Java.io.Console class in Java

09 Jan, 2017
The Java.io.Console class provides methods to access the character-based console device, if any, associated with the current Java virtual machine. The Console class was added to java.io by JDK 6.
Important Points:
It is used to read from and write to the console, if one exists.
Console is primarily a convenience class because most of its functionality is available through System.in and System.out. However, its use can simplify some types of console interactions, especially when reading strings from the console.
Console supplies no constructors. Instead, a Console object is obtained by calling System.console( ), which is shown here:static  Console console( )If a console is available, then a reference to it is returned. Otherwise, null is returned. A console will not be available in all cases. Thus, if null is returned, no console I/O is possible.
static  Console console( )
If a console is available, then a reference to it is returned. Otherwise, null is returned. A console will not be available in all cases. Thus, if null is returned, no console I/O is possible.
It provides methods to read text and password. If you read password using Console class, it will not be displayed to the user.The java.io.Console class is attached with system console internally.
Important Methods:
writer : Retrieves the unique PrintWriter object associated with this console.Syntax:public PrintWriter writer() 
Returns: The printwriter associated with this console
public PrintWriter writer() 
Returns: The printwriter associated with this console
reader : Retrieves the unique Reader object associated with this console.Syntax:public Reader reader()  
Returns: The reader associated with this console

public Reader reader()  
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.Syntax:public Console format(String fmt, Object... args)
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.
Returns:This console
Throws: IllegalFormatException 

public Console format(String fmt, Object... args)
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.
Returns:This console
Throws: IllegalFormatException 

printf : A convenience method to write a formatted string to this console’s output stream using the specified format string and arguments.Syntax:public Console printf(String format, Object... 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.
Returns:This console
Throws:IllegalFormatException 

public Console printf(String format, Object... 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.
Returns:This console
Throws:IllegalFormatException 

readLine : Provides a formatted prompt, then reads a single line of text from the console.Syntax:public String readLine(String fmt,Object... args) 
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.
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
IOError - If an I/O error occurs.

public String readLine(String fmt,Object... args) 
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.
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
IOError - If an I/O error occurs.

readLine : Reads a single line of text from the console.Syntax:public String readLine() 
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 

public String readLine() 
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 

readPassword: Provides a formatted prompt, then reads a password or passphrase from the console with echoing disabled.Syntax:public char[] readPassword(String fmt,Object... args)
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.
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 
IOError
public char[] readPassword(String fmt,Object... args)
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.
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 
IOError
readPassword : Reads a password or passphrase from the console with echoing disabledSyntax:public char[] readPassword()
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
public char[] readPassword()
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
flush : Flushes the console and forces any buffered output to be written immediately .Syntax:public void flush()
Specified by: flush in interface Flushable
public void flush()
Specified by: flush in interface Flushable
Program:
// Java Program to demonstrate Console Methods  import java.io.*;class ConsoleDemo {    public static void main(String args[])     {        String str;                  //Obtaining a reference to the console.        Console con = System.console();                  // Checking If there is no console available, then exit.        if(con == null)         {            System.out.print("No console available");            return;        }                  // Read a string and then display it.        str = con.readLine("Enter your name: ");        con.printf("Here is your name: %s\n", str);          //to read password and then display it        System.out.println("Enter the password: ");        char[] ch=con.readPassword();          //converting char array into string        String pass = String.valueOf(ch);        System.out.println("Password is: " + pass);    }}
Output:
Enter your name: Nishant Sharma
Here is your name: Nishant Sharma
Enter the password: 
Password is: dada

Note: System.console() returns null in an online IDE
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