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atSymbolIndexCorrectatSymbolIndexThe indexOf() method got the index of @. If found (i.e. not -1), then that index was used to indicate the size of the substring preceding the @. So for [email protected], the @ is at index 10, which is the number of letters in AbeLincoln. Thus, substring() starts at index 0 and gets 10 characters, namely "AbeLincoln".PARTICIPATIONACTIVITY3.12.2: String modification methods.str1 is "Main" and str2 is " Street" (note the leading space).1)Use + to combine str1 and str2, so newStr should be "Main Street".newStr = str1+ str2 ;Correct+ str2 + appends str2 to str1 in a new string.2)Use concat to append a period to str2, so str2 should be " Street."str2 = str2.concat(".");Correctconcat(".")The concat method creates new string with "." appended str2.3)Replace "ai" with "our" in str1, so str1 should be "Mourn".str1 = str1.replace("ai", "our");Correctreplace("ai", "our")Creates a new String in which all occurrences of "ai" are replaced with "our".
CHALLENGEACTIVITY3.12.1: Combining strings.Assign secretID with firstName, a space, and lastName. Ex: If firstName is Barry and lastName is Allen, then output is:Barry Allenimport java.util.Scanner;public class