Class IO

java.lang.Object
java.lang.IO
public final class IO extends Object
A collection of static methods that provide convenient access to System.in and System.out for line-oriented input and output.

The readln() and readln(String) methods decode bytes read from System.in into characters. The charset used for decoding is specified by the stdin.encoding property. If this property is not present, or if the charset it names cannot be loaded, then UTF-8 is used instead. Decoding always replaces malformed and unmappable byte sequences with the charset's default replacement string.

Charset decoding is set up upon the first call to one of the readln methods. Decoding may buffer additional bytes beyond those that have been decoded to characters returned to the application. After the first call to one of the readln methods, any subsequent use of System.in results in unspecified behavior.

API Note:
The expected use case is that certain applications will use only the readln methods to read from the standard input, and they will not mix these calls with other techniques for reading from System.in.
Since:
25

  • Method Summary

    Modifier and Type
    Method
    Description
    static void
    print(Object obj)
    Writes a string representation of the specified object to the standard output.
    static void
    println()
    Writes a line separator to the standard output.
    static void
    println(Object obj)
    Writes a string representation of the specified object and then writes a line separator to the standard output.
    static String
    readln()
    Reads a single line of text from the standard input.
    static String
    readln(String prompt)
    Writes a prompt and then reads a line of input.

    Methods declared in class Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    Modifier and Type
    Method
    Description
    protected Object
    clone()
    Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
    boolean
    equals(Object o)
    Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.
    protected void
    finalize()
    Deprecated, for removal: This API element is subject to removal in a future version.
    May cause performance issues, deadlocks and hangs.
    final Class<? extends Object>
    getClass()
    Answers the unique instance of java.lang.Class which represents the class of the receiver.
    int
    hashCode()
    Answers an integer hash code for the receiver.
    final void
    notify()
    Causes one thread which is waiting on the receiver to be made ready to run.
    final void
    notifyAll()
    Causes all threads which are waiting on the receiver to be made ready to run.
    String
    toString()
    Answers a string containing a concise, human-readable description of the receiver.
    final void
    wait()
    Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).
    final void
    wait(long time)
    Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.
    final void
    wait(long time, int frac)
    Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

  • Method Details

    • println

      public static void println(Object obj)
      Writes a string representation of the specified object and then writes a line separator to the standard output.

      The effect is as if println(obj) had been called on System.out.

      Parameters:
      obj - the object to print, may be null

    • println

      public static void println()
      Writes a line separator to the standard output.

      The effect is as if println() had been called on System.out.

    • print

      public static void print(Object obj)
      Writes a string representation of the specified object to the standard output.

      The effect is as if print(obj) had been called on System.out.

      Parameters:
      obj - the object to print, may be null

    • readln

      public static String readln()
      Reads a single line of text from the standard input.

      One line is read from the decoded input as if by BufferedReader.readLine() and then the result is returned.

      If necessary, this method first sets up charset decoding, as described in above in the class specification.

      Returns:
      a string containing the line read from the standard input, not including any line separator characters. Returns null if an end of stream has been reached without having read any characters.
      Throws:
      IOError - if an I/O error occurs

    • readln

      public static String readln(String prompt)
      Writes a prompt and then reads a line of input.

      Writes a prompt as if by calling print, and then reads a single line of text as if by calling readln.

      If necessary, this method first sets up charset decoding, as described in above in the class specification.

      Parameters:
      prompt - the prompt string, may be null
      Returns:
      a string containing the line read from the standard input, not including any line separator characters. Returns null if an end of stream has been reached without having read any characters.
      Throws:
      IOError - if an I/O error occurs