java字符串截取指定下标位置的字符串

public class A {
    public static void main(String[] args) {
        //定义的字符串
        String s = "Hello World";
//        通过length方法获取字符串长度
        for (int i = 0;i < s.length();i++){
            //charAt是获取字符串第i个字符
            System.out.println(s.charAt(i));
        }

        String a = s.replaceAll(s.substring(7,s.length()),"");
        System.out.println(a);

        System.out.println(s.substring(2,7));
    }
}