Flushablepublic sealed class Console extends Object implements 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.
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, ' ');
}
| 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 |
Writes a formatted string to this console's output stream using the specified format string and arguments with the default format locale. |
Console |
format |
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 |
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 |
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 |
Provides a formatted prompt using the default format locale, then reads a single line of text from the console. |
String |
readLine |
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 |
Provides a formatted prompt using the default format locale, then reads a password or passphrase from the console with echoing disabled. |
char[] |
readPassword |
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. |
public PrintWriter writer()
PrintWriter object associated with this console.public Reader reader()
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.
public Console format(String format, Object... args)
default format locale.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.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.public Console format(Locale locale, String format, Object... args)
locale.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.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.public Console printf(String format, Object... args)
default format locale.format(format, args).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.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.public Console printf(Locale locale, String format, Object... args)
locale.format(locale, format, args).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.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.public String readLine(String format, Object... args)
default format locale, then reads a single line of text from the console.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.null if an end of stream has been reached.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.public String readLine(Locale locale, String format, Object... args)
locale, then reads a single line of text from the console.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.null if an end of stream has been reached.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.public String readLine()
null if an end of stream has been reached.IOError - If an I/O error occurs.public char[] readPassword(String format, Object... args)
default format locale, then reads a password or passphrase from the console with echoing disabled.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.null if an end of stream has been reached.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.public char[] readPassword(Locale locale, String format, Object... args)
locale, then reads a password or passphrase from the console with echoing disabled.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.null if an end of stream has been reached.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.public char[] readPassword()
null if an end of stream has been reached.IOError - If an I/O error occurs.public Charset charset()
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().
Charset object used for the write operations on this Console
public boolean isTerminal()
true if the Console 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.
isatty(stdin/stdout) on POSIX platforms, or whether standard in/out file descriptors are character devices or not on Windows.true if the Console instance is a terminal
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