Chapter 10 Exercise 27, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

10.27 (Implement the StringBuilder class) The StringBuilder class is provided
in the Java library. Provide your own implementation for the following methods
(name the new class MyStringBuilder1):
public MyStringBuilder1(String s);
public MyStringBuilder1 append(MyStringBuilder1 s);
public MyStringBuilder1 append(int i);
public int length();
public char charAt(int index);
public MyStringBuilder1 toLowerCase();
public MyStringBuilder1 substring(int begin, int end);
public String toString();

public class MyStringBuilder1 {

    private char[] buffer;
    public MyStringBuilder1(char[] chars) {
        buffer = new char[chars.length];

        System.arraycopy(chars, 0, buffer, 0, chars.length);
    }

    public MyStringBuilder1(String s) {
        this(s.toCharArray());
    }

    public MyStringBuilder1 append(int i) {

        String temp = "";
        while (i > 0) {
            temp = i % 10 + temp;
            i /= 10;
        }
        return new MyStringBuilder1(toString() + temp);
    }

    public MyStringBuilder1 append(MyStringBuilder1 s) {

        return new MyStringBuilder1(toString() + s.toString());
    }

    public String toString() {
        return new String(buffer);
    }

    public int length() {
        return buffer.length;
    }

    public char charAt(int i) {
        return buffer[i];
    }

    public MyStringBuilder1 toLowerCase() {
        char[] lower = new char[buffer.length];

        for (int i = 0; i < buffer.length; i++) {
            char old = buffer[i];
            if (old >= 'A' && old <= 'Z') {
                lower[i] = (char) (old - 'A' + 'a');
            } else {
                lower[i] = old;
            }
        }
        return new MyStringBuilder1(lower);
    }

    public MyStringBuilder1 substring(int begin, int end) {

        char[] temp = new char[end - begin];
        for (int i = begin; i < end; i++) {
            temp[i - begin] = buffer[i];
        }

        return new MyStringBuilder1(temp);
    }

    public MyStringBuilder1 insert(int offset, MyStringBuilder1 s) {
        char[] temp = new char[s.length() + buffer.length];
        for (int i = 0; i < offset; i++) {
            temp[i] = buffer[i];
        }

        for (int i = 0; i < s.length(); i++) {
            temp[offset + i] = s.charAt(i);

        }
        for (int i = offset + s.length(); i < temp.length; i++) {
            temp[i] = buffer[offset++];
        }

        return new MyStringBuilder1(temp);
    }

    public MyStringBuilder1 reverse() {
        char[] reverse = new char[buffer.length];

        int start = 0;
        for (int i = buffer.length - 1; i >= 0; i--) {
            reverse[i] = buffer[start++];
        }
        return new MyStringBuilder1(reverse);
    }

    public MyStringBuilder1 substring(int begin) {
        return substring(begin, buffer.length);
    }

    public MyStringBuilder1 toUpperCase() {

        char[] temp = new char[buffer.length];

        for (int i = 0; i < buffer.length; i++) {
            char ch = buffer[i];
            if (ch >= 'a' && ch <= 'z') {
                temp[i] = (char) (ch - 'a' + 'A');
            } else {
                temp[i] = ch;
            }
        }
        return new MyStringBuilder1(temp);
    }



}

public class Exercise_27 {

    public static void main(String[] args) {

        MyStringBuilder1 s = new MyStringBuilder1("ButtonDemo");
        System.out.println(s.toString());
        System.out.println(s.append(100).toString());
        System.out.println(s.toString());
        System.out.println("lowercase = " + s.toLowerCase());
        System.out.println("substring 0 3: " + s.substring(0, 3));

    }
}