Write a Java method toDecimalString() that receives a string with hexadecimal symbols and returns another string where every hexadecimal symbol is converted individually to its decimal representation. If the received string contains a wrong hexadecimal value, it should return an error message. To test your method, write a main() method that enables the user to input a string in hexadecimal format, removes eventual extra spaces from it, and makes all characters of the string in upper case. Then, sends this string to toDecimalString() and displays the returned string (decimal format or error message).

Implement a new concat method in the String class you worked on for HW2.  The method should return a new String object that represents the text you would end up with if the argument String were "added onto the end of" this String.  For example, in the code below, the String object answer should represent the text "bookstore" and true should be printed the screen. char[] bookA = {'b', 'o', 'o', 'k'}; char[] storeA = {'s', 't', 'o', 'r', 'e'}; char[] bookstoreA = {'b', 'o', 'o', 'k', 's', 't', 'o', 'r', 'e'}; String book = new String(bookA); String store = new String(storeA); String bookstore = new String(bookstoreA); String answer = book.concat(store); System.out.println(answer.equals(bookstore));     In the text area below, type in your definition of the concat method.  (In other words, type in the code that should replace the //TODO comment.)  Your code cannot call any methods.   public class String {     private char[] data;       public String(char[] value) {         data = new…

Write a Java program that use the String methods indexOf and substring to find the first word in a string. We define word to be a string of characters that does not include whitespace. For example, the first word of the string " Hello, my good friend!" is the string "Hello," and the second word is the string "my". Your program should prompt the user to enter a sentence from the keyboard and then display the first word. A possible dialogue with the user might be:   Enter a sentence: Hello, my good friend! The first word in your sentence is: Hello,

Write a method myConcat that takes a string of multiple words and it returns a string made up of all the words concatenated together with the whitespace removed.