我的任务：您的程序应验证输入的电子邮件地址是否包含@符号。如果没有，您的程序应通知用户该电子邮件地址无效。然后程序应该在打印“Goodbye！”消息后退出程序。
提示：如果输入的电子邮件不正确，请考虑使用分支语句（如果/ else）来处理继续程序或退出程序。
提示：考虑使用属于String类的indexOf（）方法来确定包含@符号的电子邮件地址。
我不知道该怎么做;电子邮件地址是由用户的输入声明的，因此它要求您使用此输入声明变量用户名，但@符号前面的所有字符（[email protected] - 希望您将juliariccio打印为用户名）。
**此外，试图弄清楚如何修复此错误，不断弹出所有分支语句：
case "1": System.out.println("\nClassification: Freshman");
^
required: char
found: String
My code for the program is below:
````````//import Scanner documentation
import java.util.Scanner;
public class Riccio_Lesson6 {
public static void main (String [ ] args) {
//declare variables
String fname, lname;
String emailAddress;
int atSign;
//create a scanner object
Scanner keyboard = new Scanner (System.in);
//prompt user for first and last name
System.out.print("Please enter your first and last name: ");
//read user's first name
fname = keyboard.next();
//read user's last name
lname = keyboard.next();
//prompt user for their email address
System.out.print("\nPlease enter your email address: ");
//read user's input
emailAddress = keyboard.next();
//prompt user for their major & classification code
System.out.print("Pleast enter two characters (Character #1: Major Code and Character #2: Classification Code): ");
//read user's input
String input = keyboard.next();
char major = input.charAt(0);
char classification = input.charAt(1);
//print banner to screen
System.out.print("\n*******************************************************************************************************");
System.out.print("\n " + fname.toUpperCase() );
System.out.print(", please review your profile below and learn more about your major.");
System.out.print("\n*******************************************************************************************************");
//create username
atSign = emailAddress.lastIndexOf("@");
username = emailAddress.substring(atSign);
//print outputs to screen
System.out.print("\n\nFirst Name: " + fname);
System.out.print("\nLast Name: " + lname);
System.out.print("\n\nUsername: " + username);
System.out.print("\nEmail Address: " + emailAddress);
//use a switch statement to determine the user's classification
switch (classification){
case "1": System.out.println("\nClassification: Freshman");
break;
case "2": System.out.println("\nClassification: Sophomore");
break;
case "3": System.out.println("\nClassification: Junior");
break;
case "4": System.out.println("\nClassification: Senior");
break;
case "5": System.out.println("\nClassification: Graduate");
break;
default: System.out.println("\nYou've entered an invalid year code!");
}
//use a switch statement to determine the user's major
switch (major){
case "A": System.out.println("\nMajor: Accounting");
System.out.println("\nMajor Description: Accounting supplies quantitative information essential to management decision-making and control, as well as a wide variety of tax and consulting services and information on management's effective use of an organization's resources. This major helps prepare students for careers in public, industrial, or governmental accounting and also provides an appropriate background for those planning to enter law school or graduate school. Public accounting is carried on by independent practitioners, most of whom are certified public accountants.");
break;
case "B": System.out.println("\nMajor: Biology");
System.out.println("\nMajor Description: Biology examines the fundamental concepts of nature and all aspects of the living environment, from the molecular level to the biosphere. Biology can open doors to many specialized fields, including genetics, biotechnology, environmental biology, and medicine. A Biology major can prepare students for further study in graduate or professional schools, and also trains students for careers in industry, education, or government.");
break;
case "C": System.out.println("\nMajor: Computer Science");
System.out.println("\nMajor Description: Computer Science is primarily concerned with the analysis, design, and applications of computing software and systems. It includes programming languages, data structures, compilers, operating systems, data bases, and artificial intelligence.");
break;
case "E": System.out.println("\nMajor: Economics");
System.out.println("\nMajor Description: Economics' studies how individuals make choices in the face of scarcity. Whether dealing with how households determine what goods they buy, why firms produce certain quantities of goods and services, and what forces shape the aggregate performance of economic institutions. Economics is valuable not only for the topic it treats, but also for its rigorous methods of analysis. Economic majors often attend graduate school, law school or business school. Majors who choose to work immediately upon graduation may find employment in financial institutions, manufacturing corporations, consulting firms, and state and federal agencies.");
break;
case "H": System.out.println("\nMajor: History");
System.out.println("\nMajor Description: History examines the human experience from its origins to the present. The history of countries such as Europe, Canada, America, China, Japan, India, Africa, or Latin America may be studied. Focus may be placed on public events of political, diplomatic, and constitutional history, or on the examination the social, cultural, or economic history of subjects such as villages, cities, witchcraft, sex, literacy, and work. History majors may go on to graduate school, law school or business school. Some may go into the work force, finding jobs with multinational corporations, governmental agencies, or small businesses.");
break;
case "I": System.out.println("\nMajor: Information Sciences and Technology");
System.out.println("\nMajor Description: This major is structured to provide students with the theoretical frameworks and skill sets necessary to compete and be productive in the information technology -intensive global context that defines the new Information Age. Specifically, the degree will be focused on a program that will build an understanding of core information technologies and related areas of study; will prepare students for the practical application of various information sciences and related technologies; and engage students in sharpening their abilities to think critically and to work in teams.");
break;
case "J": System.out.println("\nMajor: Journalism");
System.out.println("\nMajor Description: Careers include newspaper reporting and editing, magazine writing, broadcast news, corporate public relations, and advertising account services. This major is based on knowledge of the social and professional responsibilities of communicators, and basic competence in journalistic skills.");
break;
case "M": System.out.println("\nMajor: Mathematics");
System.out.println("\nMajor Description: Mathematics today is a vibrant and dynamic field, manifesting itself in such familiar things as CAT scans, compact discs, and satellite communication. Accordingly, the mathematics program is broad and varied, with studies in calculus, finite, actuarial sciences and algebra. After graduating, majors successfully pursue a variety of careers, working in industry, insurance (as actuaries), government, finance, and other fields. Many graduates may attend professional schools in law, medicine, or business. Others may go directly into teaching; and still others may go on to graduate programs in mathematics, applied mathematics, engineering, economics, and computer science.");
break;
case "P": System.out.println("\nMajor: Physics");
System.out.println("\nMajor Description: Physics studies the fundamental properties and interactions of all forms of matter. Experimental and theoretical investigations are combined to formulate mathematical relationships that describe and predict the behavior of nature. The physics undergraduate program can prepare students for employment in an industrial or governmental laboratory. The program can also prepare students for further study at graduate or professional schools in physics, engineering, biophysics, medicine, education, law, or business.");
break;
case "T": System.out.println("\nMajor: Telecommunications");
System.out.println("\nMajor Description: The primary goal of this major is to prepare students for administrative careers in the electronic media. Its professional emphasis is on management and public policy in telecommunications. Telecommunications may provide course work for students interested in television production, from the perspective of production management and administration. The major also serves students seeking greater understanding of the social role and social control of the broadcasting and cable industries. Telecommunications is especially designed for students considering careers in local cable systems operation, local radio and television station administration, television network and cable MSO operations, corporate video, local and federal public policy positions, and emerging media industries.");
break;
default: System.out.println("\nYou've entered an invalid major code!");
}
}//end of main
}//end of CLASS
要使用switch语句（并消除错误），必须使用char值，而不是String类型。例如，而不是：
switch(major){
case "A": //case 1
case "B": //case 2
case "C": //etc.
使用：
switch(major){
case 'A': //case 1
case 'B': //case 2
case 'C': //etc.
要使用indexOf（）检查@符号，您希望它看起来更像这样：
atsign = emailAddress.indexOf('@');
if(atsign >= 0){
username = emailAddress.substring(0, atsign);
}
基本上，indexOf（char c）将返回找到指定char c的第一个索引，如果该char不在String中，则返回-1。 substring（int start，int end）将返回indeces [start，end]中的String。防爆。
String str = "milkandcookies";
String sub = str.substring(0, 4);
//now printing sub will print "milk"
Scanner keyboard = new Scanner(System.in);
String emailAddress = keyboard.next();
String userName = emailAddress.substring(0, emailAddress.indexOf('@'));
System.out.println(userName);
要解决switch case错误，请用单引号替换case值的双引号
case 'A'