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Asking for a username from an array

I need to create a project where only if a specific username is inputted from the given names in the array, they are allowed to continue to the next menu options. How can I change my code to do this? It is just printing Hello John! Do I need a loop?
public class Project1 {
public static void main(String[] args) {
Scanner input = new Scanner (System.in);
System.out.println("please enter your username!");
String[] username = { "John","Lucy", "Amy", "Noah", "Sam"};
List<String> list = Arrays.asList(username);
if (list.contains("John")) {
System.out.println("Hello!" );
}
else if (list.contains("Lucy")) {
System.out.println("Hello!" );
}
else if (list.contains("Amy")) {
System.out.println("Hello!" );
}
else if (list.contains("Noah")) {
System.out.println("Hello" );
}
else if (list.contains("Sam")) {
System.out.println("Hello" );
}
else {
System.out.println("Please enter a valid username.");
}
}
returns:
Welcome, To start, please enter your username!
Hello John!

You effectivly need a loop to ask the user until the name is valid, a do/while loop is a good choice here
Scanner input = new Scanner(System.in);
List<String> allowedUsernames = Arrays.asList("John", "Lucy", "Amy", "Noah", "Sam");
System.out.println("Welcome, To start, please enter your username!");
String name = "";
do {
if (!name.equals("")) {
System.out.println("Please enter a valid username.");
}
name = input.nextLine();
} while (!allowedUsernames.contains(name));
System.out.println("Hello!");
Welcome, To start, please enter your username!
aa
Please enter a valid username.
uu
Please enter a valid username.
dd
Please enter a valid username.
John
Hello!

How to give each student a unique ID after being created by the user on JAVA program

I am working on a school project that basically allows the user to create, edit or view students. Once a student is created, they each get assigned a unique ID like 1, 2, 3, etc. All the functionally of creation, editing and displaying is working but I am stuck on have to give them a unique ID after created. Here is the code I have and in the // commented areas is what I attempted to do but I am not sure if its right. Any ideas will be very appreciated.
import java.util.Scanner;
import java.io.*;
public class MidTermProject {
public static void main(String[] args) throws IOException {
Scanner keyboard = new Scanner(System.in);
System.out.println("Here is the sample of menu choices for Main Menu.");
System.out.println("\nWelcome to University Enrollment" + "\n1. Create Student" + "\n2. Edit Student" + "\n3. Display Student" + "\n0. --- Quit ---");
System.out.println("Please enter a valid choice(1-10, 0 to Quit) :");
int userInput = keyboard.nextInt();
if(userInput == 1) {
CreateStudent();
} else if(userInput == 2) {
EdithStudent();
} else if(userInput == 3) {
DisplayStudent();
} else if(userInput == 0) {
System.out.print("Done");
} else {
System.out.println("Invalid Option, Please try again.");
userInput = keyboard.nextInt();
if(userInput == 1) {
CreateStudent();
} else if(userInput == 2) {
EditStudent();
} else if(userInput == 3) {
DisplayStudent();
} else if(userInput == 0) {
System.out.print("Done");
}
}
}
public static void CreateStudent() throws IOException {
String FullName;
String address;
String city;
String state;
int StudentID;
Scanner keyboard = new Scanner(System.in);
FileOutputStream fstream =
new FileOutputStream("StudentInfo.dat");
DataOutputStream outputFile =
new DataOutputStream(fstream);
System.out.print("\nPlease enter your information bellow.\n" + "\nFull Name: ");
FullName = keyboard.nextLine();
outputFile.writeUTF(FullName);
System.out.print("Address: ");
address = keyboard.nextLine();
outputFile.writeUTF(address);
System.out.print("City: ");
city = keyboard.nextLine();
outputFile.writeUTF(city);
System.out.print("State: ");
state = keyboard.nextLine();
outputFile.writeUTF(state);
//allowed the user to select their own ID number
System.out.print("Please get a Student ID(1-10): ");
//Store the selected number on StudentID
StudentID = keyboard.nextInt();
//The for loop will increment index each time a user is created
for(int index = 0; index == StudentID; index++) {
//The if statement will compare index and StudentID, if equal will ask the user to enter a different number
if(index == StudentID) {
System.out.print("The selected ID has been selected already, Please select a different ID");
StudentID = keyboard.nextInt();
}
}
//write the number in the file
outputFile.writeInt(StudentID);
System.out.print("Successfully Created");
}
public static void EditStudent() throws IOException {
String editName;
String editaddress;
String editCity;
String editState;
Scanner keyboard = new Scanner(System.in);
RandomAccessFile file =
new RandomAccessFile("StudentInfo.dat", "rw");
file.seek(0);
System.out.print("\nPlease enter NEW information bellow.\n" + "\nFull Name: ");
editName = keyboard.nextLine();
file.writeUTF(editName);
System.out.print("Address: ");
editaddress = keyboard.nextLine();
file.writeUTF(editaddress);
System.out.print("City: ");
editCity = keyboard.nextLine();
file.writeUTF(editCity);
System.out.print("State: ");
editState = keyboard.nextLine();
file.writeUTF(editState);
file.close();
System.out.print("Successfully Edited");
}
public static void DisplayStudent() throws IOException {
FileInputStream fstream = new FileInputStream("StudentInfo.dat");
DataInputStream inputFile = new DataInputStream(fstream);
String student;
boolean endOfFile = false;
while(!endOfFile)
{
try
{
student = inputFile.readUTF();
System.out.print(student + " ");
}
catch (EOFException e)
{
endOfFile = true;
}
}
System.out.println("\nDone");
inputFile.close();
}

Firstly, following Java naming conventions makes your code more readable. So use lowercase first when naming a variable: studentId rather than StudentId. Initial-caps is for class names.
In your create student method, your for loop makes no sense.
for(int index = 0; index == StudentID; index++) {
//The if statement will compare index and StudentID, if equal will ask the user to enter a different number
if(index == StudentID) {
System.out.print("The selected ID has been selected already, Please select a different ID");
StudentID = keyboard.nextInt();
}
}
A for loop simply increments the index defined in the first clause, stepping the increment according to the third clause, until the second clause proves true.
So in your code, if the user enters 4, your loop counts 0, 1, 2, 3, 4 «bingo». Now that we reached the user’s specified number, we go on to ask them for another number. And we’re done. But that process is illogical.
That code fails to accomplish your goal of checking for existing students. You need to review all existing students one-by-one. Compare each existing student ID against the desired ID. Only after exhausting the list of all known students should we use the desired ID. If we find a match on an existing student, then we break out of the loop to ask the user for another choice of ID. And we need another outer loop to continue this “ask, search, ask again if needed” process until an unused desired ID is determined.
Big tip: If you write out your problem statement and solution attempt as plain prose, similar to what I just did in the paragraph above, your programming will go more smoothly. And your written prose will be fodder for writing helpful comments in your source code.

Comparing elements of ArrayList in loop gives unexpected result?

The following code checks only the first item in the ArrayList. When I type in an item that is in the ArrayList but not in the first position, I get my error message as "Please enter a valid name".
How can I fix this? Thank you!
Here is my code:
private ArrayList<Account> accounts = new ArrayList<>();
for(Account a : accounts)
{
while(true)
{
System.out.printf("Customer name: ");
String customerName = scanner.next();
if(customerName.equals(a.getName()))
{
System.out.println("You entered " + a.getName());
break;
}
else
{
System.out.println("Please enter a valid name");
}
}
}

You have to break from while. When you iterating on list you have to think about logic. Its can be like this code ;
ArrayList<Account> accounts = new ArrayList<>();
boolean isMatched = false;
while (true) {
for (Account account : accounts) {
System.out.printf("Customer name: ");
String customerName = scanner.next();
if (customerName.equals(account.getName())) {
isMatched = true;
break;
}
}
if (isMatched) {
System.out.println("You entered " + account.getName());
break;
}
System.out.println("Please enter a valid name");
}
PS: boolean value to when found the customer name for ending while loop.

The inner loop does do that:
while(true) {
has no purpose here. It simply keeps looping inside the outer loop, therefore always comparing against the same a account!
Basically you have to swap the two loops!

The problem is the infinite while loop.
while(true)
This loop breaks only when customerName == firstElement.Name, else it is an infinite loop. Instead I think what you want to try is moving the while loop outside the for loop. So the code will look something like this.
private ArrayList<Account> accounts = new ArrayList<>();
while(true)
{
System.out.printf("Customer name: ");
String customerName = scanner.next();
for(Account a : accounts){
if(customerName.equals(a.getName())){
System.out.println("You entered " + a.getName());
break;
}else{
System.out.println("Please enter a valid name");
}
}
}

The problem you have it's because you are only checking the first element all the time. Just after you entering your first element, (and breaking your loop while(1)) you will pass to the second one.
Imagine you have in your arrayList
"hello", "bye"
You'll be inside your loop until texting the first element ("hello").
Solution:
while(true)
{
System.out.printf("Customer name: ");
String customerName = scanner.next();
if (accounts.contains(customerName)){
System.out.println("You entered " + customerName);
break;
}
else{
System.out.println("Please enter a valid name");
}
}

Validating a string scanner

I am creating an "add customer" method and I want to validate the "add forename" scanner so that only a string can be entered and if the user enters an int etc it will throw up an error, below is the code I have got so far.
I have used "Harry" as an example, the concept seems to be working but obviously not every customer is going to be called Harry. Any help would be welcome!
boolean validInput12 = false;
String userOption13 = "";
do {
System.out.println("Enter Customer Forename");
if (sc2.hasNext()) {
userOption13 = sc2.next();
if (userOption13.matches("Harry")) {
validInput12 = true;
sc2.nextLine();
} else {
System.out.println("Input invalid: Please select a valid customer forename");
}
} else {
System.out.print("Input invalid: Please enter a valid name \n");
sc2.nextLine();
}
} while (!validInput12);

Java code not running as planned

This isn't the entire code, just the problem area. (Full code below)
if (passLength > 4) {
System.out.println("Signup alost complete.");
Random rand = new Random();
int randm = rand.nextInt(100000) + 1;
System.out.println(
"To confirm you are not a robot, please enter this code: "
+ randm);
String code = userInput.next();
if (code.equals(randm)) {
System.out.println("Thank you, " + userName);
System.out.println(
"You may now login. Begin by entering your username");
if (userInput.equals(userName)) {
System.out.println("Now please enter you password");
}
// Where the rest of the program will go
}
else {
System.out.println("The code entered is incorrect.");
}
}
else {
System.out.println("Invalid Password");
}
I am making a program where the user makes an account, then later signs in. The part I am having trouble with is a verification to ensure the user is human (they obviously are, but still). After creating their username and password, I generate and print a random int, and they have to type it back.
My problem is that the program always skips to the else statement, and prints "The code entered is incorrect." Even when I enter it perfectly.
Can anyone tell me what I'm doing wrong?
Below is the entire code, just in case.
public static void main(String[] args) {
System.out.println("Hi! To begin please choose your username.");
System.out.println("To do this, please enter your username below. ");
System.out.println("This name must be at least three characters.");
Scanner userInput = new Scanner(System.in);
String userName = userInput.next();
int nameLength = userName.length();
if (nameLength > 2) {
System.out.println("Now please enter your password.");
System.out
.println("This password must be at lease five characters");
String passWord = userInput.next();
int passLength = passWord.length();
if (passLength > 4) {
System.out.println("Signup alost complete.");
Random rand = new Random();
int randm = rand.nextInt(100000) + 1;
System.out.println(
"To confirm you are not a robot, please enter this code: "
+ randm);
String code = userInput.next();
if (code.equals(randm)) {
System.out.println("Thank you, " + userName);
System.out.println(
"You may now login. Begin by entering your username");
if (userInput.equals(userName)) {
System.out.println("Now please enter you password");
}
// Where the rest of the program will go
}
else {
System.out.println("The code entered is incorrect.");
}
}
else {
System.out.println("Invalid Password");
}
}
else {
System.out.println("Invalid Username");
}
}

You are comparing a String with an integer, which can't be the same obviously.
int randm = rand.nextInt(100000) + 1;
...
String code = userInput.next();
if (code.equals(randm))
To solve the problem you could convert the integer to a String and compare the strings (or the other way).
String randm = String.valueOfrand.nextInt(100000) + 1;
...
String code = userInput.next();
if (code.equals(randm)) // Comparing string now
Edit : As #Pshemo pointed out, int code = userInput.nextInt(); will do the work given that you compare the integers with ==.

It's because randm is int and code is String. So the code if (code.equals(randm)) always results to false.

You cannot compare a string and an integer.
Trying taking the input as an integer instead of a String.
String code = userInput.next();
Instead use:
int code= userInput.nextInt();
if(code==randm)
Or you could convert the integer to a String as well