JAVA programming language - excerpt Notes

JAVA programming language design (Elementary) notes excerpt

• To avoid input errors, do not nextByte(), nextShort(), nextInt()etc. later usenextLine()

  nextXXXXX()Are referred to 令牌读取方法, they will read tokens separated by delimiters.
  next()Read a character string delimited by delimiters, and nextLine()the read row line to a separator end.
  Token reading method can not be read back of the token separator. If the token is called after reading method nextLine(), which is read from the start delimiter, the delimiter line end of the line of characters. The line separator is also read, but it is not nextLine()returned string portion.

  For example, the following documents 34 567

  Execute code 1:

  Scanner input = new Scanner(new File("test.txt"));
  int intValue = input.nextInt();
  String line = input.nextLine();

  intValueValue of 34, and the linecharacter contains the ` ，. 5 ，. 6 ，7 '.

  If the input is entered from the keyboard ( 34carriage return):

  Execute code 2:

  Scanner input = new Scanner(System.in);
  int intValue = input.nextInt();
  String line = input.nextLine();

  It will be intValuea value of 34, and lineis an empty string. The reason is that the token reading method nextInt()reads 34, then stops at the separator, where the separator is a line separator (Enter). nextLine()After reading method will line separator, then return line before the string delimiters. Because there are no characters before the line separator, it lineis empty.

• Common escape character

\ B backspace

\ T Tab key

\ N linefeed

\ F feed

\ R Enter key

\ Backslash

\ `Single quotes

\ " Double quotes

• Common identifiers

% B Boolean value

% C character

% D decimal integer

% F float

% E standard form Scientific Notation Number

% S string

• Examples of the development width and precision

% 5c outputs a character and in front of the character entry box plus 4

% 6b Boolean output, a space in front of false, true before the two spaces

% 5d output integer entries, a width of at least 5, if the entry is less than 5 digits, the spaces. Otherwise automatically increase width.

Float% 10.2f output width of at least 10, including decimal and decimal places. Thus, before the decimal point is assigned to 7, the same space if less than the excess automatically increase the width.

% 10.2e output width floating point entry is at least 10, including decimal places and two decimal exponent part. Shortage and excess above.

% 12s output string width of at least 12. Ibid.