Reading Input from std
Scanner in = new Scanner(System.in);
String name = in.nextline(); // reads a line of input (contain spaces)
String firstName = in.next(); // reads a word (delimited by whitespace)
String age = in.nextInt(); // reads an integer如果要读密码，用 Console Class
Formatting std Output
printf method from the C library (bookmarked)
a format string can indicate the index of the argument to be formatted.
System.out.printf("%1$s %2$tB %2$te, %2$tY", "Due date:", new Date());
System.out.printf("%s %tB %<te, %<tY", "Due date:", new Date());The index must immediately follow the %, and it must be terminated by a $. (index start with 1, not 0)
Alternatively, you can use the < flag. It indicates that the same argument as in the preceding format specification should be used again.
like sprintf ➡️Concatenation
formatting date output (bookmarked)
File Input and Output
in
Scanner in = new Scanner(Path.of("myfile.txt"), StandardCharsets.UTF_8);
// "c:\\mydirectory\\myfile.txt"然后使用 Scanner 的 method 读就完了
❗️注意路径需要 Path.of method。如果按照 output 一样，这将会把这串字符串给了 Scanner
out
PrintWriter out = new PrintWriter("myfile.txt", StandardCharsets.UTF_8);
/* ...... */
out.flush();
out.close(); // 看起来必须有这个才能真的写入然后可以用 print 之类的操作 (但不是System.out)
如果使用了相对路径
那么起始路径是 java 虚拟机开始的地方
// You can find the directory location with this call:
String dir = System.getProperty("user.dir");