Develop Reference

Simple Password Check

Just beginning to learn java and I am trying to code a simple password check that gives you tries if you type the incorrect password. The problem is when I type the incorrect password and followed by the correct password it still says its the wrong password.
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Tell us the Password");
while(true) {
String password = scanner.nextLine();
if (password.equalsIgnoreCase("Happy")) {
System.out.println("Correct password");
break;
}
else {
for (int i =6; i>0;i--) {
System.out.println("Incorrect password ");
System.out.println(+ i + " Trys left");
password= scanner.nextLine();
}
}
System.out.println("No more tries");
System.out.println("Program exits");
break;
}
}
I want the program to check if the password is correct or incorrect.

Once you entered the wrong password, code flow stuck in the for loop and remain there for available iterations, no comparison with entered password is going on there so you need to modify the flow. One way to do so as per your initial code posted is
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Tell us the Password");
int tryCountForFailure = 6;
while (true) {
String password = scanner.nextLine();
if (password.equalsIgnoreCase("Happy")) {
System.out.println("Correct password");
break;
} else {
System.out.println("Incorrect password ");
System.out.println(tryCountForFailure + " Trys left");
tryCountForFailure--;
if (tryCountForFailure == 0) {
System.out.println("No more trys");
System.out.println("Program exits");
break;
}
}
}
scanner.close();
}

In your code, the loop gets stuck in the Else statement. Let's run through the logic.
The program asks for the password and stores it in a password String.
The program check's if that password is right, if it is the program stops and if not it continues to the else statement.
The program uses a for statement to run this block of code 6 times:
System.out.println("Incorrect password ");
System.out.println(+ i + " Trys left");
password = scanner.nextLine();
The problem is even if you enter a correct String for the password field, it never checks if that value is correct. You would be better of refactoring your code so the logic is sound. Let's run through what should happen.
Program defines a variable named count and set's it to 0.
The program uses a while loop to ask if count is less than 6.
The program takes in a password String with a scanner.
The program checks if that password String is equal to the correct password, if yes, it breaks and,
If it does not equal the correct password it adds one to count
Scanner scanner = new Scanner(System.in);
System.out.println("Tell us the Password");
String password = scanner.nextLine();
if (password.equalsIgnoreCase("Happy")) {
System.out.println("Correct password");
break;
} else {
count++
}
}

JAVA scanner causes if statement problems when using bag

I am new to JAVA and have been using IDE, to cut it short whenever I try to check if bag contains a string thats the same as the given input JAVA counts it as FALSE, even if the if statements such as "is input equal to 1" and "is 1 inside the bag" pass as true. here is an excerpt from my code, I would appreciate any help and advice.
//user input
System.out.println("Please enter a string (to exit, enter 'exit'): ");
a=sc.next();
if (a.equals("1")) {System.out.println("adpkgnosıfbgojadnofabsndofgna");}
if (ValidAnswers1.contains("1")) {System.out.println("adpkgnosıfbgojadnofabsndofgna");}
//error detection. after I learn bag it will become if bag contains string s.
if (ValidAnswers1.contains(a)) {correct_input=1;} else {correct_input=0;}
while (correct_input==0)
{
System.out.println("you entered:"+ a+".");
System.out.println("Please enter a valid string (to exit, enter 'exit')");
a = sc.next();
if (ValidAnswers1.contains(a)) {correct_input=1;} else {correct_input=0;}
}
the console prints out both the keymashes and then diverts into the while loop. I have checked to make sure the while loop is correct by testing with fixed variables, but when scanner is used it seems to have an error.

I didn't understand, what you really want, i did the test and a yet is working fine. take a look at the class, maybe is some error in the variables or something
public class Main {
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
String a;
String ValidAnswers1 = "1";
int correct_input = 0;
//user input
System.out.println("Please enter a string (to exit, enter 'exit'): ");
a = sc.next();
if (a.equals("1")) {
System.out.println("adpkgnosıfbgojadnofabsndofgna");
}
if (ValidAnswers1.contains("1")) {
System.out.println("adpkgnosıfbgojadnofabsndofgna");
}
//error detection. after I learn bag it will become if bag contains string s.
if (ValidAnswers1.contains(a)) {
correct_input=1;
} else {
correct_input=0;
}
while (correct_input==0) {
System.out.println("you entered:"+ a+".");
System.out.println("Please enter a valid string (to exit, enter 'exit')");
a = sc.next();
if (ValidAnswers1.contains(a)) {
correct_input=1;
} else {
correct_input=0;
}
}
}
Here is the output:
Please enter a string (to exit, enter 'exit'):
a
adpkgnos?fbgojadnofabsndofgna
you entered:a.
Please enter a valid string (to exit, enter 'exit')
1
------------------------------------------------------------------------
BUILD SUCCESS
------------------------------------------------------------------------

//Create a new Object Scan in the memmory
Scanner scan = new Scanner(System.in);
String input;
String[] validAnswers = new String[]{"1","2","3","exit"};
boolean isCorrect = false;
//The method equalsIgnoreCase means that the text can be in uppercase too;
/*The number between the tags "[]" means the number in the array since arrays
starts with number "0" */
do{
System.out.println("Please enter a string (to exit, enter 'exit'): ");
input = scan.next();
if(input.equalsIgnoreCase(validAnswers[0])){
isCorrect = true;
System.out.println("Number 1");
}else if(input.equalsIgnoreCase(validAnswers[1])){
isCorrect = true;
System.out.println("Number 2");
}else if(input.equalsIgnoreCase(validAnswers[2])){
isCorrect = true;
System.out.println("Number 3");
}else if(input.equalsIgnoreCase(validAnswers[3])){
isCorrect = true;
System.out.println("EXIT!");
//You could use the method System.exit(0) to finish the program;
//If you put "1" in the exit value means that the prgram finished with some error;
//System.exit(0);
}else{
//If the Answers is different from all of the others;
System.out.println("you entered: " + input +".");
System.out.println("Please enter a valid string (to exit, enter 'exit')");
}
}while(isCorrect != true);
//I used the method do{}while because it's the only method that will exacute at least once;
}

(Java) Input validation not working as intended?

I am trying to validate the input that decides whether or not the program does everything again or terminates. While it works enough that Y and N are the only accepted answers, it never does actually hit the catch statement - it only loops until Y or N are entered because of the while loop. I need to fix this so that the exception gets thrown for any other input, but I don't understand what I've done wrong.
public static String validateChoice(Scanner sc, String choice) {
choice = "";
while (!choice.equalsIgnoreCase("Y") && !choice.equalsIgnoreCase("N")) {
try {
System.out.print("Continue? Y/N: ");
choice = sc.nextLine();
} catch (InputMismatchException e) {
System.out.println("Invalid answer. Please answer only Y or N. Lowercase is accepted.");
sc.nextLine();
continue;
}
}
return choice;
}

Because there is no error here, catch statement cannot be reached. InputMismatchException is thrown only when the input type is incorrect. For example, you ask for nextInt() but the input is double. You are using nextLine(), so all input is accepted.

The problem is you are catching InputMismatchException which is never thrown by the code in try.
System.out.print("Continue? Y/N: ");
choice = sc.nextLine();
See this: https://docs.oracle.com/javase/10/docs/api/java/util/Scanner.html#nextLine()
So, to solve your problem, continue if user enters Y otherwise stop looping. It makes more sense to rely on a value to continue and consider everything else as NO.
if(Y){
continue;
} else { //any other value
break;
}
Full code:
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
do {
System.out.println("Do some stuff");
} while (continueCheck(sc));
System.out.println("Completed");
}
public static boolean continueCheck(Scanner sc) {
System.out.print("Continue? Y/N: ");
String choice = sc.nextLine();
return "Y".equalsIgnoreCase(choice.trim());//true only if Y or y is entered
}

Having an incedibly tough time with a loop

I've copied part of the instructions below, and I can code pretty much every part on its own, but getting the control flow together is giving me massive doubts about my ability.
One of my biggest problems is the int gameChanger. Im supposed to immediately verify if it is a integer or not, and loop back if its not. But then Im also supposed to check to see if thebuser ever types "exit". But the input variable for my scanner instance is an integer... So Im stumped. I can use a try catch to check the missmatchexception once the input is being read in, but that doesnt solve the exit issue nor am I able to come up with solid logic to get the try catch to loop back if it indeed isnt an integer. Im thinking a do while loop but I havent gotten it to work.
Instructions:

You can whether the input is a number before attempting to consume it.
int num;
while (true) {
if (scanner.hasNextInt()) {
num = scanner.nextInt();
break;
} else {
// read whatever is there instead.
String line = scanner.nextLine();
if (line.equals("exit"))
System.exit(0);
System.out.println("Please enter a number");
}
}
System.out.println("Number entered " + num);

This gets the job done. Try it out.
import java.util.Scanner;
public class MyCode
{
public static void main(String[] args)
{
String gameInput = ".";
int gameNumber = 0;
boolean inputLoop = true;
Scanner input = new Scanner(System.in);
while(inputLoop == true)
{
try
{
System.out.print("Please enter a valid game number: ");
gameInput = input.next();
if(gameInput.equals("exit"))
{
System.out.println("Program will now end. Goodbye.");
inputLoop = false;
input.close();
}
gameNumber = Integer.parseInt(gameInput);
if(gameNumber >= 20001 && gameNumber <= 21230)
{
System.out.println("You have inputted a valid game number.");
inputLoop = false;
input.close();
}
}
catch(NumberFormatException e)
{
if(!gameInput.equals("exit"))
{
System.err.println("Invalid game number. Please try again.");
}
}
}
}
}

Need help modifying code for input validation and error message

Need some help with my code. I'm trying to modify written code to ask a user for "yes" or "no" in order for the loop to continue. I'm supposed to use a prime read and a while loop to display an error message if the user inputs anything other than "yes" or "no".
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
//declare local variables
String endProgram = "no";
boolean inputValid;
while (endProgram.equals("no")) {
resetVariables();
number = getNumber();
totalScores = getScores(totalScores, number, score, counter);
averageScores = getAverage(totalScores, number, averageScores);
printAverage(averageScores);
do {
System.out.println("Do you want to end the program? Please enter yes or no: ");
input.next();
if (input.hasNext("yes") || input.hasNext("no")) {
endProgram = input.next();
} else {
System.out.println("That is an invalid input!");
}
}
while (!(input.hasNext("yes")) || !(input.hasNext("no")));
}
}

The hasNext method call doesn't take any parameters. Have a look at the docs.
Therefore you should get the value of the input first:
String response = input.next();
And then test the response:
!response.equalsIgnoreCase('yes') || !response.equalsIgnoreCase('no')
You could put this test into a method as you are checking the same thing multiple times.
It may be easier to see the logic of your program by changing endProgram to a boolean. Perhaps even rename it to running;
boolean running = true;
...
while (running) {
...
String response;
boolean validResponse = false;
while (!validResponse) {
System.out.println("Do you want to end the program? Please enter yes or no: ");
response = input.next();
running = isContinueResponse(response);
validResponse = isValidResponse(response);
if (!validResponse) System.out.println("That is an invalid input!");
}
}