[SyferZookie]

import java.io.*;
import java.util.*;
public class Mlab2
{
// initialize two stacks: operator and operand
private static Stack operatorStack = new Stack();
private static Stack operandStack = new Stack();
// method converts infix expression to postfix notation
private static String toPostfix(String infix)
{
StringTokenizer s = new StringTokenizer(infix);
// divides the input into tokens for input
String symbol, postfix = "";
while (s.hasMoreTokens())
// while there is input to be read
{
symbol = s.nextToken();
// if it's a number, add it to the string
if (Character.isDigit(symbol.charAt(0)))
postfix = postfix + " " + (Integer.parseInt(symbol));
else if (symbol.equals("("))
// push "("
{
Character operator = new Character('(');
operatorStack.push(operator);
}
else if (symbol.equals(")"))
// push everything back to "("
{
while (((Character)operatorStack.peek()).charValue() != '(')
{
postfix = postfix + " " + operatorStack.pop();
}
operatorStack.pop();
}
else
// print operatorStack occurring before it that have greater precedence
{
while (!operatorStack.empty() && !(operatorStack.peek()).equals("(") && prec(symbol.charAt(0)) <= prec(((Character)operatorStack.peek()).charValue()))
postfix = postfix + " " + operatorStack.pop();
Character operator = new Character(symbol.charAt(0));
operatorStack.push(operator);
}
}
while (!operatorStack.empty())
postfix = postfix + " " + operatorStack.pop();
return postfix;
}
// method evaulates postfix expression
private static int evaluate(String postfix)
{
StringTokenizer s = new StringTokenizer(postfix);
// divides the input into tokens for input
int value;
String symbol;
while (s.hasMoreTokens())
{
symbol = s.nextToken();
if (Character.isDigit(symbol.charAt(0)))
// if it's a number, push it onto stack
{
Integer operand = new Integer(Integer.parseInt(symbol));
operandStack.push(operand);
}
else // if it's an operator, operate on the previous two popped operandStack items
{
int op2 = ((Integer)operandStack.pop()).intValue();
int op1 = ((Integer)operandStack.pop()).intValue();
int result = 0;
switch(symbol.charAt(0)){
case '*': {
 result = op1 * op2; break;
 }
case '+': {
 result = op1 + op2; break;
 }
case '-': {
 result = op1 - op2; break;
 }
case '/': {
 result = op1 / op2; break;
 }
case '%': {
 result = op1 % op2; break;
 }
case '^': {
 result = op1 ^ op2; break;
 }
}
Integer operand = new Integer(result);
operandStack.push(operand);
}
}
value = ((Integer)operandStack.pop()).intValue();
return value;
}
// method compares operators to establish precedence
private static int prec(char x){
if (x == '+' || x == '-'){
return 1;
}
else if (x=='^' && x == '*' || x == '/' || x == '%'){
return 2;
}
else{
return 0;
}
}

public static void main(String args[]) throws IOException{
String infix;
BufferedReader keyboard = new BufferedReader (new InputStreamReader(System.in));

System.out.print("Input a infix: ");
infix = keyboard.readLine();

System.out.println("Expression in postfix:" + toPostfix(infix));

System.out.println("Evaluated expression: " + evaluate(toPostfix(infix)));
}
}

error occured

Input a infix: 1+1
Exception in thread "main" java.lang.NumberFormatException: For input string: "1
+1"
        at java.lang.NumberFormatException.forInputString(NumberFormatException.
java:48)
        at java.lang.Integer.parseInt(Integer.java:456)
        at java.lang.Integer.parseInt(Integer.java:497)
        at Mlab2.toPostfix(Mlab2.java:23)
        at Mlab2.main(Mlab2.java:125)

before that it has a warning when i build it.

Note: D:\syfer\Mlab2.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
Process completed.

and 1 more think
i also need a help about my
infix to prefix

[SyferZookie]

import java.io.*;
import java.util.*;
public class Mlab2{
private static Stack operatorStack = new Stack ();
private static Stack operandStack = new Stack ();

private static String toPostfix(String infix){
StringTokenizer s = new StringTokenizer(infix);
String symbol, postfix = "";
while (s.hasMoreTokens()){
symbol = s.nextToken();
if (Character.isDigit(symbol.charAt(0))){
postfix = postfix + " " + (Integer.parseInt(symbol));
}else if (symbol.equals("(")){
Character operator = new Character('(');
operatorStack.push(operator);
}else if (symbol.equals(")")){
while (((Character)operatorStack.peek()).charValue() != '('){
postfix = postfix + " " + operatorStack.pop();
}
operatorStack.pop();
}else{
while (!operatorStack.empty() && !(operatorStack.peek()).equals("(") && prec(symbol.charAt(0)) <= prec(((Character)operatorStack.peek()).charValue()))
postfix = postfix + " " + operatorStack.pop();
Character operator = new Character(symbol.charAt(0));
operatorStack.push(operator);
}}
while (!operatorStack.empty())
postfix = postfix + " " + operatorStack.pop();
return postfix;
}
private static String toPrefix(String infix){
 StringTokenizer pre = new StringTokenizer(infix);
 
 String symbol1 , prefix= "";
 while(pre.hasMoreTokens()){
  symbol1 = pre.nextToken();
  
  if(Character.isDigit(symbol1.charAt(0))){
   prefix = prefix+ " " +(Integer.parseInt(symbol1));
   }else if(symbol1.equals("(")){
    Character operand = new Character('(');
    operandStack.push(operand);
    }else if(symbol1.equals(")")){
     while (((Character)operandStack.peek()).charValue()!= '('){
      prefix = prefix + " " + operandStack.pop();
     }
     operandStack.pop();
    }else{
     while(!operandStack.empty()&&!(operandStack.peek()).equals("(")
     && prec(symbol1.charAt(0))<= prec(((Character)operandStack.peek()).charValue()))
     
     prefix = prefix + " "+ operandStack.pop();
     Character operand = new Character(symbol1.charAt(0));
     operandStack.push(operand);
    }}
    while(!operandStack.empty())
    prefix = prefix + " " +operandStack.pop();
    return prefix;
   }
 
private static int evaluate(String postfix){
StringTokenizer s = new StringTokenizer(postfix);
int value;
String symbol;
while (s.hasMoreTokens()){
symbol = s.nextToken();
if (Character.isDigit(symbol.charAt(0))){
Integer operand = new Integer(Integer.parseInt(symbol));
operandStack.push(operand);
}else {
int op2 = ((Integer)operandStack.pop()).intValue();
int op1 = ((Integer)operandStack.pop()).intValue();
int result = 0;
switch(symbol.charAt(0)){
case '*': {
 result = op1 * op2; break;
 }
case '+': {
 result = op1 + op2; break;
 }
case '-': {
 result = op1 - op2; break;
 }
case '/': {
 result = op1 / op2; break;
 }
case '%': {
 result = op1 % op2; break;
 }
case '^': {
 result = op1 ^ op2; break;
 }
}
Integer operand = new Integer(result);
operandStack.push(operand);
}
}
value = ((Integer)operandStack.pop()).intValue();
return value;
}
private static int prec(char x){
if (x == '+' || x == '-'){
return 1;
}
else if (x=='^' && x == '*' || x == '/' || x == '%'){
return 2;
}
else{
return 0;
}
}
public static void main(String args[]) throws IOException{
BufferedReader keyboard = new BufferedReader (new InputStreamReader(System.in));
String infix;
System.out.print("Input a infix: ");
infix = keyboard.readLine();
System.out.println("Expression in postfix:" + toPostfix(infix));
System.out.println("Expression in prefix: " + toPrefix(infix));
 
}
}

code has been edited to this
but my problem now is
the answer im looking for is not appearing like

i input'd
a infix : a+b
the answers are:

POSTFIX: a
PREFIX: a
which are not the real answer.

kindly please help me out