Java - Write code to get substring from start offset

Requirements

Write code to get substring from start offset

Demo

//package com.book2s;

public class Main {
    public static void main(String[] argv) {
        String str = "book2s.com";
        int start = 2;
        System.out.println(substring(str, start));
    }/*from ww w.j a va 2 s  .  com*/

    public static String substring(String str, int start) {
        if (str == null)
            return null;
        if (start < 0)
            start = str.length() + start;
        if (start < 0)
            start = 0;
        if (start > str.length())
            return "";
        else
            return str.substring(start);
    }

    public static String substring(String str, int start, int end) {
        if (str == null)
            return null;
        if (end < 0)
            end = str.length() + end;
        if (start < 0)
            start = str.length() + start;
        if (end > str.length())
            end = str.length();
        if (start > end)
            return "";
        if (start < 0)
            start = 0;
        if (end < 0)
            end = 0;
        return str.substring(start, end);
    }
}

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