problem with performing Scanner class in java - java

I am running into a problem, that everytime the do{...} while(...) loop runs the second time, the first iteration of for(...) loop does not execute the following statement
array[o] = scan1.nextLine();.
This is what i have tried so far:
import java.util.Scanner;
public class test
{
public static void main(String args[]) throws Exception
{
int columns=2;
String array[]=new String[10];
char ins_check='y';
Scanner scan1=new Scanner(System.in);
do {
System.out.println("Enter the value");
for (int o = 1; o <= columns; o++) {
System.out.println("Enter the value");
array[o] = scan1.nextLine();
}
System.out.println("record inserted");
System.out.println("Do you want to insert again?(y/n)");
ins_check= (char) System.in.read();
}while(ins_check != 'n');
}
}


While several commenters told you what to do and what not to do, they didn't answer your question about the reason why this is occuring.
the first time of for loop does not execute this statement: array[o] = scan1.nextLine();
You are mistaken - the statement is well executed, it's only that an empty line is read. And this is because after the prompt "Do you want to insert again?(y/n)" you entered a line consisting of the two characters y \n, and System.in.read() read only one byte of data (the y), leaving the newline character \n in the input stream. The subsequent scan1.nextLine() gets this \n and returns the empty line.


Here is still someone who post answer faster then me. Take a look on reply from Amali, thats right answer :) this should work fine:
import java.util.Scanner;
public class test
{
public static void main(String args[]) throws Exception
{
Scanner scan1=new Scanner(System.in);
String array[]=new String[10];
String ins_check="y";
int columns=9;
do {
for (int o = 0; o <= columns; o++) {
System.out.printf("Enter the value for array[%s]",o);
array[o] = scan1.nextLine();
}
System.out.println("record inserted");
System.out.println("Do you want to insert again?(y/n)");
ins_check= scan1.nextLine();
}while(ins_check.equals("y"));
System.out.println("end");
}
}

Related

Problem with first java project with Whilebreakwithloop

Write a simple program that uses a break statement to end the while loop where the condition in while loop is always true. Test the user input and if it is zero then use a break to exit or come out of the loop.
Do I need to add any value to execute the code?
import java.util.Scanner;
class WhileLoopWithBreak {
public static void main(String[] args) {
int n;
Scanner input = new Scanner(System.in);
while () {
continue;
} else {
break;
}
}
}

Check this:
int n;
Scanner input = new Scanner(System.in);
while (true) {
# Using string as user can enter anything.
String text = input.nextLine();
# Trimming the input to remove white-space characters.
if (text.trim().equals("0")){
break;
}
}

java while loop throwing exception

the first line takes the size of the array to follow.The array's digits are checked to see if they can form a ambiguous permutation.
public class Codechef2 {
public static void main(String[] args) {
Scanner input=new Scanner(System.in);
int intnum=10;
intnum=input.nextInt();
input.nextLine();
String a[]=new String[100000];
int count=0;
int i=0;
While(intnum>0)
{
a[i]=input.nextLine();
String arr[]=a[i].split(" ");
int aj[]=new int[arr.length];
int k=0;
for(int j=0;j<arr.length;j++)
{
aj[Integer.parseInt(arr[k])]=j+1;
k++;
}
for(int l=0;l<arr.length;l++)
{
if(aj[l]==Integer.parseInt(arr[l]))
count++;
}
if(count==arr.length)
System.out.println("ambiguous permutation");
else
System.out.println("Not ambiguous permutation");
intnum=input.nextInt();
}
}
}

EDIT:
Again: pleas post a compilable code:
//wrong
//While(intnum>0)
while(intnum>0)
Also:
//you need to print a msg so the user knows that he / she
//needs to input and tell the user what to input
System.out.println("Please enter ....");
input.nextLine();
The code has many errors.
For example :
String aj[]=new aj[arr.length]; //will not compile
While(intnum>0) //will not compile
a[i]=input.nextLine(); //will not compile. i is defined later.
aj[arr[k]]=i+1; //wrong : aj[] is a String. i+1 is an int.
Fix them and post a compilable code.

Code below the while loop is not executed until the conditions of the while loop are met.

Java Scanner delimiter and System.in

I have some problem when I ask the user to input some numbers and then I want to process them. Look at the code below please.
To make this program works properly I need to input two commas at the end and then it's ok. If I dont put 2 commas at the and then program doesnt want to finish or I get an error.
Can anyone help me with this? What should I do not to input those commas at the end
package com.kurs;
import java.util.Scanner;
public class NumberFromUser {
public static void main(String[] args) {
String gd = "4,5, 6, 85";
Scanner s = new Scanner(System.in).useDelimiter(", *");
System.out.println("Input some numbers");
System.out.println("delimiter to; " + s.delimiter());
int sum = 0;
while (s.hasNextInt()) {
int d = s.nextInt();
sum = sum + d;
}
System.out.println(sum);
s.close();
System.exit(0);
}
}

Your program hangs in s.hasNextInt().
From the documentation of Scanner class:
The next() and hasNext() methods and their primitive-type companion
methods (such as nextInt() and hasNextInt()) first skip any input that
matches the delimiter pattern, and then attempt to return the next
token. Both hasNext and next methods may block waiting for further
input.
In a few words, scanner is simply waiting for more input after the last integer, cause it needs to find your delimiter in the form of the regular expression ", *" to decide that the last integer is fully typed.
You can read more about your problem in this discussion:
Link to the discussion on stackoverflow
To solve such problem, you may change your program to read the whole input string and then split it with String.split() method. Try to use something like this:
import java.util.Scanner;
public class NumberFromUser {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
String[] tokens = sc.nextLine().split(", *");
int sum = 0;
for (String token : tokens) {
sum += Integer.valueOf(token);
}
System.out.println(sum);
}
}

Try allowing end of line to be a delimiter too:
Scanner s = new Scanner(System.in).useDelimiter(", *|[\r\n]+");

I changed your solution a bit and probably mine isn't the best one, but it seems to work:
Scanner s = new Scanner(System.in);
System.out.println("Input some numbers");
int sum = 0;
if (s.hasNextLine()) {
// Remove all blank spaces
final String line = s.nextLine().replaceAll("\\s","");
// split into a list
final List<String> listNumbers = Arrays.asList(line.split(","));
for (String str : listNumbers) {
if (str != null && !str.equals("")) {
final Integer number = Integer.parseInt(str);
sum = sum + number;
}
}
}
System.out.println(sum);

look you can do some thing like this mmm.
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
System.out.println("Input some numbers");
System.out.println("When did you to finish and get the total sum enter ,, and go");
boolean flag = true;
int sum = 0;
while (s.hasNextInt() && flag) {
int d = s.nextInt();
sum = sum + d;
}
System.out.println(sum);
}

When the program loops it prints the line "Enter your name (first and last): " twice?

So in the program I ask the user whether they want to rerun the program but when it does it prints the line "Enter your name," followed by a space, twice. Can someone please help me find the cause of this? It doesn't happen when you run it the first time by the way.
import java.util.Scanner;
public class PirateName
{
static Scanner input = new Scanner(System.in);
static String[]firstNames = {"Captain", "Dirty", "Squidlips", "Bowman", "Buccaneer",
"Two toes", "Sharkbait", "Old", "Peg Leg", "Fluffbucket",
"Scallywag", "Bucko", "Deadman", "Matey", "Jolly",
"Stinky", "Bloody", "Miss", "Mad", "Red", "Lady",
"Shipwreck", "Rapscallion", "Dagger", "Landlubber", "Freebooter"};
static String[]secondNames =
{"Creeper","Jim","Storm","John","George","Money","Rat","Jack","Legs",
"Head","Cackle","Patch","Bones","Plank","Greedy","Mama","Spike","Squiffy",
"Gold","Yellow","Felony","Eddie","Bay","Thomas","Spot","Sea"};
static String[]thirdNames =
{"From-the-West","Byrd","Jackson","Sparrow","Of-the-Coast","Jones","Ned-Head",
"Bart","O'Fish","Kidd","O'Malley","Barnacle","Holystone","Hornswaggle",
"McStinky","Swashbuckler","Sea-Wolf","Beard","Chumbucket","Rivers","Morgan",
"Tuna-Breath","Three Gates","Bailey","Of-Atlantis","Of-Dark-Water"};
static String[] letters = {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o",
"p","q","r","s","t","u","v","w","x","y","z"};
public static void main(String[] args) {
System.out.println("Welcome to the pirate name generator");
System.out.println("");
boolean running = true;
while(running){
nameGenerator();
}
}
public static boolean nameGenerator()
{
boolean rerun = false;
int x = 0;
System.out.println("Enter your name (first and last): ");
String userName = input.nextLine();
System.out.println("");
try{
String first = userName.substring(0,1);
for (int i=0;i <= 25 ; i++)
{
if(first.equalsIgnoreCase(letters[i]))
{
first = firstNames[i];
}
}
String last1 = userName.substring(userName.indexOf(' ')+1);
for (int i=0;i <= 25 ; i++)
{
if(last1.substring(0,1).equalsIgnoreCase(letters[i]))
{
last1 = secondNames[i];
}
}
String last2 = userName.substring(userName.length() - 1);
for (int i=0;i <= 25 ; i++)
{
if(last2.equalsIgnoreCase(letters[i]))
{
last2 = thirdNames[i];
}
}
System.out.println("Your pirate name is: ");
System.out.println("");
System.out.println(first+" "+last1+" "+last2);
System.out.println("");
System.out.println("Would you like to try again? (Type 1 for yes, 2- no)");
int a = input.nextInt();
if (a==2)
{
rerun = false;
System.out.println("Good Bye!");
return rerun;
}
else
{
rerun = true;
}
return rerun;
}
catch (Exception e){
System.out.println(" ");
}
return rerun;
}
}

I see at least three problems.
At the end of the method, when you read the value of a, you're pulling an integer from the Scanner, but you're not pulling out the newline character that follows the integer. This means that next time you call nextLine(), all you'll get is a blank line. The cure for this is to add an extra input.nextLine() immediately after input.nextInt().
You're catching exceptions and throwing them away, without even printing their stack traces. That means that if your program does encounter a problem, you'll never find out any information about the problem.
You're not using the value rerun outside the nameGenerator method. When you call it, you're checking if running is true, but running will never change, so you'll just go on calling it forever. So you probably want to change the code that calls it to this.
boolean shouldRun = true;
while (shouldRun) {
shouldRun = nameGenerator();
}

It looks like you are using the input scanner for entering both ints and strings. You should use two separate scanners, or change it so that input is brought in with .nextLine() and then changed to an integer.
The problem is you enter two characters when deciding to try again. The first is the int, the second is the character. The second character is not an integer, so it is left in the buffer. Then when you get input a second time, you are using a scanner that already has characters in the buffer. So it processes the buffer and reads the left over char as an empty line.
http://www.java-forums.org/new-java/24042-input-nextline.html

How to skip a block in Java?

In the program given I have to make sure that if two consequtive characters are the same. I shouldn't increase the value of the variable (Count)... I have tried "break;", but that skips me out of the "for loop" which is very counter-productive. How can I skip the given part and still continue the "for loop"?
Currently my output for "Hello//world" is 3. It should be 2 (the '/' indicates a ' '(Space)).
Code
import java.util.Scanner;
class CountWordsWithEmergency
{
public static void main()
{
Scanner input = new Scanner(System.in);
System.out.println("Please input the String");
String inp = input.nextLine();
System.out.println("thank you");
int i = inp.length();
int count = 1;
for(int j=0;j<=i-1;j++) //This is the for loop I would like to stay in.
{
char check = inp.charAt(j);
if(check==' ')
{
if((inp.charAt(j+1))==check) //This is the condition to prevent increase for
//count variable.
{
count = count; //This does not work and neither does break;
}
count++;
}
}
System.out.println("The number of words are : "+count);
}
}

You can use the keyword continue in order to accomplish what you are trying to do.
However you can also inverse your conditional test and use count++ only if it is different (!= instead of == in your if) and do nothing otherwise

if ((inp.charAt(j+1)) != check) {
count++;
}

The word you are looking for is "continue".

Try this:
if ((inp.charAt(j+1)) != check) {
count++;
}
Increment the value of count by checking with !=.

Try using continue where you want to skip an block.

Use "continue;" when you want to break the current iteration.

continue is a keyword in java programming used to skip the loop or block of code and reexecutes the loop with new condition.
continue statement is used only in while,do while and for loop.

You may want to use the continue keyword, or modify the logic a little bit:
import java.util.Scanner;
class CountWordsWithEmergency
{
public static void main()
{
Scanner input = new Scanner(System.in);
System.out.println("Please input the String");
String inp = input.nextLine();
System.out.println("thank you");
int i = inp.length();
int count = 1;
for(int j=0;j<=i-1;j++) //This is the for loop I would like to stay in.
{
char check = inp.charAt(j);
if(check==' ')
{
if((inp.charAt(j+1))!=check)
{
count++;
}
}
}
System.out.println("The number of words are : "+count);
}
}
Edit:
You may want to use the split method of the String class.
int wordsCount = str.split(' ').length;
Hope it helps :)

The following should work.
import java.util.Scanner;
class CountWordsWithEmergency
{
public static void main()
{
Scanner input = new Scanner(System.in);
System.out.println("Please input the String");
String inp = input.nextLine();
System.out.println("thank you");
int i = inp.length();
int count = 1;
for(int j=0;j<=i-1;j++) //This is the for loop I would like to stay in.
{
char check = inp.charAt(j);
if(check==' ')
{
if((inp.charAt(j+1))==check) //This is the condition to prevent increase for
//count variable.
{
continue;
}
count++;
}
}
System.out.println("The number of words are : "+count);
}
}

Categories