1. The transition between the numeric types
Five solid line represents conversion information is lost, there may be a broken line represents a conversion loss of accuracy.
2. cast
For example cast conversion between double and int
double x = 9.997;
int nx = (int)x;
Such values nx 9
If you want to variables rounding
double x=9.9997;
int nx = (int)Math.round(x);
3. String
String greeting = "Hello";
String s = greeting.substring(0,3)
The second parameter is the first position do not want to copy
4. immutable string
String string does not provide a method for modifying the string. If you want to "Hello" changed to "Help"
String substring may be used alternatively
greeting = greeting.substring(0,3)+"p"
Detecting whether strings quite
“Hello”.equals(greeting)
To detect whether two strings are equal, ignoring case strings
“Hello”.equalsIgnoreCase("Hello")
To check a string is neither null nor empty string, in this case the use of:
if(str!=null && str.length()!=0)
5. Some of the common string variable
char charAt (int index): returns the given code means
length (): returns the length of the string
substirng(int beginIndex)
substring (int beginIndex, int endIndex) Returns a new string
toLowerCase()
toUpperCase()
trim () spaces removed the head and tail of the original string
6. The file input and output
Scanner in = new Scanner(Path.get("myfile.txt"));
If the file name contains a backslash and other symbols,
“ c:\\mydirectory\\myfile.txt ”
To write to a file,
PrintWriter out = new PrintWriter("myfile.txt");
String name = in.nextLine();
To enter an integer, which use in.nextInt ()