我的作业有问题。该程序应首先运行registration()。如果用户未满13岁，则会发出提醒，并应返回registration()。如果用户超过13岁，它将运行displayProfile()并要求确认，如果答案是肯定的，它将通知它是成功的并且程序结束。如果答案为否，则应返回registration()并处理重复。如果答案无效，它应该继续提示有效答复。
问题出在registration()。在程序开始时，它工作正常，但当我输入一个13岁以下的用户并返回到注册时，它会跳过输入部分的姓氏，而是打印出“名字：” 。它是在while循环中，因为我想验证输入是否只是字符和空格。对于注册中的其他字段，一切正常。它只是在下一次运行时提示输入它不起作用的姓氏。算法出了什么问题？
import java.util.Calendar;
import java.util.Scanner;
public class mainExercise{
static Scanner input = new Scanner(System.in);
static String lastName;
static String firstName;
static String email;
static String gender;
static String bday;
static int birthMonth;
static int birthDay;
static int birthYear;
static String confirmation;
static EmailValidator ev = new EmailValidator();
static Calendar cal = Calendar.getInstance();
public static void main(String[] args){
do{
do{
registration();
}while(validateAge(birthMonth, birthDay, birthYear) != 1);
displayProfile();
do{
confirmation = input.nextLine();
}while(confirm(confirmation)== -1);
if(confirm(confirmation)==0){
break;
}
}while(confirm(confirmation)== 1);
System.out.println("Thank you for registering, " + firstName);
}//end of main
static void registration(){
System.out.println("Welcome to Old School Facebook");
System.out.println("To register, please provide the following information");
System.out.print("Last Name: ");
do{
lastName = input.nextLine();
}while(validateName(lastName) != 1);
System.out.print("First Name: ");
do{
firstName = input.nextLine();
}while(validateName(firstName) != 1);
System.out.print("Email: ");
do{
email = input.nextLine();
}while(validateEmail(email) != 1);
System.out.print("Gender: ");
do{
gender = input.nextLine();
}while(validateGender(gender) != 1);
System.out.println("Enter birthdate");
do{
System.out.print("Month: ");
birthMonth = input.nextInt();
}while(validateBirthInput(birthMonth) != 1);
do{
System.out.print("Day: ");
birthDay = input.nextInt();
}while(validateBirthInput(birthDay) != 1);
do{
System.out.print("Year: ");
birthYear = input.nextInt();
}while(validateBirthInput(birthYear) != 1);
}
static int validateName(String s){
int valid = 1;
char name[] = s.toCharArray();
for(int i=0; i<name.length; i++){
if(Character.isLetter(name[i]) || Character.isWhitespace(name[i])){
valid = 1;
}else{
System.out.println("Invalid input");
valid = 0;
break;
}
}
return valid;
}
static int validateEmail(String s){
int valid = 1;
if(ev.validate(s)){
valid = 1;
}else{
System.out.println("Invalid email");
valid = 0;
}
return valid;
}
static int validateGender(String s){
int valid = 1;
if(s.toLowerCase().compareTo("m") == 0 || s.toLowerCase().compareTo("f") == 0){
valid = 1;
}else{
valid = 0;
}
return valid;
}
static int validateBirthInput(int x){
int valid = 1;
int birth;
try{
birth = x;
}catch(Exception e){
System.out.println("Enter numbers 1-12 for month, 1-31 for day, yyyy for year");
valid = 0;
}
return valid;
}
static int validateAge(int bm, int bd, int by){
int valid = 1;
int cm = cal.get(Calendar.MONTH);
int cd = cal.get(Calendar.DAY_OF_MONTH);
int cy = cal.get(Calendar.YEAR);
if((cy-by)<=13){
if(bm>=cm){
if(bd>cd){
valid = 0;
System.out.println("You must be at least 13 years old");
System.out.println();
}
}
}else{
valid = 1;
}
return valid;
}
static int confirm(String s){
int reply;
if(s.toLowerCase().compareTo("yes") == 0){
reply = 1;
}else if(s.toLowerCase().compareTo("no") >0){
reply = 0;
}else{
System.out.println("Invalid input. Type yes or no");
reply = -1;
}
return reply;
}
static void displayProfile(){
System.out.println();
System.out.println("Last Name: " + lastName);
System.out.println("First Name: " + firstName);
System.out.println("Email: " + email);
System.out.println("Gender: " + gender);
System.out.printf("Birthday: %d/%d/%d\n\n", birthMonth, birthDay, birthYear);
System.out.println("(yes or no): ");
}
}
答案 0 :(得分：2)
查看Scanner.nextInt()的javadoc：
将输入的下一个标记扫描为int
现在将其与Scanner.nextLine()的内容进行比较：
使此扫描程序超过当前行并返回跳过的输入。此方法返回当前行的其余部分，不包括末尾的任何行分隔符。该位置设置为下一行的开头。
因此，当您致电nextInt()时，您只能从输入中读取“int”，当您致电nextLine()时，您会一直读到该行的末尾。您的扫描仪正在从System.in读取，这有点奇怪之处在于，在您点击 之后，它不会向扫描仪提供任何数据无论你自己输入哪一行。当您要求日期/月/年时，用户输入一些数字，但在用户点击输入之前没有任何反应，然后您调用nextInt()，它会读取输入的数字。
到目前为止一直很好，除了扫描仪只读取用户键入的数字，而不是新行。因此，当您再次通过registration()方法时，扫描程序中会有一个备用空白行，lastName = input.nextLine();会立即读取该行，假定它有效，然后继续询问名字。
由于这是您的作业，请查看您正在阅读的内容以及用户输入的内容，请记住，在用户点击之前，System.in不会向扫描程序发送任何内容。 / KBD>。您可以查看此Integer method, parseInt(String)，而不是使用nextInt()。
答案 1 :(得分：0)
我改变了你的代码。您也可以根据自己的需要进行更改.. 快乐的编码.. :)
import java.util.Calendar;
import java.util.Scanner;
public class mainExercise{
static Scanner input = new Scanner(System.in);
static String lastName;
static String firstName;
static String email;
static String gender;
static String bday;
static int birthMonth;
static int birthDay;
static int birthYear;
static String confirmation;
//static EmailValidator ev = new EmailValidator();
static Calendar cal = Calendar.getInstance();
public static void main(String[] args){
do{
do{
registration();
}while(validateAge(birthMonth, birthDay, birthYear) != 1);
displayProfile();
// this is coming "Invalid input. Type yes or no" because ist time input.nextLine() return ("") thats why.
do{
confirmation = input.nextLine();
}while(confirm(confirmation)== -1 || confirmation.equals(""));
if(confirm(confirmation)==1){
break;
}
}while(confirm(confirmation)== 1);
System.out.println("Thank you for registering, " + firstName);
}//end of main
static void registration(){
System.out.println("Welcome to Old School Facebook");
System.out.println("To register, please provide the following information");
System.out.print("Last Name: ");
do{
lastName = input.nextLine();
}while(validateName(lastName) != 1);
System.out.print("First Name: ");
do{
firstName = input.nextLine();
}while(validateName(firstName) != 1);
System.out.print("Email: ");
do{
email = input.nextLine();
}while(validateEmail(email) != 1);
System.out.print("Gender: ");
do{
gender = input.nextLine();
}while(validateGender(gender) != 1);
System.out.println("Enter birthdate");
do{
System.out.print("Month: ");
birthMonth = input.nextInt();
}while(validateBirthInput(birthMonth) != 1);
do{
System.out.print("Day: ");
birthDay = input.nextInt();
}while(validateBirthInput(birthDay) != 1);
do{
System.out.print("Year: ");
birthYear = input.nextInt();
}while(validateBirthInput(birthYear) != 1);
}
static int validateName(String s){
int valid = 1;
char name[] = s.toCharArray();
for(int i=0; i<name.length; i++){
if(Character.isLetter(name[i]) || Character.isWhitespace(name[i])){
valid = 1;
}else{
System.out.println("Invalid input");
valid = 0;
break;
}
}
return valid;
}
static int validateEmail(String s){
int valid = 1;
// this is showing error. You have to first initialize ev variable .
if(ev.validate(s)){
valid = 1;
}else{
System.out.println("Invalid email");
valid = 0;
}
return valid;
}
static int validateGender(String s){
int valid = 1;
// you have to check whith 1st char of that string othrewise it always show false
if(s.toLowerCase().substring(0, 1).compareTo("m") == 0 || s.toLowerCase().substring(0, 1).compareTo("f") == 0){
valid = 1;
}else{
valid = 0;
}
return valid;
}
static int validateBirthInput(int x){
int valid = 1;
int birth;
try{
birth = x;
}catch(Exception e){
System.out.println("Enter numbers 1-12 for month, 1-31 for day, yyyy for year");
valid = 0;
}
return valid;
}
static int validateAge(int bm, int bd, int by){
int valid = 1;
int cm = cal.get(Calendar.MONTH);
int cd = cal.get(Calendar.DAY_OF_MONTH);
int cy = cal.get(Calendar.YEAR);
// this should also need to change like following
if ((cy - by) > 13)
{
return valid;
}
else if ((cy - by) == 13)
{
if (bm>cm)
{
return valid;
}
else if (bm==cm && bd>cd ) {
return valid;
}
}
System.out.println("You must be at least 13 years old");
System.out.println();
return 0;
}
static int confirm(String s){
int reply;
if(s.toLowerCase().compareTo("yes") == 0){
reply = 1;
}else if(s.toLowerCase().compareTo("no") >0){
reply = 0;
}else{
System.out.println("Invalid input. Type yes or no");
reply = -1;
}
return reply;
}
static void displayProfile(){
System.out.println();
System.out.println("Last Name: " + lastName);
System.out.println("First Name: " + firstName);
System.out.println("Email: " + email);
System.out.println("Gender: " + gender);
System.out.printf("Birthday: %d/%d/%d\n\n", birthMonth, birthDay, birthYear);
System.out.println("(yes or no): ");
}
}