将字符串分成两半

我正在制作一个新的转换软件来隐藏消息(以娱乐为目的).我做了一个二进制和十进制转换类，我的想法是，用户输入一个字符串，它将全部转换为二进制格式.然后将其分成两半，将一半转换为十进制，然后再次将字符串加在一起，以使其成为二进制和十进制的混合.在其他版本中，我将添加更多的转换，更多的拆分，并且也许也转换为语言.我需要将字符串分成两半.到目前为止，这是我的代码:

I am making a new conversion software to hide messages (for fun). I have made a Binary and Decimal conversion class and my idea is, a user inputs string, it converts all to Binary format. Then splits it in half, converts one half to decimal, then adds the string back together again to make it a mix of binary and decimal. In other versions I will add more conversions, more splits,and maybe convert to languages too. I need splitting the string in half. This is my code so far::

public ray() {
    Scanner in = new Scanner(System.in);

    while (true) {
        System.out.println("Please input the text you wish to encode!");
        System.out.println("Type '#' to quit the Software.");
        String s1 = in.nextLine();
        if ("#".equalsIgnoreCase(s1)) {
            System.out.println("Goodbye, hope you enjoyed RAYConversion v1.0 Alpha.");
            // close software
        }

        // convert all to binary
        binary Binary = new binary();

        //what i need to do is split stirng s1 in half, make it into different strings. Then I will convert
        //the two strings to binary and decimal. I made a converter for that.

    }
}