Java Language Console I/O Reading user input from the console
Example
Using BufferedReader:
System.out.println("Please type your name and press Enter.");
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
try {
String name = reader.readLine();
System.out.println("Hello, " + name + "!");
} catch(IOException e) {
System.out.println("An error occurred: " + e.getMessage());
}
The following imports are needed for this code:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
Using Scanner:
Java SE 5
System.out.println("Please type your name and press Enter");
Scanner scanner = new Scanner(System.in);
String name = scanner.nextLine();
System.out.println("Hello, " + name + "!");
The following import is needed for this example:
import java.util.Scanner;
To read more than one line, invoke scanner.nextLine() repeatedly:
System.out.println("Please enter your first and your last name, on separate lines.");
Scanner scanner = new Scanner(System.in);
String firstName = scanner.nextLine();
String lastName = scanner.nextLine();
System.out.println("Hello, " + firstName + " " + lastName + "!");
There are two methods for obtaining Strings, next() and nextLine(). next() returns text up until the first space (also known as a "token"), and nextLine() returns all text that the user inputted until pressing enter.
Scanner also provides utility methods for reading data types other than String. These include:
scanner.nextByte();
scanner.nextShort();
scanner.nextInt();
scanner.nextLong();
scanner.nextFloat();
scanner.nextDouble();
scanner.nextBigInteger();
scanner.nextBigDecimal();
Prefixing any of these methods with has (as in hasNextLine(), hasNextInt()) returns true if the stream has any more of the request type. Note: These methods will crash the program if the input is not of the requested type (for example, typing "a" for nextInt() ). You can use a try {} catch() {} to prevent this (see: Exceptions)
Scanner scanner = new Scanner(System.in); //Create the scanner
scanner.useLocale(Locale.US); //Set number format excepted
System.out.println("Please input a float, decimal separator is .");
if (scanner.hasNextFloat()){ //Check if it is a float
float fValue = scanner.nextFloat(); //retrive the value directly as float
System.out.println(fValue + " is a float");
}else{
String sValue = scanner.next(); //We can not retrive as float
System.out.println(sValue + " is not a float");
}
Using System.console:
Java SE 6
String name = System.console().readLine("Please type your name and press Enter%n");
System.out.printf("Hello, %s!", name);
//To read passwords (without echoing as in unix terminal)
char[] password = System.console().readPassword();
Advantages:
- Reading methods are synchronized
- Format string syntax can be used
Note: This will only work if the program is run from a real command line without redirecting the standard input and output streams. It does not work when the program is run from within certain IDEs, such as Eclipse. For code that works within IDEs and with stream redirection, see the other examples.
