Develop Reference

Java Scanner Class ( System.in)

I have the below code that is not reading or infinitely looping when a user inputs text using System.in. If I hard code the text into the Scanner variable it works fine so I am not sure what is wrong with the System.in portion of this code. Any help is appreciated.
import java.util.Scanner; // needed to use the Scanner class
public class HW2 {
static Scanner in = new Scanner(System.in);
public static void main(String [] args) {
System.out.println("Enter your line here");
int the =0;
int and =0;
int is = 0;
int was =0;
int noword =0;
while (in.hasNext()){
String word = in.next();
if (word.equals("the")){
the++;
}
else if( word.equals("and")){
and ++;
}
else if (word.equals("is")){
is++;
}
else if (word.equals("was")){
was++;
}
else noword++;
}
System.out.println("The number of occurrences of the was"+ the);
System.out.println("The number of occurrences of and was"+ and);
System.out.println("The number of occurrences of is was"+ is);
System.out.println("The number of occurrences of was was"+ was);
}
}

As has been mentioned, a Scanner attached to System.in will block while looking for more input. One way to approach this would be to read a single line in from the scanner, tokenize it, and then loop through the words that way. That would look something like this:
//...
String line = in.nextLine(); // Scanner will block waiting for user to hit enter
for (String word : line.split(" ")){
if (word.equals("the")) {
the++;
}
//...
You can always substitute one loop structure (for, while, do-while) for another. They all do the same thing, just with different syntax to make one a bit simpler to use than others depending on the circumstances. So if you want to use a while loop, you can do something like this:
// ...
String line = in.nextLine();
String[] tokens = line.split(" ");
int i = 0;
while (i < tokens.length){
String word = tokens[i];
if (word.equals("the")) {
the++;
}
// ...
i++;
} // end of the while loop
However, I'm of the opinion that a for loop is cleaner in the case of looping over a known set of data. While loops are better when you have an unknown dataset, but a known exit condition.

As System.in is always available while the program is running unless you close it. It will never exit the while loop. So you could add else if (word.equals("exit")) { break; }. This way, whenever you type 'exit' it will close the while loop and execute the code AFTER the while loop.

Depends, do you want to just read 1 line of text and then count the words individually?
Because is you want only one line you could take the input string using the Scanner library and split the string into individual words and apply the if-statement then. Something like:
public static void main(String [] args) {
System.out.println("Enter your line here");
int the =0;
int and =0;
int is = 0;
int was =0;
int noword =0;
String input = in.nextLine();
String words[] = input.split(" ");
for (String s : words) {
if (s.equals("the")){
the++;
} else if( s.equals("and")){
and++;
} else if (s.equals("is")){
is++;
} else if (s.equals("was")){
was++;
} else {
noword++;
}
}
System.out.println("The number of occurrences of the was: "+ the);
System.out.println("The number of occurrences of and was: "+ and);
System.out.println("The number of occurrences of is was: "+ is);
System.out.println("The number of occurrences of was was: "+ was);
}
This way you won't need a while loop at all. So it's more processor and memory efficient.

How would I go about using an integer delimiter? (Java)

So I am trying to read a file using a scanner. This file contains data where there are two towns, and the distance between them follows them on each line. So like this:
Ebor,Guyra,90
I am trying to get each town individual, allowing for duplicates. This is what I have so far:
// Create scanner for file for data
Scanner scanner = new Scanner(new File(file)).useDelimiter("(\\p{javaWhitespace}|\\.|,)+");
// First, count total number of elements in data set
int dataCount = 0;
while(scanner.hasNext())
{
System.out.print(scanner.next());
System.out.println();
dataCount++;
}
Right now, the program prints out each piece of information, whether it is a town name, or an integer value. Like so:
Ebor
Guyra
90
How can I make it so I have an output like this for each line:
Ebor
Guyra
Thank you!

Assuming well-formed input, just modify the loop as:
while(scanner.hasNext())
{
System.out.print(scanner.next());
System.out.print(scanner.next());
System.out.println();
scanner.next();
dataCount += 3;
}
Otherwise, if the input is not well-formed, check with hasNext() before each next() call if you need to break the loop there.

Try it that way:
Scanner scanner = new Scanner(new File(file));
int dataCount = 0;
while(scanner.hasNext())
{
String[] line = scanner.nextLine().split(",");
for(String e : line) {
if (!e.matches("-?\\d+")) System.out.println(e);;
}
System.out.println();
dataCount++;
}
}
We will go line by line, split it to array and check with regular expression if it is integer.
-? stays for negative sign, could have none or one
\\d+ stays for one or more digits
Example input:
Ebor,Guyra,90
Warsaw,Paris,1000
Output:
Ebor
Guyra
Warsaw
Paris

I wrote a method called intParsable:
public static boolean intParsable(String str)
{
int n = -1;
try
{
n = Integer.parseInt(str);
}
catch(Exception e) {}
return n != -1;
}
Then in your while loop I would have:
String input = scanner.next();
if(!intParsable(input))
{
System.out.print(input);
System.out.println();
dataCount++;
}

Why the array seem to be longer than its maximum length?

Im new, I try to write some code, its for counting the string letter, space, and such. So, i set array length 50. But when i run the code later and enter more than 50 characters, it still can be run,and the total count can be more than 50, why? thank you.
import java.util.Scanner;
public class javaexcrises {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
String astrg = new String();
char[] ch = new char[50];
int charcount=0;
int spaccount=0;
int numcount=0;
int othcount=0;
System.out.println("Please enter some word ");
if(scan.hasNextLine()){
astrg = scan.nextLine();
ch = astrg.toCharArray();
int i;
for(i=0;i<astrg.length();i++){
if(Character.isLetter(ch[i])){
charcount++;
}
else if(Character.isDigit(ch[i])){
numcount++;
}
else if(Character.isSpaceChar(ch[i])){
spaccount++;
}
else{
othcount++;
}
}
System.out.println("Character = "+charcount);
System.out.println("Space = "+spaccount);
System.out.println("Number = "+numcount);
System.out.println("Others ="+othcount);
System.out.println("Total = "+ch.length);
}
scan.close();
}
}

ch = astrg.toCharArray();
toCharArray() returns a reference to a NEW array, and that reference replaces the old one that you allocated. That new array is large enough to contain the entire input string.

When we do astrg.toCharArray(), It returns a newly allocated character array, whose length is the length of this string and whose contents are initialized to contain the character sequence represented by this string.
If you remove new char[50] also it will not affect.

What's wrong with this file Scanner code?

I am trying to search the File for characters in Java language. For that I am using Scanner to scan the file.
Well to check the Heirarchy work, I am using System.out.print("Worked till here!"); so that I can check whether it is executed or not. I was able to execute the code till the last stage, but then I found that the essential boolean variable wasn't altered, which was under the condition to check whether there is a character match or not.
The file contents are as
Ok, here is some text!
Actually this file is created to test the validity of the java application
Java is my favourite programming language.
And I think I can score even more :)
Wish me luck!
However, no matter what I search it always prompts me to be false.
Here is the code I am using
public static void main (String[] args) throws IOException {
// Only write the output here!!!
System.out.print("Write the character to be found in the File: ");
Scanner sc = new Scanner(System.in);
String character = sc.next();
// Find the character
System.out.println("Searching now...");
getCharacterLocation(character);
// Close the resource!
sc.close();
}
The method call executed and the method is as
public static void getCharacterLocation (String character) throws IOException {
System.out.println("File found...");
File file = new File("res/File.txt");
Scanner sc = new Scanner(file);
int lineNumber = 0;
int totalLines = 0;
boolean found = false;
// First get the total number of lines
while(sc.hasNextLine()) {
totalLines++;
sc.nextLine();
System.out.println("Line looping! For Total Lines variable.");
}
int[] lineNumbers = new int[totalLines];
int lineIndex = 0;
System.out.println("Searching in each line...");
while(sc.hasNextLine()) {
// Until the end
/* Get each of the character, I mean string from
* each of the line... */
while(sc.hasNext()) {
// Until the end of line
String characterInLine = sc.next();
if(sc.findInLine(character) != null) {
found = true;
}
}
System.out.print(sc.nextLine() + "\n");
lineNumber++;
sc.nextLine();
}
System.out.println("Searching complete, showing results...");
// All done! Now post that.
if(found) {
// Something found! :D
System.out.print("Something was found!");
} else {
// Nope didn't found a fuck!
System.out.println("Sorry, '" + character +
"' didn't match any character in file.");
}
sc.close();
}
Never mind the extra usage of variables, and arrays. I would use it in further coding if I can get the character and set the value to true.
Here is the output of this program.
Initial Stage
This is the initial stage for that. I wrote Ok in the input field, you can see Ok is the very first character in the File too.
Final Stage
This is the result after the execution.
Any help in this?

You count lines and don't restart the scanner.
boolean found = false;
// First get the total number of lines
while(sc.hasNextLine()) {
totalLines++;
sc.nextLine();
System.out.println("Line looping! For Total Lines variable.");
}
int[] lineNumbers = new int[totalLines];
int lineIndex = 0;
System.out.println("Searching in each line..."); // <------
while(sc.hasNextLine()) {
add e.g.
UPDATED from the comment
sc.close();
sc = new Scanner(file);
before the next while(sc.hasNextLine())

You need to implement a way to string your characters together and check them against your input. It appears that you don't currently have a way to do this in your code.
Try building an array of characters with your scanner, and moving through and doing a check of your input vs the indexes. Or maybe there is a way to implement the tonkenizer class achieve this.
Put remember, what you are looking for is not a character, it is a string, and you need to keep this in mind when writing your code.

When you count your lines you use while(sc.hasNextLine()).
After this loop, your scanner is behind the last line, so when you go to your next loop while(sc.hasNextLine()) { it is never executed.

There are multiple problems with your code:
You Iterated through your scanner here:
while(sc.hasNextLine()) {
totalLines++;
sc.nextLine();
System.out.println("Line looping! For Total Lines variable.");
}
So after this you have to reset it again to read for further processing.
While searching for character you are having two loops:
while(sc.hasNextLine()) {
// Until the end
/* Get each of the character, I mean string from
* each of the line... */
while(sc.hasNext()) {
// Until the end of line
String characterInLine = sc.next();
if(sc.findInLine(character) != null) {
found = true;
}
}
Here you just need a single loop like:
while(sc.hasNextLine()) {
String characterInLine = sc.nextLine();
if(characterInLine.indexOf(character) != -1) {
found = true;
break;
}
}

String operation in Java

Is this code correct? I have mentioned my doubts in the form of comments in some places:
public class pract1
{
public static void main (String[] args)
{
int i;
String [] array = new String[20]; // Is this declaration correct?
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter the Array: ");
array = br.readLine(); // Is this the correct way to accept input from keyboard?
i=0;
while(array[i]!='\0') // Can I use the null pointer concept in Java?
{
System.out.println("The "+(i+1)+"character is:" +array[i]+"\n"); //Want to print each and every characters in string along with its position
i++;
}
}
}

This is how you could also do it:
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class Pract1
{
public static void main (String[] args)
{
String array = ""; //initialize an empty string that will hold the value from the keyboard
BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); // initialize the BufferedReader
// while "stop" is not typed on the console, keep running
while(!array.equals("stop")) {
System.out.println("Enter the Array: ");
try {
array = br.readLine(); // read from the console
System.out.println("Array:" + array);
for(int i=0; i<array.length(); i++) { //loop through the input and show the chars
System.out.println("Character "+(i+1)+" is: " +array.charAt(i));
}
} catch (Exception e) { // catch any exception and show only the message, not the entire stackTrace
System.out.println("Error: " + e.getMessage());
}
System.out.println("");
}
}
}

Java string is an object, not array. If you are more comfortable with array, use split() to get an array of String. You should note that each element in the derived array is String Object with only one letter, not primitive Char.
String[] array = "abc".split("");
for(int i; i< array.length; i++)
{
System.out.println("The "+(i+1)+"character is:" +array[i]+"\n");
}
You may want to read this Question to get the idea of String Object in Java Difference between "char" and "String" in Java

Array declaration
String [] array = new String[20]; // Is this declaration correct?
This declaration is correct for an array of 20 slots of type String (all of them initialized to null). But you might not need this right away, or not in this form.
You don't need to initialize the variable, especially if you overwrite that initialization by an instruction like: array = ....
Getting Input
array = br.readLine(); // Is this the correct way to accept input from keyboard?
Yes, readLine() is the way to go, but as the doc states, and as you will be told by the compiler, readLine(); does not return an array of Strings but a single String. You should use a String variable instead:
// initialize a String variable 'line' containing the whole line without the '\n' at the end
String line = br.readLine();
UPDATE: You could also use the Scanner class instead, that's usually what we do. Then, use sc.nextLine() for similar results as br.readLine(), as stated there.
Printing the chars
System.out.println("The "+(i+1)+"character is:" +array[i]+"\n");
//Want to print each and every characters in string along with its position
You can access the character at a given position in a String via the method charAt(int). Also, you don't have to deal with complicated C stuff such as looking for the end of the string via '\0'. You should instead use a proper for loop, like this:
String line = br.readLine();
for (int i = 0; i < line.length(); i++) {
System.out.println("The "+(i+1)+" character is: " + line.charAt(i) +"\n");
}
An alternate solution would be to use the toCharArray() method:
String line = br.readLine();
char[] chars = line.toCharArray();
for (int i = 0; i < chars.length; i++) {
System.out.println("The "+(i+1)+" character is: " + chars[i] +"\n");
}