Chapter 10 Exercise 22, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

10.22 (Implement the String class) The String class is provided in the Java library.
Provide your own implementation for the following methods (name the new class MyString1):
public MyString1(char[] chars);
public char charAt(int index);
public int length();
public MyString1 substring(int begin, int end);
public MyString1 toLowerCase();
public boolean equals(MyString1 s);
public static MyString1 valueOf(int i);

import java.util.ArrayList;
public class MyString1 {

    char[] chars;

    public MyString1(char[] chars) {

        this.chars = new char[chars.length];

        for (int i = 0; i < chars.length; i++)
            this.chars[i] = chars[i];


    }

    public MyString1(String string) {
        this(string.toCharArray());
    }

    public char charAt(int index)  {

        return chars[index];

    }

    public int length() {

        return chars.length;
    }

    public MyString1 substring(int begin, int end) {
        char[] s = new char[end - begin];
        for (int i = begin; i < end; i++) {
            s[i - begin ] = chars[i];
        }
        return new MyString1(s);
    }

    public MyString1 toLowerCase() {
        // A = 65
        // a = 97
        char[] lowerCase = new char[chars.length];

        for (int i = 0; i < chars.length; i++) {
            if (chars[i] >= 'A' && chars[i] <= 'Z') {
                lowerCase[i] = (char)(chars[i] + 32);
            } else {
                lowerCase[i] = chars[i];
            }
        }

        return new MyString1(lowerCase);

    }

    public boolean equals(MyString1 s) {

        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) != chars[i]) return false;
        }

        return true;
    }

    public static MyString1 valueOf(int i) {

        int length = getCount(i);
        char[] number = new char[length];
        for (int j = length - 1; j >= 0; j--) {
            number[j] = (char)('0' + (i % 10));
            i /= 10;
        }
        return new MyString1(number);
    }

    public static MyString1 valueOf(long i) {

        int length = getCount(i);
        char[] number = new char[length];
        for (int j = length - 1; j >= 0; j--) {
            number[j] = (char)('0' + (i % 10));
            i /= 10;
        }
        return new MyString1(number);
    }

    private static int getCount(long i) {
        int length = 0;
        while (i > 0) {
            i /= 10;
            length++;
        }
        return length;
    }

    public int compare(String s) {

        int limit = Math.min(s.length(), length());

        char[] chArray = s.toCharArray();
        int i = 0;
        while (i < limit) {
            char ch1 = charAt(i);
            char ch2 = chArray[i];
            if (ch1 != ch2) {
                return ch1 - ch2;
            }
            i++;
        }

        return length() - s.length();

    }

    public int compare(MyString1 s) {

        return compare(new String(s.toChars()));

    }
    public MyString1 substring(int begin) {
        return substring(begin, chars.length);
    }
    public MyString1 toUpperCase() {

        char[] temp = new char[chars.length];
        for (int i = 0; i < chars.length; i++) {
            if (chars[i] >= 'a' && chars[i] <='z') {
                temp[i] = (char)(chars[i] - 32);
            } else {
                temp[i] = chars[i];
            }
        }

        return new MyString1(temp);
    }
    public char[] toChars() {
        return chars;
    }

    @Override
    public String toString() {
        return new String(chars);
    }

    public static MyString1 valueOf(boolean b) {
        return new MyString1((b) ? "true" : "false");
    }

    //  split("ab#12#453", "#") returns ab, #, 12, #, 453
    public static String[] split(String s, String regex) {

        if (isRegexArray(regex)) {
            return arraySplit(s, regex);
        } else {
            return wordSplit(s, regex);
        }

    }

    private static String[] wordSplit(String s, String regex) {

        ArrayList<String> temp = new ArrayList<>();

        int newIndex = 0;
        for (int i = 0; i < s.length() - regex.length(); i++) {

            if (regex.compareTo(s.substring(i, i + regex.length() )) == 0) {
                temp.add(s.substring(newIndex, i));
                temp.add(regex);
                newIndex = i + regex.length();
            }

        }
        temp.add(s.substring(newIndex, s.length()));
        return temp.toArray(new String[temp.size()]);
    }

    private static String[] arraySplit(String s, String regex) {
        char[] regexChars = getRegex(regex);

        ArrayList<String> temp = new ArrayList<>();
        int newIndex = 0;
        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            for (int j = 0; j < regexChars.length; j++) {

                if (ch == regexChars[j]) {
                    if (newIndex != i)
                        temp.add(s.substring(newIndex, i));
                    temp.add("" + regexChars[j]);
                    newIndex = i + 1;
                }
            }
        }
        temp.add(s.substring(newIndex, s.length()));
        return temp.toArray(new String[temp.size()]);
    }

    private static char[] getRegex(String regex) {

        if (regex.charAt(0) != '[' && regex.charAt(regex.length() - 1) != ']')
            return regex.toCharArray();
        else
            return regex.substring(1, regex.length() - 1).toCharArray();

    }

    private static boolean isRegexArray(String regex) {
        return (regex.charAt(0) == '[' && regex.charAt(regex.length() - 1) == ']');
    }

}

public class Exercise_22 {

    public static void main(String[] args) {
        // MyString1
        MyString1 num = MyString1.valueOf(987654321L);
        System.out.println(num.toChars());
        MyString1 s = new MyString1("Test123");
        System.out.println(s.length());
        System.out.println(s.charAt(1));
        System.out.println(s.equals(new MyString1("Test123")));
        System.out.print(MyString1.valueOf(345).toChars());
    }
}