Chapter 10 Exercise 23, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

10.23 (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 MyString2):
public MyString2(String s);
public int compare(String s);
public MyString2 substring(int begin);
public MyString2 toUpperCase();
public char[] toChars();
public static MyString2 valueOf(boolean b);

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_23 {

    public static void main(String[] args) {

        System.out.println(new MyString1("I'm a string.").toChars());
        MyString1 s1 = new MyString1("test123");
        MyString1 s2 = new MyString1("test123");
        System.out.println("s1 = " + s1.toString());
        System.out.println("s2 = " + s2.toString());
        System.out.println("Is s1 equal to s2? " + s1.compare(s2));
        System.out.println("Value of false changed to uppercase = " + (MyString1.valueOf(false).toUpperCase().toString()));
        System.out.println("Value of true = " + (MyString1.valueOf(true).toString() ));

    }
}