- All Implemented Interfaces:
Flushable
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 may 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
Modifier and TypeMethodDescriptioncharset()
Returns theCharset
object used for theConsole
.void
flush()
Flushes the console and forces any buffered output to be written immediately.Writes a formatted string to this console's output stream using the specified format string and arguments.boolean
Returnstrue
if theConsole
instance is a terminal.A convenience method to write a formatted string to this console's output stream using the specified format string and arguments.reader()
Retrieves the uniqueReader
object associated with this console.readLine()
Reads a single line of text from the console.Provides a formatted prompt, then reads a single line of text from the console.char[]
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.writer()
Retrieves the uniquePrintWriter
object associated with this console.
-
Method Details
-
writer
Retrieves the uniquePrintWriter
object associated with this console.- Returns:
- The printwriter associated with this console
-
reader
Retrieves the uniqueReader
object associated with this console.This method is intended to be used by sophisticated applications, for example, a
Scanner
object which utilizes the rich parsing/scanning functionality provided by theScanner
:Console con = System.console(); if (con != null) { Scanner sc = new Scanner(con.reader()); ... }
For simple applications requiring only line-oriented reading, use
readLine(java.lang.String, java.lang.Object...)
.The bulk read operations
read(char[])
,read(char[], int, int)
andread(java.nio.CharBuffer)
on the returned object will not read in characters beyond the line bound for each invocation, even if the destination buffer has space for more characters. TheReader
'sread
methods may block if a line bound has not been entered or reached on the console's input device. A line bound is considered to be any one of a line feed ('\n'
), a carriage return ('\r'
), a carriage return followed immediately by a linefeed, or an end of stream.- Returns:
- The reader associated with this console
-
format
Writes a formatted string to this console's output stream using the specified format string and arguments.- Parameters:
fmt
- A format string as described in Format string syntax.args
- Arguments referenced by the format specifiers in the format string. If there are more arguments than format specifiers, the extra arguments are ignored. The number of arguments is variable and may be zero. The maximum number of arguments is limited by the maximum dimension of a Java array as defined by The Java Virtual Machine Specification. The behaviour on anull
argument depends on the conversion.- Returns:
- This console
- Throws:
IllegalFormatException
- If a format string contains an illegal syntax, a format specifier that is incompatible with the given arguments, insufficient arguments given the format string, or other illegal conditions. For specification of all possible formatting errors, see the Details section of the formatter class specification.
-
printf
A convenience method to write a formatted string to this console's output stream using the specified format string and arguments.An invocation of this method of the form
con.printf(format, args)
behaves in exactly the same way as the invocation ofcon.format(format, args)
- Parameters:
format
- A format string as described in Format string syntax.args
- Arguments referenced by the format specifiers in the format string. If there are more arguments than format specifiers, the extra arguments are ignored. The number of arguments is variable and may be zero. The maximum number of arguments is limited by the maximum dimension of a Java array as defined by The Java Virtual Machine Specification. The behaviour on anull
argument depends on the conversion.- Returns:
- This console
- Throws:
IllegalFormatException
- If a format string contains an illegal syntax, a format specifier that is incompatible with the given arguments, insufficient arguments given the format string, or other illegal conditions. For specification of all possible formatting errors, see the Details section of the formatter class specification.
-
readLine
Provides a formatted prompt, then reads a single line of text from the console.- Parameters:
fmt
- A format string as described in Format string syntax.args
- Arguments referenced by the format specifiers in the format string. If there are more arguments than format specifiers, the extra arguments are ignored. The maximum number of arguments is limited by the maximum dimension of a Java array as defined by The Java Virtual Machine Specification.- Returns:
- A string containing the line read from the console, not
including any line-termination characters, or
null
if an end of stream has been reached. - Throws:
IllegalFormatException
- If a format string contains an illegal syntax, a format specifier that is incompatible with the given arguments, insufficient arguments given the format string, or other illegal conditions. For specification of all possible formatting errors, see the Details section of the formatter class specification.IOError
- If an I/O error occurs.
-
readLine
-
readPassword
Provides a formatted prompt, then reads a password or passphrase from the console with echoing disabled.- Parameters:
fmt
- A format string as described in Format string syntax for the prompt text.args
- Arguments referenced by the format specifiers in the format string. If there are more arguments than format specifiers, the extra arguments are ignored. The maximum number of arguments is limited by the maximum dimension of a Java array as defined by The Java Virtual Machine Specification.- Returns:
- A character array containing the password or passphrase read
from the console, not including any line-termination characters,
or
null
if an end of stream has been reached. - Throws:
IllegalFormatException
- If a format string contains an illegal syntax, a format specifier that is incompatible with the given arguments, insufficient arguments given the format string, or other illegal conditions. For specification of all possible formatting errors, see the Details section of the formatter class specification.IOError
- If an I/O error occurs.
-
readPassword
public char[] readPassword()Reads a password or passphrase from the console with echoing disabled.- Returns:
- A character array containing the password or passphrase read
from the console, not including any line-termination characters,
or
null
if an end of stream has been reached. - Throws:
IOError
- If an I/O error occurs.
-
flush
-
charset
Returns theCharset
object used for theConsole
.The returned charset corresponds to the input and output source (e.g., keyboard and/or display) specified by the host environment or user. It may not necessarily be the same as the default charset returned from
Charset.defaultCharset()
.- Returns:
- a
Charset
object used for theConsole
- Since:
- 17
-
isTerminal
public boolean isTerminal()Returnstrue
if theConsole
instance is a terminal.This method returns
true
if the console device, associated with the current Java virtual machine, is a terminal, typically an interactive command line connected to a keyboard and display.- Implementation Note:
- The default implementation returns the value equivalent to calling
isatty(stdin/stdout)
on POSIX platforms, or whether standard in/out file descriptors are character devices or not on Windows. - Returns:
true
if theConsole
instance is a terminal- Since:
- 22
-