Determine if a String is an Integer in Java

NumberTester.java

/**
 * Created by Ilya Gazman on 6/29/2017.
 */
public class NumberTester {

    public static final String MIN_VALUE_32 = Integer.MIN_VALUE + "";
    public static final String MAX_VALUE_32 = Integer.MAX_VALUE + "";
    public static final String MIN_VALUE_64 = Long.MIN_VALUE + "";
    public static final String MAX_VALUE_64 = Long.MAX_VALUE + "";

    public static boolean isInteger64(String value) {
        return isInteger(value, MIN_VALUE_64, MAX_VALUE_64);
    }

    public static boolean isInteger32(String value) {
        return isInteger(value, MIN_VALUE_32, MAX_VALUE_32);
    }

    private static boolean isInteger(String value, String minValue, String maxValue) {
        if (value == null) {
            return false;
        }
        int length = value.length();
        if (length == 0) {
            return false;
        }
        int i = 0;
        if (value.charAt(0) == '-') {
            if (length == 1) {
                return false;
            }
            if (length > minValue.length()) {
                return false;
            }
            i = 1;
            maxValue = minValue;
        } else if (length > maxValue.length()) {
            return false;
        }

        for (; i < length; i++) {
            char c = value.charAt(i);
            if (c < '0' || c > '9') {
                return false;
            }
        }
        
        if (length < maxValue.length()) {
            return true;
        }
        if (length > maxValue.length()) {
            return false;
        }
        for (i = 0; i < length; i++) {
            if (value.charAt(i) > maxValue.charAt(i)) {
                return false;
            }
            if (value.charAt(i) < maxValue.charAt(i)) {
                return true;
            }
        }
        return true;
    }
}