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java.io
Class Console
java.lang.Object
java.io.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
|
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. |
Methods inherited from class java.lang.
Object
|
clone
,
equals
,
finalize
,
getClass
,
hashCode
,
notify
,
notifyAll
,
toString
,
wait
,
wait
,
wait
|
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(java.lang.String, java.lang.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. 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 fmt,
Object... args)
-
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 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(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.
An invocation of this method of the form
con.printf(format, args)
behaves in exactly the same way as the invocation of
con.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 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.
readLine
public String readLine(String fmt,
Object... args)
-
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
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 fmt,
Object... args)
-
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
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
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
public void flush()
-
Flushes the console and forces any buffered output to be written immediately .
-
-
Specified by:
-
flush
in interface
Flushable
-