String to Integer (atoi)

StringToInteger.java

public class StringToInteger {
    public int myAtoi(String str) {
        int result = 0;
        int multiplier = 1;
        int startIndex = -1;
        int endIndex = -1;
        int index = 0;
        boolean scanNumber = false;
        boolean signAllowed = true;
        boolean spaceAllowed = true;
        while (index < str.length()) {
            char letter = str.charAt(index);
            if(scanNumber) {
                // Mark the end of number
                if(isNumber(letter)) {
                    endIndex = index;
                    index++;
                } else {
                    break;
                }
            } else {
                // Read spaces
                if(isSpace(letter)) {
                    if(spaceAllowed) {
                        index++;
                    } else {
                        break;
                    }
                } else {
                    spaceAllowed = false;
                    // Read signs
                    if(isSign(letter)) {
                        if(signAllowed) {
                            signAllowed = false;
                            if(letter == '-') {
                                multiplier = -1;
                            }
                            index++;
                        } else {
                            break;
                        }
                    } else {
                        if(isNumber(letter)) {
                            // Mark beginning of numbers
                            startIndex = index;
                            endIndex = index;
                            scanNumber = true;
                            index++;
                        } else {
                            break;
                        }
                    }
                }
            }
        }
        
        if(startIndex >=0 && endIndex >=0) {
            result = readNumber(str, startIndex, endIndex, multiplier);
        }
        return result;
    }
    
    private int readNumber(String text, int startIndex, int endIndex, int multiplier) {
        int result = 0;
        int power = endIndex - startIndex;
        int i = startIndex;
        while(i <= endIndex && !isMax(result)) {
            int digit = text.charAt(i)-'0';
            result += multiplier * (digit * (Math.pow(10,power--)));
            i++;
        }
        return result;
    }
    
    private boolean isMax(int number) {
        return (number == Integer.MAX_VALUE || number == Integer.MIN_VALUE);
    }
    
    private boolean isSpace(char character) {
        return (character == ' '); 
    }
    
    private boolean isNumber(char character) {
        return (character >= '0' && character <= '9'); 
    }
    
    private boolean isSign(char character) {
        return (character == '+' || character <= '-'); 
    }
}