`Scanner scanner = new Scanner(System.in);
System.out.println("Enter your name:");
String userName = scanner.nextLine();
if (scanner.hasNextDouble()){
System.out.println("You can't enter numbers");
}`
Here i can't print "You can't enter numbers". Or is there any other option to restrict user to input numbers?
You can try out something like below
public static void main(String[] args) {
boolean validUsername = false;
String regexForNumbers = ".*\\d.*";
Scanner scanner = new Scanner(System.in);
System.out.println("Enter your name:");
while (!validUsername) {
String userName = scanner.nextLine();
if(userName.matches(regexForNumbers)){
System.out.println("Username Can not contain numbers");
System.out.println("Please Enter username again:");
}else{
validUsername = true;
}
}
}
Here String regexForNumbers = ".*\\d.*"; will check whether the username contains a number,and you can expect something like this,
Enter your name:
maneesha123
Username Can not contain numbers
Please Enter username again:
123
Username Can not contain numbers
Please Enter username again:
maneesha
Keep it simple, use the String#matches() method with a small Regular Expression (regex) to make sure numerical digits have not been supplied. The "\\D" regex does exactly that, for example:
Scanner scanner = new Scanner(System.in);
String userName = "";
while (userName.isEmpty()) {
System.out.println();
System.out.print("Enter your User name: --> ");
userName = scanner.nextLine();
// Anything is acceptable 'except' numerical digits.
if (!userName.matches("\\D+")) {
System.err.println("Invalid name supplied (" + userName + ")!.\n"
+ "Numerical digits are not permitted! Try again...");
userName = "";
}
}
System.out.println("Acceptable: " + userName);
This program needs to print a.b.c. but it prints a.b.c...
How do I eliminate the last dot in output.
The program has to work with user ending loop with "."
import java.util.Scanner;
public class dots1 {
public static void main(String args[]) {
Scanner s = new Scanner(System.in);
String input;
String output = "";
System.out.println("Hello! I print out an acronym. ");
do {
System.out.println("Please Enter a Character");
input = s.nextLine();
output = output+input+".";
} while (!input.equals("."));
System.out.println(output);
}
}
Because your exit condition is "." and you add it to output and add another dot. Try following:
public static void main(String args[]) {
Scanner s = new Scanner(System.in);
String input = "";
String output = "";
System.out.println("Hello! I print out an acronym. ");
while (true) {
System.out.println("Please Enter a Character");
input = s.nextLine();
if(input.equals("."))
break;
output = output + input + ".";
} ;
System.out.println(output);
}
I use a little trick using a simple check to see if its not the first read.
boolean isFirst=true;
do{
System.out.println("Please Enter a Character");
input = s.nextLine();
if(!isFirst) output="."+output;
isFirst=false;
output = output+input;
}while(!input.equals("."));
Instead of the do... while, you should use the the while function.
while (!input.equals(".") {
}
You have to use substring function in java and remove the last character of the String.
your loop end while you enter a dot in input.
Example given below.
Try this
import java.util.Scanner;
public class dots1 {
Scanner s = new Scanner(System.in);
String input;
String output = "";
System.out.println("Hello! I print out an acronym. ");
do{
System.out.println("Please Enter a Character");
input = s.nextLine();
output = output+input+".";
}while(!input.contains("."));
System.out.println(output.substring(0, output.length() - 2));
}
}
Output of Single Input
output of Multiple Inputs
How could I read input from the console using the Scanner class? Something like this:
System.out.println("Enter your username: ");
Scanner = input(); // Or something like this, I don't know the code
Basically, all I want is have the scanner read an input for the username, and assign the input to a String variable.
A simple example to illustrate how java.util.Scanner works would be reading a single integer from System.in. It's really quite simple.
Scanner sc = new Scanner(System.in);
int i = sc.nextInt();
To retrieve a username I would probably use sc.nextLine().
System.out.println("Enter your username: ");
Scanner scanner = new Scanner(System.in);
String username = scanner.nextLine();
System.out.println("Your username is " + username);
You could also use next(String pattern) if you want more control over the input, or just validate the username variable.
You'll find more information on their implementation in the API Documentation for java.util.Scanner
Scanner scan = new Scanner(System.in);
String myLine = scan.nextLine();
Reading Data From The Console
BufferedReader is synchronized, so read operations on a BufferedReader can be safely done from multiple threads. The buffer size may be specified, or the default size(8192) may be used. The default is large enough for most purposes.
readLine() « just reads data line by line from the stream or source. A line is considered to be terminated by any one these: \n, \r (or) \r\n
Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace(\s) and it is recognised by Character.isWhitespace.
« Until the user enters data, the scanning operation may block, waiting for input.
« Use Scanner(BUFFER_SIZE = 1024) if you want to parse a specific type of token from a stream.
« A scanner however is not thread safe. It has to be externally synchronized.
next() « Finds and returns the next complete token from this scanner.
nextInt() « Scans the next token of the input as an int.
Code
String name = null;
int number;
java.io.BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
name = in.readLine(); // If the user has not entered anything, assume the default value.
number = Integer.parseInt(in.readLine()); // It reads only String,and we need to parse it.
System.out.println("Name " + name + "\t number " + number);
java.util.Scanner sc = new Scanner(System.in).useDelimiter("\\s");
name = sc.next(); // It will not leave until the user enters data.
number = sc.nextInt(); // We can read specific data.
System.out.println("Name " + name + "\t number " + number);
// The Console class is not working in the IDE as expected.
java.io.Console cnsl = System.console();
if (cnsl != null) {
// Read a line from the user input. The cursor blinks after the specified input.
name = cnsl.readLine("Name: ");
System.out.println("Name entered: " + name);
}
Inputs and outputs of Stream
Reader Input: Output:
Yash 777 Line1 = Yash 777
7 Line1 = 7
Scanner Input: Output:
Yash 777 token1 = Yash
token2 = 777
There is problem with the input.nextInt() method - it only reads the int value.
So when reading the next line using input.nextLine() you receive "\n", i.e. the Enter key. So to skip this you have to add the input.nextLine().
Try it like that:
System.out.print("Insert a number: ");
int number = input.nextInt();
input.nextLine(); // This line you have to add (it consumes the \n character)
System.out.print("Text1: ");
String text1 = input.nextLine();
System.out.print("Text2: ");
String text2 = input.nextLine();
There are several ways to get input from the user. Here in this program we will take the Scanner class to achieve the task. This Scanner class comes under java.util, hence the first line of the program is import java.util.Scanner; which allows the user to read values of various types in Java. The import statement line should have to be in the first line the java program, and we proceed further for code.
in.nextInt(); // It just reads the numbers
in.nextLine(); // It get the String which user enters
To access methods in the Scanner class create a new scanner object as "in". Now we use one of its method, that is "next". The "next" method gets the string of text that a user enters on the keyboard.
Here I'm using in.nextLine(); to get the String which the user enters.
import java.util.Scanner;
class GetInputFromUser {
public static void main(String args[]) {
int a;
float b;
String s;
Scanner in = new Scanner(System.in);
System.out.println("Enter a string");
s = in.nextLine();
System.out.println("You entered string " + s);
System.out.println("Enter an integer");
a = in.nextInt();
System.out.println("You entered integer " + a);
System.out.println("Enter a float");
b = in.nextFloat();
System.out.println("You entered float " + b);
}
}
import java.util.Scanner;
public class ScannerDemo {
public static void main(String[] arguments){
Scanner input = new Scanner(System.in);
String username;
double age;
String gender;
String marital_status;
int telephone_number;
// Allows a person to enter his/her name
Scanner one = new Scanner(System.in);
System.out.println("Enter Name:" );
username = one.next();
System.out.println("Name accepted " + username);
// Allows a person to enter his/her age
Scanner two = new Scanner(System.in);
System.out.println("Enter Age:" );
age = two.nextDouble();
System.out.println("Age accepted " + age);
// Allows a person to enter his/her gender
Scanner three = new Scanner(System.in);
System.out.println("Enter Gender:" );
gender = three.next();
System.out.println("Gender accepted " + gender);
// Allows a person to enter his/her marital status
Scanner four = new Scanner(System.in);
System.out.println("Enter Marital status:" );
marital_status = four.next();
System.out.println("Marital status accepted " + marital_status);
// Allows a person to enter his/her telephone number
Scanner five = new Scanner(System.in);
System.out.println("Enter Telephone number:" );
telephone_number = five.nextInt();
System.out.println("Telephone number accepted " + telephone_number);
}
}
You can make a simple program to ask for the user's name and print whatever the reply use inputs.
Or ask the user to enter two numbers and you can add, multiply, subtract, or divide those numbers and print the answers for user inputs just like the behavior of a calculator.
So there you need the Scanner class. You have to import java.util.Scanner;, and in the code you need to use:
Scanner input = new Scanner(System.in);
input is a variable name.
Scanner input = new Scanner(System.in);
System.out.println("Please enter your name: ");
s = input.next(); // Getting a String value
System.out.println("Please enter your age: ");
i = input.nextInt(); // Getting an integer
System.out.println("Please enter your salary: ");
d = input.nextDouble(); // Getting a double
See how this differs: input.next();, i = input.nextInt();, d = input.nextDouble();
According to a String, int and a double varies the same way for the rest. Don't forget the import statement at the top of your code.
A simple example:
import java.util.Scanner;
public class Example
{
public static void main(String[] args)
{
int number1, number2, sum;
Scanner input = new Scanner(System.in);
System.out.println("Enter First multiple");
number1 = input.nextInt();
System.out.println("Enter second multiple");
number2 = input.nextInt();
sum = number1 * number2;
System.out.printf("The product of both number is %d", sum);
}
}
When the user enters his/her username, check for valid entry also.
java.util.Scanner input = new java.util.Scanner(System.in);
String userName;
final int validLength = 6; // This is the valid length of an user name
System.out.print("Please enter the username: ");
userName = input.nextLine();
while(userName.length() < validLength) {
// If the user enters less than validLength characters
// ask for entering again
System.out.println(
"\nUsername needs to be " + validLength + " character long");
System.out.print("\nPlease enter the username again: ");
userName = input.nextLine();
}
System.out.println("Username is: " + userName);
To read input:
Scanner scanner = new Scanner(System.in);
String input = scanner.nextLine();
To read input when you call a method with some arguments/parameters:
if (args.length != 2) {
System.err.println("Utilizare: java Grep <fisier> <cuvant>");
System.exit(1);
}
try {
grep(args[0], args[1]);
} catch (IOException e) {
System.out.println(e.getMessage());
}
import java.util.*;
class Ss
{
int id, salary;
String name;
void Ss(int id, int salary, String name)
{
this.id = id;
this.salary = salary;
this.name = name;
}
void display()
{
System.out.println("The id of employee:" + id);
System.out.println("The name of employye:" + name);
System.out.println("The salary of employee:" + salary);
}
}
class employee
{
public static void main(String args[])
{
Scanner sc = new Scanner(System.in);
Ss s = new Ss(sc.nextInt(), sc.nextInt(), sc.nextLine());
s.display();
}
}
Here is the complete class which performs the required operation:
import java.util.Scanner;
public class App {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
final int valid = 6;
Scanner one = new Scanner(System.in);
System.out.println("Enter your username: ");
String s = one.nextLine();
if (s.length() < valid) {
System.out.println("Enter a valid username");
System.out.println(
"User name must contain " + valid + " characters");
System.out.println("Enter again: ");
s = one.nextLine();
}
System.out.println("Username accepted: " + s);
Scanner two = new Scanner(System.in);
System.out.println("Enter your age: ");
int a = two.nextInt();
System.out.println("Age accepted: " + a);
Scanner three = new Scanner(System.in);
System.out.println("Enter your sex: ");
String sex = three.nextLine();
System.out.println("Sex accepted: " + sex);
}
}
There is a simple way to read from the console.
Please find the below code:
import java.util.Scanner;
public class ScannerDemo {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
// Reading of Integer
int number = sc.nextInt();
// Reading of String
String str = sc.next();
}
}
For a detailed understanding, please refer to the below documents.
Doc
Now let's talk about the detailed understanding of the Scanner class working:
public Scanner(InputStream source) {
this(new InputStreamReader(source), WHITESPACE_PATTERN);
}
This is the constructor for creating the Scanner instance.
Here we are passing the InputStream reference which is nothing but a System.In. Here it opens the InputStream Pipe for console input.
public InputStreamReader(InputStream in) {
super(in);
try {
sd = StreamDecoder.forInputStreamReader(in, this, (String)null); // ## Check lock object
}
catch (UnsupportedEncodingException e) {
// The default encoding should always be available
throw new Error(e);
}
}
By passing the System.in this code will opens the socket for reading from console.
You can flow this code:
Scanner obj= new Scanner(System.in);
String s = obj.nextLine();
You can use the Scanner class in Java
Scanner scan = new Scanner(System.in);
String s = scan.nextLine();
System.out.println("String: " + s);
import java.util.Scanner; // Import the Scanner class
class Main { // Main is the class name
public static void main(String[] args) {
Scanner myObj = new Scanner(System.in); // Create a Scanner object
System.out.println("Enter username");
String userName = myObj.nextLine(); // Read user input
System.out.println("Username is: " + userName); // Output user input
}
}
you have wrote
Scanner = input()
this is wrong method, you have to make an integer or a string, i would like to prefer string, and then give a string any name that can be i that can be n or anything else, remember that you are giving name to username you can also give name username also, and the code is
String username = sc.nextline();
System.our.println("the username is" + username);
I hope you understand now
As the title said I need to enter a string "Enter a number: " repeat itself after I've entered multiple values until I enter "DONE."
So for example it should look like this:
Enter a number:
4
Enter a number:
53
Enter a number:
DONE //closes program
This is a small part to a larger program and granted I know its simple, but I cant figure this out :[
What I'm guessing and been trying is a public static class with a toString method. But I can only get one "Enter a number: " printed once.
Enter a number:
4
53
DONE //closes program
Thanks in advance.
Some code I have for this part would be:
import java.util.Scanner;
public class EnterANumba
{
public static void main(String[] args)
{
while() //Stuck here
{
System.out.println("Enter a number:");
}
Scanner scanner = new Scanner(System.in);
String word=null;
while (scanner.hasNextLine())
{
word = scanner.nextLine();
if (word != null)
{
word = word.trim();
if (word.equalsIgnoreCase("done"))
{
break;
}
}
else
{
break;
}
}
I guess this following code snippet may help you.
public class Main {
public static void main(String[] args) {
Scanner s=new Scanner(System.in);
System.out.println("Enter a number:");
while(!(s.next().equalsIgnoreCase("DONE"))){
System.out.println("Enter a number:");
}
}
}
try asking for the 1st time and then make a loop where you validate the input and ask until the condition is met...
Example:
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter a number:");
while (!("done".equalsIgnoreCase(scanner.next()))) {
System.out.println("Enter a number:");
}
System.out.println("Enter a number:we are done....");
}
public static void main(String[] args) {
System.out.println("Input filename: ");
Scanner sc = new Scanner(System.in);
String input = sc.nextLine();
while (input.length() == 0){
System.out.println("Please enter names: ");
String names = sc.nextLine();
}
}
How do I make the program end when no more NAMES are entered?
while(input.length() == 0){ // use length() method
System.out.println("Please enter names: ");
String names = sc.nextLine(); //Same scanner but read names to enter into an array
}
}