Thread: if else statement not working properly

help me in this code?
my if else statement was not working properly?
it always show valid?
even the user put an invalid expression?
what was i need to do? to solve it
thanks in advance..

import java.io.IOException;
import java.io.*;
import java.util.Arrays;
 
public class datastruct {
 
 
  public static void main(String[] args) throws IOException {
 
 
  	BufferedReader A = new BufferedReader (new InputStreamReader(System.in));
  	String mathex;
  	String output = "";  
  	String out;
  	System.out.println("Enter a Mathematical Expresion:" );
	mathex = A.readLine();
 
 
    int countOperators = 0;
    int countOperands = 0;
 
 
  for(int i = 0; i < mathex.length(); i++) {
     char ch = mathex.charAt(i);
     out = A.readLine();
 
 
     	 if(ch == '+' || ch == '-' || ch == '*' || ch == '/' || ch == '%') {
       countOperators++;
 
 
     	if ( (out.equals("num"))){
 
		System.out.println("invalid");
	}
	else if ( (out.equals("(")) || (out.equals("ch"))){	
 
		System.out.println("valid");
	}
	else if ( (out.equals(")")) || (out.equals("ch"))){	
 
		System.out.println("invalid");
	}
	else if ((out.equals ("(")) || (out.equals  ("ch"))){
 
		System.out.println("valid");
	}
	else {
 
		System.out.println("valid");
	}
 
 
 
    System.out.println("INFIX is: " + mathex );
    System.out.println("POSTFIX is: " + mathex );
    System.exit(0);
 
     } 
     else
     countOperands++;
     }
 
    if((countOperators + 1) != countOperands || mathex.length() == 1){
      System.out.println("INVALID MATHEMATICAL EXPRESSION!!!!!"+ '\n');
    }
 
  	}
  }