# Learning experience

• Hump ​​nomenclature: class names are nouns that start with a capital letter, capitalize the first letter of each word.

• java main method does not return value

• Use the java doc

• 

• Floating-point value does not apply to unacceptable financial calculations rounding error in using bigdecemial

• Escape character codes explained before: for example, "\ u0022 + \ u0022" is not composed of a plus sign string surrounded by quotation marks (U + 0022). In fact, \ u0022 is converted before parsing ", which will get is an empty string.

• For strictfp method key mark must be strictly point calculations to generate reproducible results.

• public class jj {    public static void main(String[] args) {        int a = 10%-3;        int b = -10%3;        int c = -10%-3;        System.out.println(a+","+b+","+c);    }}

  

  Take the remainder were close to zero.

  

floorMod into a downward modulo.

• 

• Casts are cut off, Math.round to rounding.

• Determined using short time.

• String all = String.join(
  " / ", "S", "M",
  "L", "XL"
  );
  // all is the string "S / H / L / XL"

• null value detecting

• Console cons = System.console(); 
  String username = cons.readLine("User name: ")； 
  char [] passwd = cons.readPassword("Password:");

  For security reasons, the password is stored in the return of the one-dimensional array of characters instead of a string. After the cryptographic processing, it should be immediately covered with a padding value array element (array process will be described in Section 3.10).

• Formatted output:

  

  

  

• foreach statement format:

  for (type element type variable element value: traverse the object obj) {

  　　　　Java statement quoted the x;　　

  }

• Using this syntax can re-initialize an array without creating a new variable. For example: small Primes = new int[] { 17, 19, 23,29, 31, 37 }This is a short form of the following statement:int[] anonymous = { 17, 19, 23, 29, 31, 37 }; smallPrimes = anonymous

• static int binarySearch (type [] a , int start, int end, type v)
  using a binary search algorithm to find the value v. If found, the corresponding index value is returned; otherwise, returns a negative value r. -r-1 is ordered to maintain a v should be inserted.

• In all methods in a class in the class instance variables can not be named in the same domain name.

• Getxxx return value accessor methods must be immutable objects such as String, and if the object is returned inevitably mutable objects, e.g. Date, clone the object is returned.

  class Emloyee{
      public Date getHireDay(){
          return (Date)hireDay.clone();
      }
  }

• If there are front final modification example domain, the construction of this object must be initialized when such domain.

• NumberFormat currencyFormatter = NumberFormat.getCurrencylnstance(); 
  NumberFormat percentFormatter = NumberFormat.getPercentInstance();
  double x = 0.1; 
  System.out.println(currencyFormatter.format(x)); // prints $0.10 
  System.out.println(percentFomatter.format(x)); // prints 10%

  A similar approach is referred to as a factory method.

• If a class is provided in at least one constructor, but did not provide a no-argument constructor, so if no argument when constructing the object is considered illegal.

• End does not make sense, do not Transcription, and directly draw focus. . .