![]() ![]() Once the stream is closed, we can no longer access the input from the Scanner.īesides closing itself, the Scanner class will also close the InputStream if it implements Closeable. When working with it, the Scanner will always expect more input until the InputStream is closed. Problems When Using System.in With ScannerĪ big problem with System.in is that it's an InputStream. There are type-specific methods such as hasNextInt(), hasNextFloat(), hasNextLine() etc. Scans the next token of the input into a boolean value and returns that value.Īdvances this scanner past the current line and returns the input that was skipped.Ī method worth noting is the hasNext() method - a generic method that will return true if there's any type of token to be read. Scans the next token of the input as a short. Scans the next token of the input as a long. Scans the next token of the input as an int. Scans the next token of the input as a float. Scans the next token of the input as a double. Scans the next token of the input as a byte. Scanner Methods for ReadingĪvailable methods for reading the next token using the scanner method are: Methodįinds and returns the next complete token from the scanner. The easiest way to do this is via the try-with-resources statement. Note that Scanner has to be closed when you're done working with it. ![]() Additionally, as the second argument, it can specify a character encoding to interpret said characters by: Scanner sc = new Scanner( new FileInputStream( "myFile.txt"), "UTF-8") It can take any File, InputStream, Readable, ReadableByteChannel, Path (of a file to read), or even String. Read a line until newline or EOF into a stringĪgain, the constructor doesn't have to take System.in. Read a byte into a variable byte myByte = sc.nextByte() Read an integer into a variable int myInteger = sc.nextInt() Let's see how we can extract information from a Scanner into variables we can work with: Scanner sc = new Scanner(System.in) This Scanner instance can now scan and parse booleans, integers, floats, bytes and Strings. Since System.in is just an InputStream, we can construct a Scanner as such: Scanner sc = new Scanner(System.in) The class is a simple scanner that can parse and handle primitive inputs, Strings and streams. In the end, we'll Decorate the InputStream class and implement our own custom UncloseableInputStream to handle issues with the Scanner class. Since Scanner has some downfalls, we'll also be using the BufferedReader and InputStreamReader classes to process the System.in stream. We're going to use Scanner class to make our interaction with the underlying stream easier. You may recognize it as Java's System.in. We're going to focus on keyboard input via something called the standard input stream. User input can come in many forms - mouse and keyboard interactions, a network request, command-line arguments, files that are updated with data relevant for a program's execution, etc. Reading user input is the first step towards writing useful Java software. ![]()
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