Module java.base
Package java.io

Class Console

  • All Implemented Interfaces:
    Flushable
    public final class Console
	extends Object
		implements Flushable
    Methods to access the character-based console device, if any, associated with the current Java virtual machine.

    Whether a virtual machine has a console is dependent upon the underlying platform and also upon the manner in which the virtual machine is invoked. If the virtual machine is started from an interactive command line without redirecting the standard input and output streams then its console will exist and will typically be connected to the keyboard and display from which the virtual machine was launched. If the virtual machine is started automatically, for example by a background job scheduler, then it will typically not have a console.

    If this virtual machine has a console then it is represented by a unique instance of this class which can be obtained by invoking the System.console() method. If no console device is available then an invocation of that method will return null.

    Read and write operations are synchronized to guarantee the atomic completion of critical operations; therefore invoking methods readLine(), readPassword(), format(), printf() as well as the read, format and write operations on the objects returned by reader() and writer() may block in multithreaded scenarios.

    Invoking close() on the objects returned by the reader() and the writer() will not close the underlying stream of those objects.

    The console-read methods return null when the end of the console input stream is reached, for example by typing control-D on Unix or control-Z on Windows. Subsequent read operations will succeed if additional characters are later entered on the console's input device.

    Unless otherwise specified, passing a null argument to any method in this class will cause a NullPointerException to be thrown.

    Security note: If an application needs to read a password or other secure data, it should use readPassword() or readPassword(String, Object...) and manually zero the returned character array after processing to minimize the lifetime of sensitive data in memory. 

    
	 Console cons;
	 char[] passwd;
	 if ((cons = System.console()) != null &&
		 (passwd = cons.readPassword("[%s]", "Password:")) != null) {
		 ...
		 java.util.Arrays.fill(passwd, ' ');
	 }

    Since:
    1.6

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void flush()
      Flushes the console and forces any buffered output to be written immediately .
      Console format​(String fmt, Object... args)
      Writes a formatted string to this console's output stream using the specified format string and arguments.
      Console printf​(String format, Object... args)
      A convenience method to write a formatted string to this console's output stream using the specified format string and arguments.
      Reader reader()
      Retrieves the unique Reader object associated with this console.
      String readLine()
      Reads a single line of text from the console.
      String readLine​(String fmt, Object... args)
      Provides a formatted prompt, then reads a single line of text from the console.
      char[] readPassword()
      Reads a password or passphrase from the console with echoing disabled
      char[] readPassword​(String fmt, Object... args)
      Provides a formatted prompt, then reads a password or passphrase from the console with echoing disabled.
      PrintWriter writer()
      Retrieves the unique PrintWriter object associated with this console.