Class Console

java.lang.Object

java.io.Console

All Implemented Interfaces:: Flushable

public sealed 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's console exists 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 generally exist and will be connected to the keyboard and display from which the virtual machine was launched. If the standard input or standard output have been redirected (for example, to a file or to a pipe), or if the virtual machine was started from a background job scheduler, the console will not exist.

If the console exists, then it is represented by a unique instance of this class which can be obtained by invoking the System.console() method. If the console does not exist, 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.

Read and write operations use the Charsets specified by stdin.encoding and stdout.encoding, respectively. The Charset used for write operations can also be retrieved using the charset() method. Since Console is intended for interactive use on a terminal, these charsets are typically the same.

Operations that format strings are locale sensitive, using either the specified Locale, or the default format Locale to produce localized formatted strings.

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 Type	Method	Description
`Charset`	`charset()`	Returns the `Charset` object used for the write operations on this `Console`.
`void`	`flush()`	Flushes the console and forces any buffered output to be written immediately.
`Console`	`format(String format, Object... args)`	Writes a formatted string to this console's output stream using the specified format string and arguments with the `default format locale`.
`Console`	`format(Locale locale, String format, Object... args)`	Writes a formatted string to this console's output stream using the specified format string and arguments with the specified `locale`.
`boolean`	`isTerminal()`	Returns `true` if the `Console` instance is a terminal.
`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 with the `default format locale`.
`Console`	`printf(Locale locale, 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 with the specified `locale`.
`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 format, Object... args)`	Provides a formatted prompt using the `default format locale`, then reads a single line of text from the console.
`String`	`readLine(Locale locale, String format, Object... args)`	Provides a formatted prompt using the specified `locale`, 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 format, Object... args)`	Provides a formatted prompt using the `default format locale`, then reads a password or passphrase from the console with echoing disabled.
`char[]`	`readPassword(Locale locale, String format, Object... args)`	Provides a formatted prompt using the specified `locale`, then reads a password or passphrase from the console with echoing disabled.
`PrintWriter`	`writer()`	Retrieves the unique `PrintWriter` object associated with this console.

Methods declared in class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Modifier and Type	Method	Description
`protected Object`	`clone()`	Creates and returns a copy of this object.
`boolean`	`equals(Object obj)`	Indicates whether some other object is "equal to" this one.
`protected void`	`finalize()`	Deprecated, for removal: This API element is subject to removal in a future version. Finalization is deprecated and subject to removal in a future release.
`final Class<?>`	`getClass()`	Returns the runtime class of this `Object`.
`int`	`hashCode()`	Returns a hash code value for this object.
`final void`	`notify()`	Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()`	Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()`	Returns a string representation of the object.
`final void`	`wait()`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
`final void`	`wait(long timeoutMillis)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis, int nanos)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

Method Details

writer

public PrintWriter writer()

Retrieves the unique PrintWriter object associated with this console.

Returns:: The printwriter associated with this console

reader

public Reader reader()

Retrieves the unique Reader 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 the Scanner:

    Console con = System.console();
    if (con != null) {
        Scanner sc = new Scanner(con.reader());
        ...
    }

For simple applications requiring only line-oriented reading, use readLine(String, Object...).

The bulk read operations read(char[]), read(char[], int, int) and read(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. The Reader's read 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

public Console format(String format, Object... args)

Writes a formatted string to this console's output stream using the specified format string and arguments with the default format locale.

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 behavior on a null 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.

format

public Console format(Locale locale, String format, Object... args)

Writes a formatted string to this console's output stream using the specified format string and arguments with the specified locale.

Parameters:: locale - The locale to apply during formatting. If locale is null then no localization is applied.; 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 behavior on a null 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.
Since:: 23

printf

public 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 with the default format locale.

Implementation Requirements:: This is the same as calling 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 behavior on a null 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

public Console printf(Locale locale, 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 with the specified locale.

Implementation Requirements:: This is the same as calling format(locale, format, args).
Parameters:: locale - The locale to apply during formatting. If locale is null then no localization is applied.; 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 behavior on a null 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.
Since:: 23

readLine

public String readLine(String format, Object... args)

Provides a formatted prompt using the default format locale, then reads a single line of text from the console.

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 behavior on a null argument depends on the conversion.
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

public String readLine(Locale locale, String format, Object... args)

Provides a formatted prompt using the specified locale, then reads a single line of text from the console.

Parameters:: locale - The locale to apply during formatting. If locale is null then no localization is applied.; 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 behavior on a null argument depends on the conversion.
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.
Since:: 23

readLine

public String readLine()

Reads a single line of text from the console.

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:: IOError - If an I/O error occurs.

readPassword

public char[] readPassword(String format, Object... args)

Provides a formatted prompt using the default format locale, then reads a password or passphrase from the console with echoing disabled.

Parameters:: format - 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 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 behavior on a null argument depends on the conversion.
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(Locale locale, String format, Object... args)

Provides a formatted prompt using the specified locale, then reads a password or passphrase from the console with echoing disabled.

Parameters:: locale - The locale to apply during formatting. If locale is null then no localization is applied.; format - 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 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 behavior on a null argument depends on the conversion.
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.
Since:: 23

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

public void flush()

Flushes the console and forces any buffered output to be written immediately.

Specified by:: flush in interface Flushable

charset

public Charset charset()

Returns the Charset object used for the write operations on this Console.

The returned charset is used for encoding the data that is sent to the output (e.g., display), specified by the host environment or user. It defaults to the one based on stdout.encoding, and may not necessarily be the same as the default charset returned from Charset.defaultCharset().

Returns:: the Charset object used for the write operations on this Console
Since:: 17

isTerminal

public boolean isTerminal()

Returns true if the Console instance is a terminal.

This method always returns true, since System.console() provides a Console instance only when both standard input and output are unredirected, that is, when running in an interactive terminal.

Returns:: true if the Console instance is a terminal
Since:: 22

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