How to read input with multiple lines in Java

Question

Our professor is making us do some basic programming with Java, he gave a website and everything to register and submit our questions, for today I need to do this one example I feel like I'm on the right track but I just can't figure out the rest. Here is the actual question:

**Sample Input:**
10 12
10 14
100 200

**Sample Output:**
2
4
100

And here is what I've got so far :

public class Practice {

    public static int calculateAnswer(String a, String b) {
        return (Integer.parseInt(b) - Integer.parseInt(a));
    }

    public static void main(String[] args) {
        System.out.println(calculateAnswer(args[0], args[1]));
    }
}

Now I always get the answer 2 because I'm reading the single line, how can I take all lines into account? thank you

For some strange reason every time I want to execute I get this error:

C:\sonic>java Practice.class 10 12
Exception in thread "main" java.lang.NoClassDefFoundError: Fact
Caused by: java.lang.ClassNotFoundException: Fact.class
        at java.net.URLClassLoader$1.run(URLClassLoader.java:20
        at java.security.AccessController.doPrivileged(Native M
        at java.net.URLClassLoader.findClass(URLClassLoader.jav
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248
Could not find the main class: Practice.class.  Program will exit.

Whatever version of answer I use I get this error, what do I do ?

However if I run it in eclipse Run as > Run Configuration -> Program arguments

10 12
10 14
100 200

I get no output

EDIT

I have made some progress, at first I was getting the compilation error, then runtime error and now I get wrong answer, so can anybody help me what is wrong with this:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;

public class Practice {

    public static BigInteger calculateAnswer(String a, String b) {
        BigInteger ab = new BigInteger(a);
        BigInteger bc = new BigInteger(b);
        return bc.subtract(ab);
    }

    public static void main(String[] args) throws IOException {
        BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in)); 
        String line; 

        while ((line = stdin.readLine()) != null && line.length()!= 0) { 
            String[] input = line.split(" "); 
            if (input.length == 2) { 
                System.out.println(calculateAnswer(input[0], input[1])); 
            } 
        } 
    }
}

Did your professor specify how he expects you to get the input into your program? From the command line, read from a file, typed into the program as it's running? — Nate
– Nate, Commented Feb 19, 2010 at 14:37
@Nate umm he gave us a website uva.onlinejudge.org so we register there give him our usernames, and he expects us to solve a problem each day which is a good thing.. and since I can't get this example to work on my computer there is no purpose of sumbitting it. The problem I'm trying to solve is 10055 - Hashmat the Brave Warrior acm.uva.es/p/v100/10055.html — Gandalf StormCrow
– Gandalf StormCrow, Commented Feb 19, 2010 at 14:41

Gandalf StormCrow · Accepted Answer · 2010-02-19 15:58:55Z

27

I finally got it, submited it 13 times rejected for whatever reasons, 14th "the judge" accepted my answer, here it is :

import java.io.BufferedInputStream;
import java.util.Scanner;

public class HashmatWarrior {

    public static void main(String args[]) {
        Scanner stdin = new Scanner(new BufferedInputStream(System.in));
        while (stdin.hasNext()) {
            System.out.println(Math.abs(stdin.nextLong() - stdin.nextLong()));
        }
    }
}

answered Feb 19, 2010 at 15:58

Gandalf StormCrow

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2 Comments

Arindam Paul Over a year ago

Using Scanner class is the exact thing I was looking for, thanks a lot

Thinker Over a year ago

br = new BufferedReader(new InputStreamReader(new FileInputStream("/home/prashank/Desktop/input.txt"))); this could also save the day. I used it often for heavy data.

Péter Török · Accepted Answer · 2010-02-19 14:01:14Z

9

Use BufferedReader, you can make it read from standard input like this:

BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
String line;

while ((line = stdin.readLine()) != null && line.length()!= 0) {
    String[] input = line.split(" ");
    if (input.length == 2) {
        System.out.println(calculateAnswer(input[0], input[1]));
    }
}

answered Feb 19, 2010 at 14:01

Péter Török

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Comments

trashgod · Accepted Answer · 2010-02-19 14:01:41Z

2

A lot of student exercises use Scanner because it has a variety of methods to parse numbers. I usually just start with an idiomatic line-oriented filter:

import java.io.*;

public class FilterLine {

    public static void main(String[] args) throws IOException {
        BufferedReader in = new BufferedReader(
            new InputStreamReader(System.in));
        String s;

        while ((s = in.readLine()) != null) {
            System.out.println(s);
        }
    }
}

answered Feb 19, 2010 at 14:01

trashgod

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Comments

Raghuveer Reddy · Accepted Answer · 2017-05-03 07:59:05Z

2

 public class Sol {

   public static void main(String[] args) {

   Scanner sc = new Scanner(System.in); 

   while(sc.hasNextLine()){

   System.out.println(sc.nextLine());

  }
 }
}

edited May 3, 2017 at 7:59

answered May 3, 2017 at 6:36

Raghuveer Reddy

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1 Comment

LoïcR Over a year ago

Adding a bit if explanation with your code would be nice.

Hank Gay · Accepted Answer · 2010-02-19 13:55:53Z

1

Look into BufferedReader. If that isn't general/high-level enough, I recommend reading the I/O tutorial.

answered Feb 19, 2010 at 13:55

Hank Gay

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2 Comments

Gandalf StormCrow Over a year ago

@Hank Gay its not from a file, it would be easy to do that its from console arguments

Buhake Sindi Over a year ago

@Gandalf, you can do this with BufferedReader. BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));

Nate · Accepted Answer · 2010-02-19 14:41:08Z

0

The problem you're having running from the command line is that you don't put ".class" after your class file.

java Practice 10 12

should work - as long as you're somewhere java can find the .class file.

Classpath issues are a whole 'nother story. If java still complains that it can't find your class, go to the same directory as your .class file (and it doesn't appear you're using packages...) and try -

java -cp . Practice 10 12

answered Feb 19, 2010 at 14:41

Nate

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1 Comment

Nate Over a year ago

Is Practice.class in the same directory you're executing java -cp . Practice 10 12 from?

Ashutosh K Singh · Accepted Answer · 2018-07-03 15:54:42Z

0

The easilest way is

import java.util.*;

public class Stdio4 {

public static void main(String[] args) {
    int a=0;
    int arr[] = new int[3];
    Scanner scan = new Scanner(System.in);
    for(int i=0;i<3;i++)
    { 
         a = scan.nextInt();  //Takes input from separate lines
         arr[i]=a;


    }
    for(int i=0;i<3;i++)
    { 
         System.out.println(arr[i]);   //outputs in separate lines also
    }

}

}

answered Jul 3, 2018 at 15:54

Ashutosh K Singh

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1 Comment

Ralf Stubner Over a year ago

While this code snippet may solve the question, including an explanation really helps to improve the quality of your post. Remember that you are answering the question for readers in the future, and those people might not know the reasons for your code suggestion.

Nasar · Accepted Answer · 2019-03-30 17:24:01Z

0

This is good for taking multiple line input

import java.util.Scanner;
public class JavaApp {
    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        String line;
        while(true){
            line = scanner.nextLine();
            System.out.println(line);
            if(line.equals("")){
                break;
            }
        }
    }  
}

answered Mar 30, 2019 at 17:24

Nasar

761 silver badge8 bronze badges

Comments

thkala · Accepted Answer · 2012-01-06 17:56:36Z

-1

import java.util.*;
import java.io.*;

public class Main {
    public static void main(String arg[])throws IOException{
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);
        StringTokenizer st;
        String entrada = "";

        long x=0, y=0;

        while((entrada = br.readLine())!=null){
            st = new StringTokenizer(entrada," ");

            while(st.hasMoreTokens()){
                x = Long.parseLong(st.nextToken());
                y = Long.parseLong(st.nextToken());
            }

            System.out.println(x>y ?(x-y)+"":(y-x)+"");
        }
    }
}

This solution is a bit more efficient than the one above because it takes up the 2.128 and this takes 1.308 seconds to solve the problem.

edited Jan 6, 2012 at 17:56

thkala

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answered Apr 10, 2010 at 0:59

Executor100

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1 Comment

Kuchi Over a year ago

Since this is a Educational exercise there is no need to do performance improvement. Code readability > performance!

Baby Groot · Accepted Answer · 2013-04-19 04:54:23Z

package pac001;

import javax.swing.JFrame;
import javax.swing.JOptionPane;

public class Entry_box{



    public static final String[] relationship = {"Marrid", "Unmarried"};


    public static void main(String[] args)
    {
         //TAKING USER ID NUMBER
            int a = Integer.parseInt(JOptionPane.showInputDialog("Enter ID no: "));
        // TAKING INPUT FOR RELATIONSHIP
        JFrame frame = new JFrame("Input Dialog Example #3");
        String Relationship =   (String) JOptionPane.showInputDialog(frame,"Select Your Relationship","Married",
                                JOptionPane.QUESTION_MESSAGE, null, relationship,relationship[0]);



        //PRINTING THE ID NUMBER
        System.out.println("ID no: "+a);
        // PRINTING RESULT FOR RELATIONSHIP INPUT
          System.out.printf("Mariitual Status: %s\n", Relationship);

        }
}

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