open the template in the editor. */ package calc; import java.util.*; import jpb.*; public class Main { private integerStack myStack; private String infix; private String postfix = ""; //creates an empty stack used for declaring methods public Main(String in) { infix = in; int size = in.length(); myStack = new integerStack(size); } //method to convert infix expression to postfix expression public String convert() { for (int j = 0; j < infix.length(); j++) { char ch = infix.charAt(j); switch (ch) { case '+': case '-': checkPrecedence(ch, 1); break; case '*': case '/': checkPrecedence(ch, 2); // pop operators break; case '%': checkPrecedence(ch,3); break; case '(': myStack.push(ch); // push it break; case ')': parentheses(ch); // pop operators break; default: // must be an operand postfix = postfix + ch; // append to output break; } } while (!myStack.isEmpty()) { postfix = postfix + myStack.pop(); } System.out.println(postfix); return postfix; // return postfix } //method to order each operator encountered by the correct precedence public void checkPrecedence(char opThis, int p1) { while (!myStack.isEmpty()) { char opTop = myStack.pop(); if (opTop == '(') { myStack.push(opTop); break; } // it's an operator else { // precedence of new op int p2; if (opTop == '+' || opTop == '-') p2 = 1; else if (opTop=='*' || opTop=='/') p2=2; else p2=3; // if precendence of new op less than precendence of old save newly-popped op if (p2 < p1){ myStack.push(opTop); break; } //else append to postfix else postfix = postfix + opTop; } } myStack.push(opThis); } //method to grant expressions inside parentheses top precedence public void parentheses(char ch){ while (!myStack.isEmpty()) { char paren = myStack.pop(); if (paren == '(') break; else postfix = postfix + paren; } } //method to calculate postfix expression public static int calculate(String input) throws Exception { int finalResult; Stack <Integer> solution = new Stack<Integer>(); int op1,op2,result; for(int i=0;i<input.length();i++){ char c=input.charAt(i); try { switch (c){ case '+': op1=solution.pop(); op2=solution.pop(); result=op1 + op2; solution.push(result); break; case '-': op1=solution.pop(); op2=solution.pop(); result=op1 - op2; solution.push(result); break; case '*': op1=solution.pop(); op2=solution.pop(); result=op1 * op2; solution.push(result); break; case '/': op1=solution.pop(); op2=solution.pop(); result=op1 / op2; solution.push(result); break; case '%': op1=solution.pop(); op2=solution.pop(); result=op1 % op2; solution.push(result); break; default: solution.push(Integer.parseInt(Character.toString(c))); break; } } catch(EmptyStackException e){ System.exit(-1); } } finalResult = solution.pop(); return finalResult; } //method to check if number of operators is more than number of operands public static boolean checkOps(String input){ int countNumbers=0; int countOperators=0; for(int i=0;i<input.length();i++){ char ops=input.charAt(i); switch(ops){ case '+':case '-':case '*':case '/': case '%': countOperators++;break; default: countNumbers++; } } if(countNumbers<=countOperators) return false; else return true; } //method to check if infix contains floating point numbers. public static boolean checkFloat(String input){ char [] c=input.toCharArray(); for (int i=0;i<c.length;i++){ if (c[i]=='.'){ return false;} } return true; } //method to check if infix expression is in correct form public static boolean checkInfix(String input){ char[] c=input.toCharArray(); for(int i=0;i<c.length;i++){ if(Character.isDigit(c[i]) && Character.isDigit(c[i+1])){ return false; } else if (c[i]=='(' && !Character.isDigit(c[i+1])) return false; else return true; } return true; } public static void main(String[] args) throws Exception { while(true){ SimpleIO.prompt("Enter an infix expression to evaluate: \n"); String input = SimpleIO.readLine(); //if user enters float show error message and prompt for another expression while(!checkFloat(input)){ System.out.println("Error in Expression! Cannot accept " + "floating numbers \n"); SimpleIO.prompt("Enter an infix expression to evaluate: \n"); input = SimpleIO.readLine(); } //if user enters incorrect formatted infix show error message and prompt for another expression while(!checkInfix(input)){ System.out.println("Error in Expression! No operator between " + "operands. Also last token must be an operand \n"); SimpleIO.prompt("Enter an infix expression to evaluate: \n"); input = SimpleIO.readLine(); } //if user enters too many operators show error message and prompt for another expression while(!checkOps(input)){ System.out.println("Error in Expression! Operator cannot " + "be preceded by an operator \n"); SimpleIO.prompt("Enter an infix expression to evaluate: \n"); input = SimpleIO.readLine(); } //takes a value for x and creates new infix with entered value char[] c=input.toCharArray(); String input2=""; for(int i=0;i<c.length;i++){ if(c[i]=='x'){ SimpleIO.prompt("Enter a value for x: "); c[i]=SimpleIO.readLine().charAt(0); for(int j=0;j<c.length;j++){ input2+=c[j]; } if(!Character.isDigit(c[i])){ System.out.println("You did not enter an integer " + "value for x "); System.exit(-1); } } } String output; Main theTrans = new Main(input2); output = theTrans.convert(); int result= calculate(output); System.out.println("Postfix is: " + output ); System.out.println("Postfix evaluated is: " + result +'\n'); SimpleIO.prompt("Evaluate another expression? (y/n)"); if (SimpleIO.readLine().equals("n")){ System.exit(0); } } } //class to build stack which host integers and char class integerStack { private char[] stackArray; private int top; public integerStack(int size) { stackArray = new char[size]; top = -1; } public void push(char j) { stackArray[++top] = j; } public char pop() { return stackArray[top--]; } public char peek() { return stackArray[top]; } public boolean isEmpty() { return (top == -1); } } }