I implemented a java program with some methods. Next I created a main class which will call the related method by entering a word.
for example:
Enter {A|B|C|D|E} to call method. A=method one B = method two...etc
A<--this is the user input
Enter Number:<--the first Scanner input of method A
123<--Input 1
Enter words:<-- the second Scanner input of method A
ABC<--Input 2
123ABC<--The output method A
Enter {A|B|C|D|E} to call method. A=method one B = method two...etc
B<--this is the user input
Enter Number 1:<--the first Scanner input of method B
100<--Input 1
Enter Number 2:<-- the second Scanner input of method B
50<--Input 2
150<--The output method B
Code of Method A {
String output;
private static Scanner keyboard = new Scanner(System.in);
System.out.println("Enter Number:");
String no = keyboard.nextLine();
System.out.println("Enter Words:");
String words = keyboard.nextLine();
//do something...
System.out.println(output);
}
Code of Main class{
private static Scanner keyboard = new Scanner(System.in);
public static void main(String[] args){
Main main = new Main();
main.run();
}
public void run() {
boolean running = true;
while (running) {
displayMenu();
String command = keyboard.nextLine();
String[] parts = command.split("^");
if ("A".equalsIgnoreCase(command)) {
//call method A
} else if ("B".equalsIgnoreCase(command)) {
//call method B
} else if....etc
System.out.println();
}
what I want is input
A123 , ABCB100,50 at once
then the system will print the output of method A (123ABC) and B (150) for me.
What I want is input A into "keyboard", input 123 into "no" and input ABC into "words" at once
How can I do it?
As long as your don't close your Scanner (or its underlying input stream), the yet-to-read tokens will remain accessible for later use : read two lines (or 4 tokens - the comma is one) and "B\n100,50" will remain.
If you're asking how to provide this kind of input, it depends on your invokation method. If executed from bash, I'd use the following :
echo """A
123 , ABC
B
100,50""" | java ...
If you're asking how to dynamically invoke a method from its name, check the reflection API. Oracle's tutorial is a good resource in my opinion, here's a link to its section on retrieving and invoking methods.
There are 2 ways to do that.
First:
Instead of giving input directly in the console, first write all the data input somewhere and just copy it and paste it in the console.
Second:
You can use hasNexLine() and send EOF through keyboard by pressing ctrl+d.
Code:
public static void main(String[] args)
{
Scanner s = new Scanner(System.in);
StringBuilder sb = new StringBuilder();
while(s.hasNextLine())
{
sb.append(s.nextLine());
}
System.out.println(sb.toString());
}
Provide all your input and press ctrl+d to stop taking input.
Related
I am working on creating a program for my course, in which I am required to divide the string: This;is;the;first;line;;This;is;the;second;line!;;;;Done!;;.
In the requirements, I need to read a single semicolon as a space, and a double semicolon as a new line. How do I create a regular expression in the useDelimiter() method that allows me to parse through and differentiate between both ; and ;;? Thank you!
Assignment Excerpt:
Instead of hard-coding the string, this time you will read it from the console. Study the useDelimiter() method and use it to set the delimiter for the scanner input. This time allow either colons or semicolons as the delimiters. One might prefer to use the String Tokenizer here, but don’t -- use the Scanner’s useDelimiter() method to set the delimiter in the Scanner and process each token as it comes.
import java.util.Scanner;
public class Hw3p2 {
public static void main(String[] args) {
// Initializes scanner class.
Scanner input = new Scanner(System.in);
// Prompts user for input.
System.out.println("Enter the string you wish to filter & parse: ");
// Reads user input.
String filterString = input.nextLine();
// Initiates new scanner reading the user inputted string.
Scanner a = new Scanner(filterString);
a.useDelimiter(";|;;");
System.out.printf("\n");
// Loop that parses through string while there are more tokens.
while(a.hasNext()) {
System.out.print(a.next());
}
}
}
The Expected output is to be:
You may use this code:
public class Hw3p2 {
public static void main(String[] args) {
// Initializes scanner class.
Scanner input = new Scanner(System.in).useDelimiter(";;");
// Prompts user for input.
System.out.print("Enter the string you wish to filter & parse: ");
// Reads user input.
while(input.hasNext()) {
String filterString = input.next();
//System.err.println("filterString: " + filterString);
// Initiates new scanner reading the user inputted string.
Scanner a = new Scanner(filterString).useDelimiter(";");
// Loop that parses through string while there are more tokens.
while(a.hasNext()) {
System.out.print(a.next() + " ");
}
System.out.println();
a.close();
}
input.close();
}
}
Output:
Enter the string you wish to filter & parse: This;is;the;first;line;;This;is;the;second;line!;;;;Done!;;
This is the first line
This is the second line!
Done!
Note use of outer scanner with delimiter ;; and an inner one with ;.
I'm writing sort of main practice project, where I can just continually add classes that do completely different fun things. For example, I have a CoinFlipperCmd and a poker PotOddsCmd, and the code currently works fine, but I want to be able to repeatedly enter commands without having to rerun the program. Example console currently:
FLIP 10 // coinflips 10 times and notes the outcome
You flipped 5 heads and 5 tails
After this, the code will exit, but I want to be able to keep entering commands. Like so:
FLIP 5
You flipped 4 heads and 1 tails
FLIP 6
You flipped 3 heads and 3 tails
POTODDS 0.5 1
You have pot odds of 2:1
I'm using a scanner for input
import java.util.Scanner; // Import the Scanner class
public class Main {
public static void main(String[] args) {
InputScanner();
}
private static void InputScanner() {
Scanner myObj = new Scanner(System.in); // Create a Scanner object
System.out.println("Enter command");
String command = myObj.nextLine(); // Read user input
ParseAndDirect(command);
}
private static void ParseAndDirect(String command) {
String[] commandSplit = command.split(" ", 2);
String usercommand = commandSplit[0];
if (usercommand.equals("FLIP")){
CoinFlipperCmd.CoinFlipperCmd(commandSplit[1]);
} else if (usercommand.equals("POTODDS")){
PotOddsCmd.PotOddsCmd(commandSplit[1]);
} else System.out.println("Invalid Command");
}
}
You need to put the input part inside a loop e.g.
private static void InputScanner() {
Scanner myObj = new Scanner(System.in); // Create a Scanner object
String command;
do {
System.out.print("Enter command (q to quit): ");
command = myObj.nextLine(); // Read user input
if (!command.equalsIgnoreCase("q")) {
ParseAndDirect(command);
}
} while (!command.equalsIgnoreCase("q"));
}
Another way of using the loop can be as follows:
private static void InputScanner() {
Scanner myObj = new Scanner(System.in); // Create a Scanner object
String command;
while(true)
System.out.print("Enter command (q to quit): ");
command = myObj.nextLine(); // Read user input
if (command.equalsIgnoreCase("q")) {
break;
}
ParseAndDirect(command);
}
}
On a side note (because it won't have any impact on the execution of the program), you should always follow Java naming conventions e.g the method, ParseAndDirect should be named as parseAndDirect and InputScanner should be named as inputScanner.
Apart from allowing the user to repeatedly enter commands, I think you should also allow some way to quit the program (besides having to kill it via the operating system :-) In the below code, I have arbitrarily used the word quit as the way to exit the loop. Feel free to use a different string.
Scanner myObj = new Scanner(System.in);
String command = "";
while (!"quit".equalsIgnoreCase(command)) {
System.out.println("Enter command");
if (!"quit".equalsIgnoreCase(command)) {
ParseAndDirect(command);
}
}
By the way, according to java naming conventions the method name should be parseAndDirect, i.e. it should start with a lowercase letter.
I have a Test class that creates a Scanner and reads a user's input. I want to recognize when a user pressed Enter, so I check if the next symbol of the input equals to lineSeparator. However, even though I do press Enter it doesn't get recognized as such.
public class Test {
public static void main(String[] args) {
Scanner reader = new Scanner(System.in);
if (reader.next().equals(System.lineSeparator())) {
System.out.println("finished");
}
/but at the same time, this one works as expected:
String temp = "dog" + System.lineSeparator() + "cat";
System.out.println(temp);
}
}
At the same time when I construct a string using lineSeparator, it works fine, adding a new line as expected.
What is wrong here and how to recognize if a user pressed Enter?
change your code to use hasNextLine() to check if nextline exists and then nextLine() to read the nextLine. Something like this
public static void main(String[] args) {
Scanner reader = new Scanner(System.in);
while (reader.hasNextLine()) {
System.out.println(reader.nextLine());
}
System.out.println("finished");
}
This program goes in an infinite loop in while cycle. Please, can someone tell me why?
import java.util.Scanner;
public class program {
public static void main(String[] pars) {
System.out.println("Insert something.");
Scanner read = new Scanner(System.in);
String s = "";
while(read.hasNext()) {
System.out.println(read.next());
}
System.out.println("End of program");
}
}
Read the Javadoc of Scanner#hasNext():
Returns true if this scanner has another token in its input. This method may block while waiting for input to scan. The scanner does not advance past any input.
Hence the while loop will always be executed in your case, each time waiting for input from the user. Since the Scanner is linked to System.in, the input stream will always block until the user inputs a string and hasNext() will always return true, unless the user signals the end of file (e.g. through the Ctrl+z combination on Windows). Scanner#hasNext() is more convenient when reading from files where the input size is known and the end of the file marks the end of the stream.
One way to end the loop here is to add a condition on the input:
while (read.hasNext()) {
s = read.next();
if(s.equals("quit")) {
break;
}
System.out.println(s);
}
P.S.: It is more conventional to name classes starting with an uppercase letter.
The problem is this line:
while(read.hasNext()) {
If you use System.in as a stream provided by the user, it will - if no such input is available - as #manouti says, block and wait for input. But even if you provide input, it will keep waiting. The system has no means to detect whether the user wants to provide additional input in the future.
It will only stop, if the Stream ends. This can be under two conditions:
The end of the file (in case of I/O redirection like java -jar program.jar < input.dat; or
The user marks the end of a stream, in most shells with Ctrl+D. This marks the end-of-stream.
An alternative is to provide some kind of stop directive. Something like "END". Thus:
while(read.hasNext()) {
String nx = read.next();
if(nx.equals("END")) {
break;
}
System.out.println(nx);
}
Just remove while loop
public static void main(String[] pars) {
System.out.println("Insert something.");
Scanner read = new Scanner(System.in);
String s = "";
System.out.println(read.next());
System.out.println("End of program");
}
Or if u want display certain no.of string then mention condition properly.
public static void main(String[] pars) {
System.out.println("Insert something.");
Scanner read = new Scanner(System.in);
String s = "";
int i=0;
while(i<5) {
System.out.println(read.next());
i++;
}
System.out.println("End of program");
}
I need help doing the following:
receiving input using Scanner class (I got this)
taking input from scanner and making it a String
use replaceAll to remove numbers 0-9 from user input.
The below code is what I have so far but it is only returning user input and not removing numbers:
public static void main(String[] args) {
Scanner firstname = new Scanner(System.in);
System.out.println("Please enter your first name:");
String firstname1 = firstname.next();
firstname1.replaceAll("[^0-9]","");
System.out.println(firstname1);
Updated Code. Thank you Hovercraft. I am now investigating how to retrieve all alpha characters as with the code below, I am only getting back the letters prior to the numeric values entered by the user:
import java.util.Scanner;
public class Assignment2_A {
public static void main(String[] args) {
Scanner firstname = new Scanner(System.in);
System.out.println("Please enter your first name:");
String firstname1 = firstname.next();
firstname1 = firstname1.replaceAll("[^A-Z]","");
System.out.println(firstname1);
String input = yourScannerObject.nextLine ();
where "yourScannerObject" is the name you give your scanner.
What method did you use to scan? is it {scanner object name}.next() ?
if so you have got a string and all that you have to do is create some string, and save the input to it, e.g.:
String str="";
str = {scanner object name}.next();
before using anything in java, I would advise you to read the API :
http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Scanner.html#next()
receiving input using Scanner class (I got this)
taking input from scanner and making it a String
use replaceAll to remove numbers 0-9 from user input.
Here's an example:
String in;
Scanner scan = new Scanner("4r1e235153a6d 6321414t435hi4s 4524str43i5n5g");
System.out.println(in = (scan.nextLine().replaceAll("[0-9]", ""))); // use .next() for space or tab
Output:
read this string
The problem in your code is the regex "[^A-Z]" is set to remove all non-alphabet capital characters. This means you remove all lower case as well. You could say "[^a-zA-Z]", but then you're also removing special characters.