Prompting a user for file name

Prompting a user for file name - java

I am attempting to learn how to prompt users to enter a file name, rather than predefining it, so that Java can go through with the Scanner and read through it. I have written a program that does what I need it to do, but only when the file in question is predefined.
I have looked around the site for duplicate questions, and found a few, but the scope in which it was asked was a bit more advanced than where I am. Can anyone offer me a bit of guidance on how to prompt a user to enter the file he/she wants, as opposed to predefining it (as code below is set to).
Note - This was written assuming the files read in had integers < 0 and > 0, hence why the min/max functions were done in the way they were...simply trying to teach myself one step at a time.
import java.io.*;
import java.util.*;
public class ProcessNumbers {
public static void main(String[] args) throws FileNotFoundException {
Scanner input = new Scanner(new File("inputdata.txt"));
int max = 0;
int min = 0;
int sum = 0;
int count = 0;
double average = 0;
System.out.println("Enter file name: "); //currently a println for ease of reading via Run
while (input.hasNext()) {
if (input.hasNextInt()) {
int number = input.nextInt();
sum += number;
count++;
average = (double) (sum) / count;
if (number > max) {
max = number;
}
if (number < min) {
min = number;
}
} else {
input.next();
}
}
System.out.println("Maximum = " + max);
System.out.println("Minimum = " + min);
System.out.println("Sum = " + sum);
System.out.println("Count = " + count);
System.out.println("average = " + average);
}
}

Try this:
System.out.println("Enter file name: ");
Scanner fileNameScanner = new Scanner( System.in );
String fileName = "";
if ( fileNameScanner .hasNext() ) {
fileName = fileNameScanner.next();
}
...
Using the fileName string, create a File object and use as per your requirements.

Easiest way would be to replace
new File("inputdata.txt")
with
new File(args[0])
This way the first command-line argument will be treated as a filename.

You can use Scanner to read a input from user (it doesn't only read from a File):
Scanner prompt = new Scanner(System.in);
System.out.print("Enter name of the file: ");
String name = prompt.next(); // enter "inputdata.txt"
Scanner input = new Scanner(new File(name));
// ...

Another approach would be to use the Console.
You substitute your scanner to read from a File returned from a new method:
Scanner input = new Scanner(getFileFromUser());
...
private static File getFileFromUser() {
Console c = System.console();
if (c == null) {
System.err.println("No console.");
System.exit(1);
}
String filePathname = c.readLine("Enter file pathname: ");
return new File(filePathname);
}
Also don't forget to close your scanner in the end of main method to avoid resource leak:
input.close();

Related

using the command line prompt in Java Eclipse [duplicate]

I attempted to create a calculator, but I can not get it to work because I don't know how to get user input.
How can I get the user input in Java?

One of the simplest ways is to use a Scanner object as follows:
import java.util.Scanner;
Scanner reader = new Scanner(System.in); // Reading from System.in
System.out.println("Enter a number: ");
int n = reader.nextInt(); // Scans the next token of the input as an int.
//once finished
reader.close();

You can use any of the following options based on the requirements.
Scanner class
import java.util.Scanner;
//...
Scanner scan = new Scanner(System.in);
String s = scan.next();
int i = scan.nextInt();
BufferedReader and InputStreamReader classes
import java.io.BufferedReader;
import java.io.InputStreamReader;
//...
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String s = br.readLine();
int i = Integer.parseInt(s);
DataInputStream class
import java.io.DataInputStream;
//...
DataInputStream dis = new DataInputStream(System.in);
int i = dis.readInt();
The readLine method from the DataInputStream class has been deprecated. To get String value, you should use the previous solution with BufferedReader
Console class
import java.io.Console;
//...
Console console = System.console();
String s = console.readLine();
int i = Integer.parseInt(console.readLine());
Apparently, this method does not work well in some IDEs.

You can use the Scanner class or the Console class
Console console = System.console();
String input = console.readLine("Enter input:");

You can get user input using BufferedReader.
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String accStr;
System.out.println("Enter your Account number: ");
accStr = br.readLine();
It will store a String value in accStr so you have to parse it to an int using Integer.parseInt.
int accInt = Integer.parseInt(accStr);

Here is how you can get the keyboard inputs:
Scanner scanner = new Scanner (System.in);
System.out.print("Enter your name");
String name = scanner.next(); // Get what the user types.

The best two options are BufferedReader and Scanner.
The most widely used method is Scanner and I personally prefer it because of its simplicity and easy implementation, as well as its powerful utility to parse text into primitive data.
Advantages of Using Scanner
Easy to use the Scanner class
Easy input of numbers (int, short, byte, float, long and double)
Exceptions are unchecked which is more convenient. It is up to the programmer to be civilized, and specify or catch the exceptions.
Is able to read lines, white spaces, and regex-delimited tokens
Advantages of BufferedInputStream
BufferedInputStream is about reading in blocks of data rather than a single byte at a time
Can read chars, char arrays, and lines
Throws checked exceptions
Fast performance
Synchronized (you cannot share Scanner between threads)
Overall each input method has different purposes.
If you are inputting large amount of data BufferedReader might be
better for you
If you are inputting lots of numbers Scanner does automatic parsing
which is very convenient
For more basic uses I would recommend the Scanner because it is easier to use and easier to write programs with. Here is a quick example of how to create a Scanner. I will provide a comprehensive example below of how to use the Scanner
Scanner scanner = new Scanner (System.in); // create scanner
System.out.print("Enter your name"); // prompt user
name = scanner.next(); // get user input
(For more info about BufferedReader see How to use a BufferedReader and see Reading lines of Chars)
java.util.Scanner
import java.util.InputMismatchException; // import the exception catching class
import java.util.Scanner; // import the scanner class
public class RunScanner {
// main method which will run your program
public static void main(String args[]) {
// create your new scanner
// Note: since scanner is opened to "System.in" closing it will close "System.in".
// Do not close scanner until you no longer want to use it at all.
Scanner scanner = new Scanner(System.in);
// PROMPT THE USER
// Note: when using scanner it is recommended to prompt the user with "System.out.print" or "System.out.println"
System.out.println("Please enter a number");
// use "try" to catch invalid inputs
try {
// get integer with "nextInt()"
int n = scanner.nextInt();
System.out.println("Please enter a decimal"); // PROMPT
// get decimal with "nextFloat()"
float f = scanner.nextFloat();
System.out.println("Please enter a word"); // PROMPT
// get single word with "next()"
String s = scanner.next();
// ---- Note: Scanner.nextInt() does not consume a nextLine character /n
// ---- In order to read a new line we first need to clear the current nextLine by reading it:
scanner.nextLine();
// ----
System.out.println("Please enter a line"); // PROMPT
// get line with "nextLine()"
String l = scanner.nextLine();
// do something with the input
System.out.println("The number entered was: " + n);
System.out.println("The decimal entered was: " + f);
System.out.println("The word entered was: " + s);
System.out.println("The line entered was: " + l);
}
catch (InputMismatchException e) {
System.out.println("\tInvalid input entered. Please enter the specified input");
}
scanner.close(); // close the scanner so it doesn't leak
}
}
Note: Other classes such as Console and DataInputStream are also viable alternatives.
Console has some powerful features such as ability to read passwords, however, is not available in all IDE's (such as Eclipse). The reason this occurs is because Eclipse runs your application as a background process and not as a top-level process with a system console. Here is a link to a useful example on how to implement the Console class.
DataInputStream is primarily used for reading input as a primitive datatype, from an underlying input stream, in a machine-independent way. DataInputStream is usually used for reading binary data. It also provides convenience methods for reading certain data types. For example, it has a method to read a UTF String which can contain any number of lines within them.
However, it is a more complicated class and harder to implement so not recommended for beginners. Here is a link to a useful example how to implement a DataInputStream.

You can make a simple program to ask for user's name and print what ever the reply use inputs.
Or ask user to enter two numbers and you can add, multiply, subtract, or divide those numbers and print the answers for user inputs just like a behavior of a calculator.
So there you need 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 same way for the rest. Don't forget the import statement at the top of your code.
Also see the blog post "Scanner class and getting User Inputs".

To read a line or a string, you can use a BufferedReader object combined with an InputStreamReader one as follows:
BufferedReader bufferReader = new BufferedReader(new InputStreamReader(System.in));
String inputLine = bufferReader.readLine();

Here, the program asks the user to enter a number. After that, the program prints the digits of the number and the sum of the digits.
import java.util.Scanner;
public class PrintNumber {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int num = 0;
int sum = 0;
System.out.println(
"Please enter a number to show its digits");
num = scan.nextInt();
System.out.println(
"Here are the digits and the sum of the digits");
while (num > 0) {
System.out.println("==>" + num % 10);
sum += num % 10;
num = num / 10;
}
System.out.println("Sum is " + sum);
}
}

Here is your program from the question using java.util.Scanner:
import java.util.Scanner;
public class Example {
public static void main(String[] args) {
int input = 0;
System.out.println("The super insano calculator");
System.out.println("enter the corrosponding number:");
Scanner reader3 = new Scanner(System.in);
System.out.println(
"1. Add | 2. Subtract | 3. Divide | 4. Multiply");
input = reader3.nextInt();
int a = 0, b = 0;
Scanner reader = new Scanner(System.in);
System.out.println("Enter the first number");
// get user input for a
a = reader.nextInt();
Scanner reader1 = new Scanner(System.in);
System.out.println("Enter the scend number");
// get user input for b
b = reader1.nextInt();
switch (input){
case 1: System.out.println(a + " + " + b + " = " + add(a, b));
break;
case 2: System.out.println(a + " - " + b + " = " + subtract(a, b));
break;
case 3: System.out.println(a + " / " + b + " = " + divide(a, b));
break;
case 4: System.out.println(a + " * " + b + " = " + multiply(a, b));
break;
default: System.out.println("your input is invalid!");
break;
}
}
static int add(int lhs, int rhs) { return lhs + rhs; }
static int subtract(int lhs, int rhs) { return lhs - rhs; }
static int divide(int lhs, int rhs) { return lhs / rhs; }
static int multiply(int lhs, int rhs) { return lhs * rhs; }
}

Scanner input = new Scanner(System.in);
String inputval = input.next();

Scanner input=new Scanner(System.in);
int integer=input.nextInt();
String string=input.next();
long longInteger=input.nextLong();

Just one extra detail. If you don't want to risk a memory/resource leak, you should close the scanner stream when you are finished:
myScanner.close();
Note that java 1.7 and later catch this as a compile warning (don't ask how I know that :-)

Here is a more developed version of the accepted answer that addresses two common needs:
Collecting user input repeatedly until an exit value has been entered
Dealing with invalid input values (non-integers in this example)
Code
package inputTest;
import java.util.Scanner;
import java.util.InputMismatchException;
public class InputTest {
public static void main(String args[]) {
Scanner reader = new Scanner(System.in);
System.out.println("Please enter integers. Type 0 to exit.");
boolean done = false;
while (!done) {
System.out.print("Enter an integer: ");
try {
int n = reader.nextInt();
if (n == 0) {
done = true;
}
else {
// do something with the input
System.out.println("\tThe number entered was: " + n);
}
}
catch (InputMismatchException e) {
System.out.println("\tInvalid input type (must be an integer)");
reader.nextLine(); // Clear invalid input from scanner buffer.
}
}
System.out.println("Exiting...");
reader.close();
}
}
Example
Please enter integers. Type 0 to exit.
Enter an integer: 12
The number entered was: 12
Enter an integer: -56
The number entered was: -56
Enter an integer: 4.2
Invalid input type (must be an integer)
Enter an integer: but i hate integers
Invalid input type (must be an integer)
Enter an integer: 3
The number entered was: 3
Enter an integer: 0
Exiting...
Note that without nextLine(), the bad input will trigger the same exception repeatedly in an infinite loop. You might want to use next() instead depending on the circumstance, but know that input like this has spaces will generate multiple exceptions.

import java.util.Scanner;
class Daytwo{
public static void main(String[] args){
System.out.println("HelloWorld");
Scanner reader = new Scanner(System.in);
System.out.println("Enter the number ");
int n = reader.nextInt();
System.out.println("You entered " + n);
}
}

Add throws IOException beside main(), then
DataInputStream input = new DataInputStream(System.in);
System.out.print("Enter your name");
String name = input.readLine();

It is very simple to get input in java, all you have to do is:
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 Myapplication{
public static void main(String[] args){
Scanner in = new Scanner(System.in);
int a;
System.out.println("enter:");
a = in.nextInt();
System.out.println("Number is= " + a);
}
}

You can get user input like this using a BufferedReader:
InputStreamReader inp = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(inp);
// you will need to import these things.
This is how you apply them
String name = br.readline();
So when the user types in his name into the console, "String name" will store that information.
If it is a number you want to store, the code will look like this:
int x = Integer.parseInt(br.readLine());
Hop this helps!

Can be something like this...
public static void main(String[] args) {
Scanner reader = new Scanner(System.in);
System.out.println("Enter a number: ");
int i = reader.nextInt();
for (int j = 0; j < i; j++)
System.out.println("I love java");
}

You can get the user input using Scanner. You can use the proper input validation using proper methods for different data types like next() for String or nextInt() for Integer.
import java.util.Scanner;
Scanner scanner = new Scanner(System.in);
//reads the input until it reaches the space
System.out.println("Enter a string: ");
String str = scanner.next();
System.out.println("str = " + str);
//reads until the end of line
String aLine = scanner.nextLine();
//reads the integer
System.out.println("Enter an integer num: ");
int num = scanner.nextInt();
System.out.println("num = " + num);
//reads the double value
System.out.println("Enter a double: ");
double aDouble = scanner.nextDouble();
System.out.println("double = " + aDouble);
//reads the float value, long value, boolean value, byte and short
double aFloat = scanner.nextFloat();
long aLong = scanner.nextLong();
boolean aBoolean = scanner.nextBoolean();
byte aByte = scanner.nextByte();
short aShort = scanner.nextShort();
scanner.close();

import java.util.Scanner;
public class Main {
public static void main(String[] args) {
System.out.println("Welcome to the best program in the world! ");
while (true) {
System.out.print("Enter a query: ");
Scanner scan = new Scanner(System.in);
String s = scan.nextLine();
if (s.equals("q")) {
System.out.println("The program is ending now ....");
break;
} else {
System.out.println("The program is running...");
}
}
}
}

This is a simple code that uses the System.in.read() function. This code just writes out whatever was typed. You can get rid of the while loop if you just want to take input once, and you could store answers in a character array if you so choose.
package main;
import java.io.IOException;
public class Root
{
public static void main(String[] args)
{
new Root();
}
public Root()
{
while(true)
{
try
{
for(int y = 0; y < System.in.available(); ++y)
{
System.out.print((char)System.in.read());
}
}
catch(IOException ex)
{
ex.printStackTrace(System.out);
break;
}
}
}
}

I like the following:
public String readLine(String tPromptString) {
byte[] tBuffer = new byte[256];
int tPos = 0;
System.out.print(tPromptString);
while(true) {
byte tNextByte = readByte();
if(tNextByte == 10) {
return new String(tBuffer, 0, tPos);
}
if(tNextByte != 13) {
tBuffer[tPos] = tNextByte;
++tPos;
}
}
}
and for example, I would do:
String name = this.readLine("What is your name?")

Keyboard entry using Scanner is possible, as others have posted. But in these highly graphic times it is pointless making a calculator without a graphical user interface (GUI).
In modern Java this means using a JavaFX drag-and-drop tool like Scene Builder to lay out a GUI that resembles a calculator's console.
Note that using Scene Builder is intuitively easy and demands no additional Java skill for its event handlers that what you already may have.
For user input, you should have a wide TextField at the top of the GUI console.
This is where the user enters the numbers that they want to perform functions on.
Below the TextField, you would have an array of function buttons doing basic (i.e. add/subtract/multiply/divide and memory/recall/clear) functions.
Once the GUI is lain out, you can then add the 'controller' references that link each button function to its Java implementation, e.g a call to method in your project's controller class.
This video is a bit old but still shows how easy Scene Builder is to use.

The most simple way to get user input would be to use Scanner. Here's an example of how it's supposed to be used:
import java.util.Scanner;
public class main {
public static void main(String[]args) {
Scanner sc=new Scanner(System.in);
int a;
String b;
System.out.println("Type an integer here: ");
a=sc.nextInt();
System.out.println("Type anything here:");
b=sc.nextLine();
The line of code import java.util.Scanner; tells the program that the programmer will be using user inputs in their code. Like it says, it imports the scanner utility. Scanner sc=new Scanner(System.in); tells the program to start the user inputs. After you do that, you must make a string or integer without a value, then put those in the line a=sc.nextInt(); or a=sc.nextLine();. This gives the variables the value of the user inputs. Then you can use it in your code. Hope this helps.

Using JOptionPane you can achieve it.
Int a =JOptionPane.showInputDialog(null,"Enter number:");

import java.util.Scanner;
public class userinput {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Name : ");
String name = input.next();
System.out.print("Last Name : ");
String lname = input.next();
System.out.print("Age : ");
byte age = input.nextByte();
System.out.println(" " );
System.out.println(" " );
System.out.println("Firt Name: " + name);
System.out.println("Last Name: " + lname);
System.out.println(" Age: " + age);
}
}

class ex1 {
public static void main(String args[]){
int a, b, c;
a = Integer.parseInt(args[0]);
b = Integer.parseInt(args[1]);
c = a + b;
System.out.println("c = " + c);
}
}
// Output
javac ex1.java
java ex1 10 20
c = 30

Why doesn't my program read my file that was created using the same program?

I'm trying to create a program that makes a file that randomly generates numbers and I want the program to read those numbers off of the file and analyze it. If the randomly generated number doesn't equal 0, the program should keep generating numbers, but if it does equal 0, then the program will stop. However, it seems that my program is not reading those numbers.
I tried putting the outFile.close(); and inFile.close(); in a couple different places to see if that would fix anything, but it seems that didn't work out. I tried tracing my code with pen and paper, but I couldn't find anything wrong. Perhaps it could be my placement of outFile.close(); and inFile.close();, but I couldn't find anything wrong with it.
import java.util.*;
import java.io.*;
public class squirrel {
public static void main(String[] args) throws IOException{
Scanner in = new Scanner(System.in);
PrintWriter outFile = new PrintWriter(new File("squirrel.txt"));
Scanner inFile = new Scanner(new File("squirrel.txt"));
Random rand = new Random();
int squirrelNum;
int foxSquirrel = 0;
int squirrelsSeen = 0;
int trials = 0;
System.out.println("Welcome to the Fox Squirrel Simulator\n");
System.out.println("How many trials should be simulated?");
System.out.println("Enter a value greater than 1000: ");
trials = in.nextInt();
while(trials <= 1000)
{
System.out.println("Please try again. Enter a value greater than 1000: ");
trials = in.nextInt();
}
for(int i = 0; i <= trials; i ++)
{
squirrelNum = rand.nextInt(10);
outFile.println(squirrelNum);
while(inFile.hasNextInt())
{
int token = inFile.nextInt();
while(token != 0)
{
squirrelsSeen ++;
}
if(token == 0)
{
foxSquirrel ++;
squirrelsSeen ++;
}
outFile.close();
}
System.out.println("squirrelsSeen: " + squirrelsSeen);
System.out.println("foxSquirrel: " + foxSquirrel);
}
inFile.close();
System.out.println("\nsimulating trials now... one moment please...\n");
System.out.println("The results!");
System.out.println("The average number of squirrels until spotting a Fox Squirrel at the city park is: " + (((double)foxSquirrel / squirrelsSeen) * 100));
}
}

And here is how it is done using Scanner.
File file = new File("squirrel.txt");
try {
Scanner sc = new Scanner(file);
while (sc.hasNextLine()) {
int i = sc.nextInt();
System.out.println(i);
}
sc.close();
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
And it is like you said. You put the .close() inside your while loop in your code. Try putting it outside.

new PrintWriter(new File("squirrel.txt")) immediately erases the file. From the documentation:
If the file exists then it will be truncated to zero size; otherwise, a new file will be created.
It is not possible to read and write the same file simultaneously. (Actually there are some cases were it’s possible, but they don’t apply here.)
Do not create your PrintWriter until you have finished reading from the file and have called inFile.close(). Or, write to a different file, then when you’re done, rename it to match the original file.

need help about reading numbers inside file

First I create a txt file (a.txt) -- DONE
create 10 random number from - to ( like from 5 -10 ) --DONE
I write this number in txt file --DONE
I want to check its written or not -- DONE
Now I need to find: how many number, biggest, smallest, sum of numbers
But I can not call that file and search in the file (a.txt). I am just sending last part. Other parts work. I need some help to understand. It is also inside another method. not main
Scanner keyboard = new Scanner(System.in);
boolean again = true;
int max = Integer.MIN_VALUE;
int min = Integer.MAX_VALUE;
int a = 0;
int count = 0;
System.out.println("Enter the filename to write into all analysis: ");
outputFileName = keyboard.nextLine();
File file2 = new File(outputFileName);
if (file2.exists()) {
System.out.println("The file " + outputFileName +
" already exists. Will re-write its content");
}
try {
PrintWriter yaz = new PrintWriter(file2);
// formulas here. created file a.txt need to search into that file biggest smallest and sum of numbers
yaz.println("Numeric data file name: " + inputFileName);
yaz.println("Number of integer: " + numLines);
yaz.println("The total of all integers in file: " + numLines); //fornow
yaz.println("The largest integer in the set: " + max);
yaz.println("The smallest integer in the set " + min);
yaz.close();
System.out.println("Data written to the file.");
} catch (Exception e) {
System.out.printf("ERROR reading from file %s!\n", inputFileName);
System.out.printf("ERROR Message: %s!\n", e.getMessage());
}

So you want a code to read a text file and give you the biggest, smallest and the average.
You can use Scanner class for that and use hasNextInt() to find integers
File f = new File("F:/some_text_file.txt"); // input your text file here
if(f.exists()){
try{
Scanner sc = new Scanner(f);
int max = Integer.MIN_VALUE;
int min = Integer.MAX_VALUE;
int temp=0, i=0;
double sum=0;
while(sc.hasNextInt()){
temp = sc.nextInt();
if(temp>max) max = temp;
if(temp<min) min =temp;
sum+=(double) temp;
i++;
}
System.out.println("average : " +sum/i);
System.out.println("large : "+max);
System.out.println("small :"+min);
sc.close();
}catch(Exception e){
e.printStackTrace();
}
}
See if this works

You need to read the file into memory. One way to do that is to move the text of the file into a String.
This post will help you: Reading a plain text file in Java
Here's the relevant code:
try(BufferedReader br = new BufferedReader(new FileReader("file.txt"))) {
StringBuilder sb = new StringBuilder();
String line = br.readLine();
while (line != null) {
sb.append(line);
sb.append(System.lineSeparator());
line = br.readLine();
}
String everything = sb.toString();
}

How do I add numbers from a list of user inputs? [duplicate]

This question already has an answer here:
java.lang.IllegalStateException: Scanner closed
(1 answer)
Closed 4 years ago.
I'm trying to write a program where it will tell you:
The number of integers in a list entered by the user at the command prompt
The sum of those integers.
But I'm having some trouble figuring out how to access those individual numbers. I've tried writing the while loop already, as well as the "if" statements.
Another issue I'm having is that when I try to run my program, I get this error message: Exception in thread "main" java.lang.IllegalStateException: Scanner closed.
NOTE: I'm very new to Java so a simpler solution that mainly uses scanners, next methods, and hasNext methods would be better!
import java.util.Scanner;
public class InputParser
{
public static void main(String[] args)
{
Scanner scanner = new Scanner(System.in);
System.out.print("How many values do you want to parse?: ");
int numValues = scanner.nextInt();
System.out.println("Please enter " + numValues + " values: ");
while(scanner.hasNextLine())
{
if(scanner.hasNext())
{
if(scanner.hasNextInt())
{
int sum;
System.out.println("The sum of your values is: " + sum + ".");
}
}
scanner.close();
}
}
}

Your code should be like:
Scanner scanner = new Scanner(System.in);
System.out.print("How many values do you want to parse?: ");
int numValues = scanner.nextInt();
int[] values = new int(numValues);
int sum = 0,i=0;
while(i<numValues)
{ i++;
System.out.print("Enter "+ i+" number : ");
values[i-1] = scanner.nextInt();
sum+= values[i-1];
}
System.out.println("Sum is : "+sum);
scanner.close();
Haven't really consider error handling.

I don't understand why you would ask the user how many numbers they want to sum ahead of time. Basically, your code can be simplified and handle an arbitrary number of numbers. It's also a really bad idea to call close() on a Scanner wrapping System.in (Because you can't re-open it, and if you extract it into a method you will create a hard to debug and find issue). Anyway, you could do something like,
Scanner scanner = new Scanner(System.in);
// System.out.print("How many values do you want to parse?: ");
// int numValues = scanner.nextInt();
System.out.println("Please enter values to sum (type quit to stop)");
int sum = 0; // <-- start at 0.
int count = 0;
while (scanner.hasNext()) {
if (scanner.hasNextInt()) {
count++;
sum += scanner.nextInt();
} else {
String str = scanner.next();
if (str.equalsIgnoreCase("quit")) {
break; // <-- end the loop.
}
System.out.printf("The value '%s' is not an int (quit to stop).%n", str);
}
}
System.out.printf("The sum of your %d values is %d.%n", count, sum);
// scanner.close(); // <-- Really Bad Idea
Edit Based on your comment,
Scanner scanner = new Scanner(System.in);
System.out.println("Please enter values to sum (type quit to stop)");
while (scanner.hasNextLine()) {
String str = scanner.nextLine();
str = (str != null) ? str.trim() : "";
if (str.equalsIgnoreCase("quit")) {
break; // <-- end the loop.
} else if (str.length() == 0) {
continue;
}
int sum = 0; // <-- start at 0.
int count = 0;
Scanner scan2 = new Scanner(str);
while (scan2.hasNextInt()) {
count++;
sum += scan2.nextInt();
}
System.out.printf("The sum of your %d values is %d.%n", count, sum);
}

How do I get the list of numbers off of a file that the user inputs in Java?

I am using Java eclipse and I would like to have the user input the filename to retrieve a list of scores from the file. My goal is to take the average of those numbers. What line of code do I need just to get the user to input a file name and for the program to take those numbers so that I can compute with them? Currently I can have the user input scores, But I need to get the numbers from the file instead. I have visited numerous resources on this site. Here are a few:
BufferedReader, Error finding file, Getting a list from a file
package Average;
/**An average of scores*/
import java.util.Scanner;
public class Average2 {
public static void main(String[] args) {
int grade = 0;
int students = 0;
float total = 0;
double average = 0;
Scanner input = new Scanner(System.in);
System.out.println("Enter number of students: ");
students = input.nextInt();
if (students <= 10) {
System.out.println("Enter the grades of the students: ");
for(int i = 0; i < students; i++) {
do {
grade = input.nextInt();
} while(grade < 0 || grade > 100);
total += grade;
}
average = (total/students);
int median = ((82+84)/2);
System.out.println("The average is " + average);
System.out.println("The mean is " + median);
}
}
}
Update since above post!
package trials;
import java.io.File;
import java.io.IOException;
import java.util.Scanner;
public class trials2 {
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
// Create new Scanner object to read from the keyboard
Scanner in = new Scanner(System.in);
// Grab the name of the file
System.out.println("Enter filename: ");
String fileName = in.next();
// Access the file
Scanner fileToRead = new Scanner(new File(fileName));
// While there is still stuff in the file...
double sum = 0;
while (fileToRead.hasNext()) {
if (fileToRead.hasNextDouble()) {
sum += fileToRead.nextDouble();
} else {
fileToRead.next();
}
}
{
fileToRead.close();
}
System.out.println(sum);
}
}
The results I get from this:
Enter filename:
esp.txt <--entered by me
501.0

Given that you want to find the average of numbers in a file, you could do something like this:
// Create new Scanner object to read from the keyboard
Scanner in = new Scanner(System.in);
// Grab the name of the file
System.out.println("Enter filename: ");
String fileName = in.next();
// Access the file
Scanner fileToRead = new Scanner(new File(fileName));
// Initialize our relevant counters
double sum = 0.0;
int numStudents = 0;
// While there is still stuff in the file...
while (fileToRead.hasNext()) {
// Is this next line consisting of just a number?
if (fileToRead.hasNextDouble()) {
// If it is, accumulate
sum += fileToRead.nextDouble();
numStudents++;
}
else { // Else, just skip to the next line
fileToRead.next();
}
}
// Close the file when finished
fileToRead.close();
// Print the average:
System.out.println("The average mark is: " + (sum / numStudents));
This code will create a new Scanner object that will read input from your keyboard. Once it does that, you type in the file name, and it gets access to this file by opening another Scanner object. After that, we initialize some counters to help us calculate the average. These are sum, which will add up all of the marks we encounter and numStudents, which keeps track of how many students there are in the file.
The while loop will keep looping through each line of this file until it reaches the end. What is important is that you check to see whether or not the line you are reading in next consists of a single number (double). If it is, then add this to our sum. If it isn't, skip to the next line.
Once you're finished, close the file, then display the average by taking the sum and dividing by the total number of students we have encountered when reading the numbers in the file.
Just took a look at your profile and your profile message. You have a long road ahead of you. Good luck!

Look at the Java tutorial on Scanning: http://docs.oracle.com/javase/tutorial/essential/io/scanning.html, particularly the ScanSum example. It shows how to scan double values from a text file and add them. You should be able to modify this example for your project.

Scanner userInput = new Scanner(System.in);
System.out.println("ENter filename");
String fileName = userInput.next();
Scanner fileScan = new Scanner(new File(fileName));
then use scanner methods to process lines or string tokens you are interested in.

Develop Reference

Java is a programming language and computing platform first released by Sun Microsystems in 1995.

Prompting a user for file name - java

Try this: System.out.println("Enter file name: "); Scanner fileNameScanner = new Scanner( System.in ); String fileName = ""; if ( fileNameScanner .hasNext() ) { fileName = fileNameScanner.next(); } ... Using the fileName string, create a File object and use as per your requirements.

Easiest way would be to replace new File("inputdata.txt") with new File(args[0]) This way the first command-line argument will be treated as a filename.

You can use Scanner to read a input from user (it doesn't only read from a File): Scanner prompt = new Scanner(System.in); System.out.print("Enter name of the file: "); String name = prompt.next(); // enter "inputdata.txt" Scanner input = new Scanner(new File(name)); // ...

Related

using the command line prompt in Java Eclipse [duplicate]

Why doesn't my program read my file that was created using the same program?

need help about reading numbers inside file

How do I add numbers from a list of user inputs? [duplicate]

How do I get the list of numbers off of a file that the user inputs in Java?

Categories

Resources