Develop Reference

Stuck in Infinite loop, why it does not wait for scanner to re-enter the values [duplicate]

my question is short and sweet. I do not understand why my program infinitely loops when catching an error. I made a fresh try-catch statement but it looped and even copied, pasted and modified the appropriate variables from a previous program that worked. Below is the statement itself and below that will be the entire program. Thank you for your help!
try {
input = keyboard.nextInt();
}
catch(Exception e) {
System.out.println("Error: invalid input");
again = true;
}
if (input >0 && input <=10)
again = false;
}
Program:
public class Blanco {
public static int input;
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here
nameInput();
}
/**
*
* #param name
*/
public static void nameInput() {
System.out.println("What is the name of the cartoon character : ");
Scanner keyboard = new Scanner(System.in);
CartoonStar star = new CartoonStar();
String name = keyboard.next();
star.setName(name);
typeInput(keyboard, star);
}
public static void typeInput(Scanner keyboard, CartoonStar star) {
boolean again = true;
while(again){
System.out.println("What is the cartoon character type: 1 = FOX,2 = CHICKEN,3 = RABBIT,4 = MOUSE,5 = DOG,\n"
+ "6 = CAT,7 = BIRD,8 = FISH,9 = DUCK,10 = RAT");
try {
input = keyboard.nextInt();
}
catch(Exception e) {
System.out.println("Error: invalid input");
again = true;
}
if (input >0 && input <=10)
again = false;
}
switch (input) {
case 1:
star.setType(CartoonType.FOX);
break;
case 2:
star.setType(CartoonType.CHICKEN);
break;
case 3:
star.setType(CartoonType.RABBIT);
break;
case 4:
star.setType(CartoonType.MOUSE);
break;
case 5:
star.setType(CartoonType.DOG);
break;
case 6:
star.setType(CartoonType.CAT);
break;
case 7:
star.setType(CartoonType.BIRD);
break;
case 8:
star.setType(CartoonType.FISH);
break;
case 9:
star.setType(CartoonType.DUCK);
break;
case 10:
star.setType(CartoonType.RAT);
break;
}
popularityNumber(keyboard, star);
}
public static void popularityNumber(Scanner keyboard, CartoonStar star) {
System.out.println("What is the cartoon popularity number?");
int popularity = keyboard.nextInt();
star.setPopularityIndex(popularity);
System.out.println(star.getName() + star.getType() + star.getPopularityIndex());
}
}

Your program runs forever because calling nextInt without changing the state of the scanner is going to cause an exception again and again: if the user did not enter an int, calling keyboard.nextInt() will not change what the scanner is looking at, so when you call keyboard.nextInt() in the next iteration, you'll get an exception.
You need to add some code to read the garbage the user entered after servicing an exception to fix this problem:
try {
...
} catch(Exception e) {
System.out.println("Error: invalid input:" + e.getMessage());
again = true;
keyboard.next(); // Ignore whatever is entered
}
Note: you do not need to rely on exceptions in this situation: rather than calling nextInt(), you could call hasNextInt(), and check if the scanner is looking at an integer or not.

java NoSuchElementException: no line found

edit:
adding the one of the methods called below, just in case the problem is with the method, not the loop.
Below is a switch menu, there are several cases in the switch. Each case calls a a public void method form another class, and completes successfully, is supposed to displays the menu method (method that prints menu options) and allow the user to select another option. Currently, after completing one case, the program showMenu() again, then breaks at instantly:
String menu = in.nextLine();
on the second iteration of the menu and sends back
java.util.NoSuchElementException: No line found
Question: I need the program to pause or something similar after showMenu(); to let the user input a menu selection, currently the menu displays and the program crashes instantly
Cheers
public class Menu {
public static char selection;
public static String quitting = "you dun son";
public static String errorMessage = "THAAAAATSS A menu WRRRAAAAAPPP";
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
try {
do {
showMenu();
String menu = in.nextLine();
if (menu.length() > 0) {
selection = menu.toLowerCase().charAt(0); // extract the first char of the line read
} else {
selection = '\0';
System.out.println("invalid input:\t" + selection);
System.out.println("Press enter to continue...");
}
switch (selection) {
case 'f':
FuelConsole fuelObject = new FuelConsole();
fuelObject.fuelCalc();
break;
case 'g':
GameConsole gameObject = new GameConsole();
gameObject.gameCalc();
break;
case 'q':
System.out.println("\nEnding Now\n");
System.exit(0);
break;
default:
System.out.println("Instruction is invalid");
}
} while (selection != 'Q' && selection != 'q');
{
System.out.println(quitting);
System.exit(0);
}
}catch (Exception e) {
System.out.println(errorMessage);
}
}
a test method:
public class FuelConsole {
public static String errorMessage = "THAAAAATSS A fuel calc WRRRRAAAAAPPPPPPPPPPPP";
public static Double acceptableCentsPerLitre = 16.00;
Scanner scan = new Scanner(System.in);
public void fuelCalc() {
try {
System.out.println("\nyou selected option 'f' --- here you will enter some information and find average fuel for ONE trip. ");
System.out.println("please enter the amount of fuel in litres:\n ");
float fuel = scan.nextFloat();
System.out.println("please enter the price of fuel in cents (not dollars and cents, only CENTS (lulz)):\n ");
int cent = scan.nextInt();
System.out.println("please enter the number of kilometers travelled on the tank:\n ");
float kilo = scan.nextFloat();
float returnAFC = afc(fuel, kilo);
float returnAC = ac(returnAFC, cent);
System.out.println("average consumption: \t" + returnAFC);
System.out.println("average cost: \t\t" + returnAC);
if (returnAC > acceptableCentsPerLitre) {
System.out.println("Average fuel is above 16c per litre");
} else {
System.out.println("Average fuel is below 16c per litre");
}
} catch (Exception e) {
System.out.println(errorMessage);
e.printStackTrace();
} finally {
scan.close();
}
}
public static float afc(float x, float z) {
float result = x / z;
return result;
}
public static float ac(float x, int y) {
float result = x * y;
return result;
}
}

I think the problem is that you create a new Scanner in the FuelConsole Class.
And you also close it in the finally block.
But when you call close() on scanner it also closes the underlaying InputStream too. (System.in in this case) And because your top-level Scanner uses the same InputStream, it cannot catch any more input from it.
The solution could be if you pass the top level scanner as an argument to other objects:
case 'f':
FuelConsole fuelObject = new FuelConsole();
fuelObject.fuelCalc(in);
break;
case 'g':
GameConsole gameObject = new GameConsole();
gameObject.gameCalc(in);
break;
and
public void fuelCalc(Scanner scan) {
try {
...
and delete the finally block

Validate the input using a while loop

I doing a little practice on Computer Science because when I leave the military I want to start taking classes on the basics of java. I'm a little stuck on this question i was wondering if i can get some assistance.
a program that allows the user to enter a character. The only valid values are 'A', 'M', and 'S'. Validate the input using a while loop so that if the user enters any value other than one of those 3 characters, an error message is displayed and the user is prompted for another value. Once the user has finally entered valid data, print the character they entered back to the screen.

You can look into this basic example
import java.util.Scanner;
public class Read {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
boolean isCheck = true;
while (isCheck) {
String str = sc.next();
switch (str) {
case "A":
System.out.println("A");
isCheck = false;
break;
case "M":
System.out.println("M");
isCheck = false;
break;
case "S":
System.out.println("S");
isCheck = false;
break;
default:
System.out.println("Not Valid : Enter next");
isCheck = true;
}
}
}
}

Reading you input within the loop will enforce repetitive reading of input.
public class Read {
public static void main(String[] args) {
boolean isCheck = true;
while(isCheck){
Scanner sc = new Scanner(System.in);
String str = sc.next();
switch (str) {
case "A":
System.out.println("A");
isCheck = false;
break;
case "M":
System.out.println("M");
isCheck = false;
break;
case "S":
System.out.println("S");
isCheck = false;
break;
default:
System.out.println("Not Valid : Enter next.");
isCheck = true;
}
}
}
}

Creating a Basic Java phone book

I'm just learning Java and trying to make a simple phone book. For this part I'm trying to prompt the user to choose one of the 3 options below.
public class PhoneBook {
public static void main (String[] args){
options();
/*This method prompts the user to enter phone number
String s;
Scanner in = new Scanner(System.in);
System.out.println("Enter Phone Number");
s = in.nextLine();
System.out.println("You entered phone number ");
System.out.println(s);*/
}
public static void options (){
//This method gives the user choices on what to do
char choice;
char enterNumber = 'n';
char showNumber = 's';
char closeBook = 'c';
String read;
String freeLine = "error";
Scanner keyboard = new Scanner(System.in);
while (true){
System.out.println("Please select from the following");
System.out.println("n to Enter the number");
System.out.println("s to Show the number ");
System.out.println("c to Close the Phone book");
read = keyboard.nextLine();
choice = read.charAt(0);
switch (choice) {
case 'n': enterNumber;
system.out.println();
case 's':showNumber;
system.out.println();
case 'c': closeBook;
break;
default: System.out.println("Invalid Entry");
}
}
}
}
When I compile it i get errors on lines 37, 39, and 41 saying "Error: not a statement". I feel like something is missing. If anyone can help it would be greatly appreciated.

I am assuming that with the following lines you want to achieve to print the letter n for enterNumber in the console?
case 'n': enterNumber;
system.out.println();
This is not correct Java syntax. You will have to pass the variable value to the System.out.println method call:
case 'n': System.out.println(enterNumber);
Also note that Java is case sensitive, so you have to spell System with a capital letter.
On a side note, you will want to break; after each of your case statements, otherwise the code of the following cases will be executed as well:
switch (choice) {
case 'n': System.out.println(enterNumber);
break;
case 's': System.out.println(showNumber);
break;
case 'c': System.out.println(closeBook);
break;
default: System.out.println("Invalid Entry");
}

you do not have to write variable after 'cast' statement.
Refer below code.
import java.util.Scanner;
public class PhoneBook {
public static void main (String[] args){
options();
/*This method prompts the user to enter phone number
String s;
Scanner in = new Scanner(System.in);
System.out.println("Enter Phone Number");
s = in.nextLine();
System.out.println("You entered phone number ");
System.out.println(s);*/
}
public static void options (){
//This method gives the user choices on what to do
char choice;
char enterNumber = 'n';
char showNumber = 's';
char closeBook = 'c';
String read;
String freeLine = "error";
Scanner keyboard = new Scanner(System.in);
while (true){
System.out.println("Please select from the following");
System.out.println("n to Enter the number");
System.out.println("s to Show the number ");
System.out.println("c to Close the Phone book");
read = keyboard.nextLine();
choice = read.charAt(0);
switch (choice) {
case 'n':
System.out.println();
case 's':
System.out.println();
case 'c':
break;
default: System.out.println("Invalid Entry");
}
}
}
}

I have made a special answer for you. I don't add additional explanation. It's a large answer. I tell more than you ask, but I've done my best to make a readable code, so that you can analyse step-by-step to understand what you need at least when trying to make a Phone Book (console test drive application). If you need more explanation, write under comments.
First make a PhoneEntry class:
import java.util.Objects;
public class PhoneEntry implements Comparable<PhoneEntry> {
// https://jex.im/regulex/#!embed=false&flags=&re=%5E%5Ba-zA-Z%5D%7B2%2C%7D((-%7C%5Cs)%5Ba-zA-Z%5D%7B2%2C%7D)*%24
private static final String NAME_PATTERN = "^[a-zA-Z]{2,}((\\-|\\s)[a-zA-Z]{2,})*$";
// https://jex.im/regulex/#!embed=false&flags=&re=%5E%5C%2B%3F%5Cd%2B((%5Cs%7C%5C-)%3F%5Cd%2B)%2B%24
private static final String NUMBER_PATTERN = "^\\+?\\d+((\\s|\\-)?\\d+)+$"; //^\+?\d+((\s|\-)?\d+)+$
private final String name;
private final String number;
public PhoneEntry(String name, String number) {
if (!name.matches(NAME_PATTERN) || !number.matches(NUMBER_PATTERN)) {
throw new IllegalArgumentException();
}
this.name = name;
this.number = number;
}
public String getName() {
return name;
}
public String getNumber() {
return number;
}
public boolean nameContainsIgnoreCase(String keyword) {
return (keyword != null)
? name.toLowerCase().contains(keyword.toLowerCase())
: true;
}
#Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
if (!(obj instanceof PhoneEntry)) {
return false;
}
PhoneEntry phoneEntry = (PhoneEntry) obj;
return name.equalsIgnoreCase(phoneEntry.name)
&& number.equalsIgnoreCase(phoneEntry.number);
}
#Override
public int hashCode() {
int hash = 5;
hash = 17 * hash + Objects.hashCode(this.name.toLowerCase());
hash = 17 * hash + Objects.hashCode(this.number.toLowerCase());
return hash;
}
#Override
public int compareTo(PhoneEntry phoneEntry) {
return name.compareToIgnoreCase(phoneEntry.name);
}
}
Then the test drive
public class TestDrive {
private static final String choices = "nspc";
enum Choice {
CREATE, READ, PRINT, CLOSE;
static Choice getChoice(char c) {
switch (c) {
case 'n':
return Choice.CREATE;
case 's':
return Choice.READ;
case 'p':
return Choice.PRINT;
case 'c':
return Choice.CLOSE;
}
return null;
}
}
// Main
public static void main(String[] args) {
Scanner kbd = new Scanner(System.in);
final Set<PhoneEntry> entries = new TreeSet<>();
Choice choice;
while ((choice = getChoice(kbd)) != Choice.CLOSE) {
switch (choice) {
case CREATE:
PhoneEntry entry = getPhoneEntry(kbd);
if (entry != null) {
entries.add(entry);
}
break;
case READ:
print(readEntries(entries, kbd));
break;
case PRINT:
print(entries);
break;
}
}
}
private static Choice getChoice(Scanner kbd) {
System.out.println("\nPlease select from the following");
System.out.println("\tn to Enter the number");
System.out.println("\ts to Show numbers by keyword ");
System.out.println("\tp to Show all numbers ");
System.out.println("\tc to Close the Phone book");
System.out.print("> ");
String input = kbd.nextLine();
Choice choice = null;
if (!input.isEmpty()
&& choices.contains(input.toLowerCase())
&& ((choice = Choice.getChoice(input.toLowerCase().charAt(0))) != null)) {
return choice;
}
System.out.println("ERR: INVALID ENTRY. TRY AGAIN");
return getChoice(kbd);
}
private static PhoneEntry getPhoneEntry(Scanner kbd) {
System.out.print("Type contact name: ");
String name = kbd.nextLine();
System.out.print("Type phone number: ");
String number = kbd.nextLine();
try {
return new PhoneEntry(name, number);
} catch (IllegalArgumentException ex) {
System.out.println("\nERR: WRONG ENTRY");
}
return null;
}
private static void print(Set<PhoneEntry> entries) {
System.out.println("\nPHONE NUMBERS\n");
entries.stream().forEach(entry -> {
System.out.printf("Name: %s%nPhone: %s%n%n",
entry.getName(), entry.getNumber());
});
}
private static Set<PhoneEntry> readEntries(Set<PhoneEntry> entries, Scanner kbd) {
System.out.print("Type keyword: ");
return entries.stream().filter(entry
-> entry.nameContainsIgnoreCase(kbd.nextLine()))
.collect(Collectors.toCollection(TreeSet::new));
}
}

Instead of enterNumber;, you have to write enterNumber();.
The parentheses mean: Call the method.

Java exception handling Do loop not working?

Here is the code:
package classes;
import java.util.*;
public class Introduction {
Scanner Input = new Scanner(System.in);
int classChoose;
boolean repeat = false;
public void Introduction() {
System.out.println("\t===THE QUEST FOR PERSEPOLIS===\tv 1.0\n");
System.out.println("Please choose a class: ");
System.out.print("(1)Elite Knight\t");
System.out.print("(2)Dawnguard\n");
System.out.print("(3)Archer\t\t\t");
System.out.print("(4)Barbarian\n");
System.out.print("(5)Mage\t\t\t");
System.out.print("(6)Swordsman\n");
System.out.println("(7)Crossbowman\t");
do {
try {
repeat = false;
classChoose = Input.nextInt();
while(classChoose < 1 || classChoose > 7) {
repeat = false;
System.out.println("Error. Enter a number between 1 and 7(inclusive).");
classChoose = Input.nextInt();
}
}
catch(InputMismatchException e) {
repeat = true;
System.err.println("Caught: "+e);
Input.nextLine();
}
}while(repeat = true);
switch(classChoose) {
case 1: chooseKnight();
break;
case 2: chooseGuard();
break;
case 3: chooseArcher();
break;
case 4: chooseBarbarian();
break;
case 5: chooseMage();
break;
case 6: chooseSwordsman();
break;
case 7: chooseCrossbowman();
break;
}
}
public static void chooseKnight() {
System.out.println("You have chosen the Elite Knight. You will be briefed and then you shall be set "
+"on your quest!");
}
static void chooseGuard() {
System.out.println("You have chosen the Dawnguard. You will be briefed and then you shall be set "
+"on your quest!");
}
static void chooseArcher() {
System.out.println("You have chosen the Archer. You will be briefed and then you shall be set "
+"on your quest!");
}
static void chooseBarbarian() {
System.out.println("You have chosen the Barbarian. You will be briefed and then you shall be set "
+"on your quest!");
}
static void chooseMage() {
System.out.println("You have chosen the Mage. You will be briefed and then you shall be set "
+"on your quest!");
}
static void chooseSwordsman() {
System.out.println("You have chosen the Swordsman. You will be briefed and then you shall be set "
+"on your quest!");
}
static void chooseCrossbowman() {
System.out.println("You have chosen the Crossbowman. You will be briefed and then you shall be set "
+"on your quest!");
}
}
Everytime I run it, the program prompts me to choose my class. After I enter my choice, the program does not go on to the switch statement below the do loop. Can someone help me fix this?
-Calvin

This is an assignment:
while(repeat = true); // Note single '=', not '=='
and the result of which will always be true, from section 15.26 Assignment Operators of the Java Language Specification:
At run time, the result of the assignment expression is the value of the variable
after the assignment has occurred.
Change to:
while(repeat);

while(repeat = true);
should be: -
while(repeat == true); // Or better: - while(repeat);
And in your catch, change Input.nextLine() to Input.next() : -
catch(InputMismatchException e) {
repeat = true;
System.err.println("Caught: "+e);
Input.nextLine(); // Change to Input.next()
}
And your instance variable should begin with a lowercase alphabet or an underscore.. So change Input to input.