How to implement Integer.parseInt() method ?

The method must produce :

• 12345 for "12345"
• -12345 for "-12345"
• Error for Alphanumeric input string

Algorithm

int i = 0, number = 0;

char[] value = inputStr.toCharArray();

// Check for -ve number, and set the flag

boolean isNegative = false;

if (value[0] == '-') {

    isNegative = true;

    i = 1;

}

// iterate each character 

while(i < value.length) {

    // Pick each character

    char ch = value[i++];

    int place_value = ch - '0';

    // Check for digit and form the number

    if (place_value>=0 && place_value<=9) {

       number *= 10;

       number += (ch - '0');

    } else {

       System.out.println("Wrong input format!!");

         throw new ParseException("String to int parse",-1);

     }

}

// For -ve number, Negate the number

if(isNegative) {

     number = -number;

}

return number;