infix to postfix (existing only +, -, *, / ) need to add one more condition(to the power of " ^ ") into this coding

Question

public static boolean operator(String s)
{
if(s.equals("+"))
return true;
else if(s.equals("-"))
return true;
else if(s.equals("*"))
return true;
else if(s.equals("/"))
return true;
else
return false;
}

public static boolean precedence(String s1,String s2)
{
int precedence1 = 0;
int precedence2 = 0;

if(s1.equals("+") || s1.equals("-"))
{
precedence1 = 1;
}
else if(s1.equals("*") || s1.equals("/"))
{
precedence1 = 2;
}

if(s2.equals("+") || s2.equals("-"))
{
precedence2 = 1;
}
else if(s2.equals("*") || s2.equals("/"))
{
precedence2 = 2;
}

if(precedence1 > precedence2 || precedence1 == precedence2)
{
return true;
}
else
return false;
}

public static int evaluatePostFix(String string)
{
Stack<Integer> stack = new Stack<Integer>();
int value = 0;
String[] s = string.split(" ");

for(int i = 0 ; i<s.length;i++)
{
if(!operator(s[i]) && !s[i].isEmpty())
{
stack.push(Integer.parseInt(s[i]));
}
else if(operator(s[i]))
{
int op1 = stack.pop();
int op2 = stack.pop();
int value2 = 0;

switch(s[i])
{
case "+":
value2 = op1 + op2;
break;

case "-":
value2 = op2 - op1;
break;

case "*":
value2 = op1 * op2;
break;

case "/":

Answer 1

u gave not much explanation :/