Develop Reference

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

Breaking out of a loop by calling a method

I’m writing a small program that is asking that user to guess a number between 1 and 100. My idea was to make several methods one with game playGame(), one that shows menu showMenu(), one for statistic. I placed the menu inside a while loop in the main method hoping that every time a game is played it will the menu and ask the user for input. Most of it works fine buy I can’t get the program flow right.
Every time I finish a game, a new game starts. I think that the problem is in the while loop inside the many method. It works fine if I change:
public static void showMenu() {
Scanner input = new Scanner(System.in);
System.out.println("1. Play a game.");
System.out.println("2 Show statistics.");
System.out.println("3. Exit.\n");
System.out.println("Make a choise: ");
int selectMenu = input.nextInt();
while (true) {
switch (selectMenu) {
case 1:
playGame();
break;
case 2:
statistics();
break;
case 3:
System.exit(0);
break;
default:
System.out.println("Enter valid number:");
}
}
} //end showMenu
To:
public static void showMenu() {
Scanner input = new Scanner(System.in);
while (true) {
System.out.println("1. Play a game.");
System.out.println("2 Show statistics.");
System.out.println("3. Exit.\n");
System.out.println("Make a choise: ");
int selectMenu = input.nextInt();
switch (selectMenu) {
case 1:
playGame();
break;
case 2:
statistics();
break;
case 3:
System.exit(0);
break;
default:
System.out.println("Enter valid number:");
}
}
} //end showMenu
But I can’t understand why. In the firs example after the game is played a new game starts without showing the menu. It jumps directly to case: 1
Thanks a lot!
You can see the program below:
public class GuessTheNumber {
private static int gameCount;
private static int guessCount;
private static int highestNumber;
private static int lowestNumber;
public static void main(String[] args) {
while (true) {
showMenu();
}
} // end main
public static void playGame() {
int secretNumber, guess;
Scanner input = new Scanner(System.in);
SecureRandom rand = new SecureRandom();
secretNumber = rand.nextInt(100) + 1; //makes random number between 1 and 100
System.out.println(secretNumber);
System.out.println("Guess the secret mumber which is between 1 and 100.");
System.out.print("Make your guess: ");
guess = input.nextInt();
guessCount++;
highestNumber = guess;
lowestNumber = guess;
while (guess != secretNumber) {
// high or low logic
if (guess > secretNumber) {
System.out.println("The number is too high.");
}
else {
if (guess < secretNumber) {
System.out.println("The number is too low.");
}
}
System.out.print("Make a new guess: ");
guess = input.nextInt();
guessCount++;
//get highest and lowest number
if (guess > highestNumber) {
highestNumber = guess;
}
if (guess < lowestNumber) {
lowestNumber = guess;
}
} //end while
System.out.printf("Very good the right number was: %d%n", guess);
} //end playGame()
public static void showMenu() {
Scanner input = new Scanner(System.in);
System.out.println("1. Play a game.");
System.out.println("2 Show statistics.");
System.out.println("3. Exit.\n");
System.out.println("Make a choise: ");
int selectMenu = input.nextInt();
while (true) {
switch (selectMenu) {
case 1:
playGame();
break;
case 2:
statistics();
break;
case 3:
System.exit(0);
break;
default:
System.out.println("Enter valid number:");
}
}
} //end showMenu
public static void statistics() {
System.out.println("Games played: " + gameCount);
System.out.println("Total number of guesses: " + guessCount);
System.out.println("The highest number: " + highestNumber);
System.out.println("The lowest number: " + lowestNumber);
}
} //end class GuessTheNumber

As this seems like a homework project, here is a quick tip for finding loop issues - simply add System.out.println("") checks inside and outside of all loop and logic conditions.
EG). System.out.println("Before While True);
System.out.println("Inside Case 1");
System.out.println("Inside Case 2");
You will save yourself a ton of time as you'll be able to tell where your logic is breaking.
As a hint, take a look at int selectMenu = input.nextInt();. I would recommend printing the value of selectMenu using my advice above. You might be surprised to see what's assigned there.

Use switch case within while loop

I'm trying to code simple calculator (all in one) using Switch cases in java. I came up with following code so far. However I'm stuck with while loop. I want to keep showing main menu after each case execution until user decides to exit the program.
public static void main(String[] args)
{
Scanner s=new Scanner(System.in);
System.out.println("Main Menu:");
System.out.println("1. Addition");
System.out.println("2. Substraction");
System.out.println("3. Multipication");
System.out.println("4. Division");
System.out.println("Enter your choice: ");
int i=s.nextInt();
System.out.println("ENTER FIRST NUMBER ");
int a=s.nextInt();
System.out.println("ENTER SECOND NUMBER ");
int b=s.nextInt();
int result=0;
switch(i)
{
case 1:
result=a+b;
break;
case 2:
result=a-b;
break;
case 3:
result=a*b;
break;
case 4:
result=a/b;
break;
default:
System.out.println("Wrong Choice.");
}
System.out.println("Answer is "+result);
}
}
Above code works fine. Program ends itself after execution of user selected choice. I want to put main menu on a repeat.

Add a while loop like this:
public static void main(String[] args) {
// Moved this outside the while loop as davidxxx pointed out +1
Scanner s = new Scanner(System.in);
while (true) {
System.out.println("Main Menu:");
System.out.println("1. Addition");
System.out.println("2. Substraction");
System.out.println("3. Multipication");
System.out.println("4. Division");
System.out.println("Enter your choice: ");
int i = s.nextInt();
System.out.println("ENTER FIRST NUMBER ");
int a = s.nextInt();
System.out.println("ENTER SECOND NUMBER ");
int b = s.nextInt();
int result = 0;//'result' will store the result of operation
switch (i) {
case 1:
result = a + b;
break;
case 2:
result = a - b;
break;
case 3:
result = a * b;
break;
case 4:
result = a / b;
break;
default:
System.out.println("Wrong Choice.");
}
System.out.println("Answer is " + result);
System.out.println("Go again?");
String goAgain = s.next();
if (!goAgain.equals("y")) {
break;
}
}
}

Try this:
import java.util.Scanner;
public class Calculator {
private static final String EXIT = "EXIT";
public static void main(String[] args) {
Calculator calc = new Calculator();
Scanner s = new Scanner(System.in);
while (true) {
String res = calc.runCalc(s);
if (res.equals(EXIT)) {
break;
} else {
System.out.println(res);
}
}
}
private String runCalc(Scanner s) {
System.out.println("Main Menu:");
System.out.println("1. Addition");
System.out.println("2. Substraction");
System.out.println("3. Multipication");
System.out.println("4. Division");
System.out.println("5. Exit");
System.out.println("Enter your choice: ");
int i = s.nextInt();
if (i == 5) {
return EXIT;
}
System.out.println("ENTER FIRST NUMBER ");
int a = s.nextInt();
System.out.println("ENTER SECOND NUMBER ");
int b = s.nextInt();
int result = 0;// 'result' will store the result of operation
switch (i) {
case 1:
result = a + b;
break;
case 2:
result = a - b;
break;
case 3:
result = a * b;
break;
case 4:
result = a / b;
break;
default:
return "Wrong Choice.";
}
return "Answer is " + result;
}
}

There is more than one way to achieve this, you can use
while loop.
do-while loop.
for loop.
I think do-while loop is better for your situation. Because either user wants to continue or not you have to proceed one time(before loop false). And you do not want to use another variable for quit the loop.
public static void main(String[] args)
{
Scanner s=new Scanner(System.in);
int result=0;
do{
System.out.println("Main Menu:");
System.out.println("-1. complete and calculate");
System.out.println("1. Addition");
System.out.println("2. Substraction");
System.out.println("3. Multipication");
System.out.println("4. Division");
System.out.println("Enter your choice: ");
int i=s.nextInt();
if(i ==-1){
System.out.println("Answer is "+result);
return;
}
System.out.println("ENTER FIRST NUMBER ");
int a=s.nextInt();
System.out.println("ENTER SECOND NUMBER ");
int b=s.nextInt();
switch(i)
{
case 1:
result=a+b;
break;
case 2:
result=a-b;
break;
case 3:
result=a*b;
break;
case 4:
result=a/b;
break;
default:
System.out.println("Wrong Choice.");
break;
}
}while(true);
}

switch case in implementation of stack using array in java

import java.io.*;
import java.util.*;
public class Stack1{
static final int MAX=100;
int top=-1;
int[] stack=new int[MAX];
public static void main(String args[])
{
Stack1 s1=new Stack1();
int opt, val;
System.out.println("1. PUSH ");
System.out.println("2. POP ");
System.out.println("3. PEEP ");
System.out.println("4. DISPLAY STACK ");
System.out.println("5. EXIT ");
System.out.println("\n Enter Your Option: ");
Scanner s=new Scanner(System.in);
opt=s.nextInt();
do{
switch(opt)
{
case 1: System.out.println("Enter the value to be added to the stack: ");
val=s.nextInt();
s1.push(val);
break;
case 2: s1.pop();
break;
/*
case 3: s1.peep();
break; */
case 4: s1.display();
break;
}
}while(opt!=5);
}
public void push(int val)
{
if(top==MAX-1)
{
System.out.println("Stack is FULL!");
}
else
{
top++;
stack[top]=val;
System.out.println("Element added to the stack is: "+val);
display();
}
}
public void pop()
{
int x;
if(top==-1)
{
System.out.println("Stack is EMPTY!");
}
else
{
x=stack[top];
System.out.println("The element deleted from the stack is: "+x);
top--;
display();
}
}
public void peep()
{
int n;
n=stack[top];
System.out.println("The value at the top of the stack is: "+n);
}
public void display()
{
int i;
if(top==-1)
System.out.println("STACK IS EMPTY!");
else
{
for(i=0; i<=top; i++)
System.out.println("The elements in the stack are: "+stack[i]);
}
}
}
I wrote this java code to implement stack. But once I select any option, only that method gets executed and the program ends. I want the program to provide me to enter another option once the current method is executed. What should I do?

As #LordWilmore pointed out in his comment, the opt value will be set just once causing program to spin forever in a corresponding case (unless the value is 5). Moving opt = s.nextInt(); inside loop will fix the issue.
do {
System.out.println("Enter Your Option: ");
opt = s.nextInt();
switch(opt) {
//...
}
} while (opt != 5);

You can modify your main method in a manner like this:
public static void main(String args[]){
int option;
Scanner sc = new Scanner(System.in);
MyStack1 s = new MyStack1();
while(true){
System.out.println("Enter the choice You want to perform on the stack: ");
System.out.println(" 1. push \n 2. Pop \n 3. Display \n 4. peep \n 5. Exit");
System.out.println("Enter your option: ");
option = sc.nextInt();
switch(option){
case 1: System.out.println("Enter the element you want to push into the stack: ");
s.push(sc.nextInt());
break;
case 2: s.pop();
break;
case 3: System.out.println("Displaying the stack contents: ");
s.display();
break;
case 4: System.out.println("The top element in the stack is: ");
s.peek();
break;
case 5: System.out.println("You selected Exit!!");
break;
default: System.out.println("Wrong choice!! Please enter a valid option!!");
return;
}
}
}

Exiting switch back to main method

I have a method which uses a switch statement to give the user options to select, once they have selected an option and the code in the case has been executed how do I get back into the main method which offers another menu?
Part of my code:
static void modifyStudent() {
System.out.println("Wish student would you like to change?");
for(int i=0;i<10;i++){
System.out.println(i + ": " + studentNamesArray[i]);
}
int studentChoice = input.nextInt();
System.out.println("1: Change name.");
....
int detailChange = input.nextInt();
switch (detailChange) {
case 1:
String newName = input.next();
studentNamesArray[studentChoice] = newName;
break;
....
}
public static void main(String[] args) {
while (1 == 1) {
System.out.println("Please select an option:");
System.out.println("1: Add a student.");
....
int choice = input.nextInt();
switch (choice) {
case 1:
....
}
EDIT (full code requested):
/**
* User: Colin Shewell
* Date: 26/11/13
* Time: 10:32
*/
import java.util.Scanner;
import java.util.Arrays; //REMOVE THIS!!!
public class StudentMarks {
static Scanner input = new Scanner(System.in);
static String[] studentNamesArray = new String[10];
static int[][] studentMarksArray = new int[10][3];
static int nameArrayCount, markArrayCount = 0;
static int markOne, markTwo, markThree;
static String studentName;
static void printArrays(){
System.out.println(Arrays.toString(studentNamesArray));
for (int index=0;index<10;index++)
{
System.out.println(studentMarksArray[index][0]);
System.out.println(studentMarksArray[index][1]);
System.out.println(studentMarksArray[index][2]);
}
}
static void addStudent() {
if (nameArrayCount < 10) {
System.out.println("Enter the student's name in the following format - surname, forename: ");
studentName = input.next();
studentNamesArray[nameArrayCount] = studentName;
nameArrayCount = nameArrayCount + 1;
}
else if (nameArrayCount == 10) {
System.out.println("******Array is full, please delete a student before adding another.*****");
}
if (markArrayCount < 10){
System.out.println("Enter the first mark: ");
markOne = input.nextInt();
System.out.println("Enter the second mark: ");
markTwo = input.nextInt();
System.out.println("Enter the third mark: ");
markThree = input.nextInt();
studentMarksArray[markArrayCount][0] = markOne;
studentMarksArray[markArrayCount][1] = markTwo;
studentMarksArray[markArrayCount][2] = markThree;
markArrayCount = markArrayCount + 1;
}
}
static void modifyStudent() {
System.out.println("Wish student would you like to change?");
for(int i=0;i<10;i++){
System.out.println(i + ": " + studentNamesArray[i]);
}
int studentChoice = input.nextInt();
System.out.println("1: Change name.");
System.out.println("2: Change first mark.");
System.out.println("3: Change second mark.");
System.out.println("4: Change third mark.");
System.out.println("5: Change all marks.");
int detailChange = input.nextInt();
switch (detailChange) {
case 1:
System.out.println("Enter the new student name.");
String newName = input.next();
studentNamesArray[studentChoice] = newName;
return;
case 2:
System.out.println("Enter the new mark for mark one.");
int newMarkOne = input.nextInt();
studentMarksArray[studentChoice][0] = newMarkOne;
return;
case 3:
//two
break;
case 4:
//three
break;
case 5:
//all
break;
default:
System.exit(0);
break;
}
}
public static void main(String[] args) {
while (true) {
System.out.println("Please select an option:");
System.out.println("1: Add a student.");
System.out.println("2: Modify the details of an existing student.");
System.out.println("3: Delete an existing student.");
System.out.println("4: Sort in alphabetical order by name.");
System.out.println("5: Output the student name and corresponding marks in ascending name order.");
System.out.println("6: Output the student name and corresponding marks in descending name order.");
System.out.println("7: Display the student with the highest average mark.");
System.out.println("8: Display the student with the lowest average mark.");
System.out.println("9: Display the average score of all students recorded.");
System.out.println("10: Exit.");
int choice = input.nextInt();
switch (choice) {
case 1:
addStudent();
System.out.println(Arrays.toString(studentNamesArray));
break;
case 2:
modifyStudent();
break;
case 3:
printArrays();
break;
/* case 4:
sortAlphabetical();
break;
case 5:
outputNameMarksAsc();
break;
case 6:
outputNameMarksDsc();
break;
case 7:
highestStudentAvgMark();
break;
case 8:
lowestStudentAvgMark();
break;
case 9:
displayAvgScore();
break; */
case 10:
System.exit(0);
break;
default:
System.exit(0);
break;
}
}
}
}

Just return to the main method. return just exits the method and continues executing code from the line it was called.
case 1:
String newName = input.next();
studentNamesArray[studentChoice] = newName;
return; //exits this method
//break; <-- not needed after a return!

Your code will run in an infinite loop, you can make it run with a conditional flag like this
boolean isRunning = true;
while (isRunning) {
System.out.println("Please select an option:");
System.out.println("1: Add a student.");
....
int choice = input.nextInt();
switch (choice) {
case 1:
isRunning = false;
//your code for case 1
....
}
//rest of the code in main executes now
This will exit the while loop back to the main method