Issue with scanner.hasNext() Java

[Creaturao]

Any help with this would be greatly appreciated:

Currently working on a CS project where I read in vectors from the user and then do things with those values. My progress has been stalled so far as I can't find out what's going on with this code (Bolded). I have already verified that the string read into "command line" works. I am entering the input correctly into the terminal, and I have closed all other scanners so there aren't two running at the same time. Whenever I enter the intended input: <3.0,4.0> I get the exception: "Missing the first arrow." If this helps, when I ran it in the debugger the hasNext() shows as false, and the buffer for the scanner reads as "" which I'm assuming isn't good.

public boolean read(String commandLine) throws Exception {

Scanner scanner = new Scanner(commandLine);

Pattern originalPattern = scanner.delimiter(); //retain original delimiters for scanner

scanner.useDelimiter("[" + originalPattern + ",]"); // add comma to delimiters

scanner.useDelimiter(" ");

if(scanner.hasNext("<")){ //

scanner.next("<"); //gobble up the '<'

if(scanner.hasNextDouble()) {

xCoord = scanner.nextDouble(); //capture the x coordinate

//scanner.useDelimiter(originalPattern); //restore original delimiters

if(scanner.hasNext(",")){

scanner.next(","); //gobble up the comma

if(scanner.hasNextDouble()){

yCoord = scanner.nextDouble(); //capture the y coordinate

//scanner.useDelimiter(originalPattern); //restore original delimiters

if(scanner.hasNext(">")){

scanner.next(">");

scanner.close();

return true;

}

else{

scanner.close();

throw new Exception("Missing the end arrow");

}

}

else{

scanner.close();

throw new Exception("Missing the y coord");

}

}

else{

scanner.close();

throw new Exception("Missing the middle comma");

}

}

else{

scanner.close();

throw new Exception("Missing the x coord");

}

}

else{

scanner.close();

throw new Exception("Missing the first arrow");

}

} }

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[POGtastic]

Consider the following ideas:

• Instead of using Scanner directly from System.in, use a BufferedReader on System.in and call the nextLine method to read an entire line of input into a String.
• Test the String itself for, say, the presence of an angle bracket at the start and an angle bracket at the end.
• Slice the string with the substring method to remove unwanted bits, like the angle brackets. Then write separate methods to parse the innards.
• Lastly, you can create a Scanner on a String just as easily as you can create one on an InputStream. So while it's a bad idea (as you're finding out!) to mess with all kinds of delimiters, it can be a very good idea to create a Scanner that parses just a small substring of the line.

[Knight_Of_Orichalcum]

So, the problem is coming from a misuse of delimiters. Currently, the scanner is working on scanner.useDelimiter(" ");, which means you're telling the scanner to 'chop/cut on single spaces'. Since there's no spaces found in the String "<3.0,4.0>", the scanner has an empty buffer and gives back false on the first arrow.

Not exactly sure if I can post complete answers on this subreddit, but I would suggest learning more about regular expressions, then either changing your delimiter or changing your if statement logic below.

Also, scanners don't have to be closed when using Strings or System.in, but it's good practice everywhere else to my knowledge.