Getting Started with Java-object-oriented basics

Getting Started with Java-object-oriented

• The difference between the public class and class declaration classes:
  1. public class Life: The file name must be the same as the class name
  2. The file name and class name can be inconsistent when the class declaration
  3. A file can have multiple class-defined classes, but only a class that is defined by a public class
• Recommendations for writing identifiers
  1. Do not use too many symbols, preferably starting with letters
  2. can have uppercase and lowercase letters, underscores, numbers, $
  3. Cannot start with a number
• Data types are classified as "base data type", "Reference data Type"
  1. 1. Basic

        Integer type	Byte	Short	int long
        Floating-point types	Float	Double
        Character type	Char
        Boolean type	Boolean

     2. Reference

        Class	Class
        Interface	Interface
        Array

• Overflow of data

   Public classDateDemo02 {/**     * @paramargs*/     Public Static voidMain (string[] args) {//TODO auto-generated Method Stub        intmax=Integer.max_value; System.out.println (The maximum value for int is: "+max); System.out.println ("The maximum value of int +1 is:" + (max+1)); System.out.println ("The maximum value of int +2 is:" + (max+2)); System.out.println ("The maximum value of int +3 is:" + (max+3)); }}

  The results of the operation are as follows:

  The maximum value of int is: The maximum value of 2147483647int +1 is:The maximum value of -2147483648int +2 is: -2147483647int the maximum value of +3 is:- 2147483646

  Will cause data errors, but the program will not error.

You can use forced type conversions to prevent data overflow:

 Public classDateDemo02 {/**     * @paramargs*/     Public Static voidMain (string[] args) {//TODO auto-generated Method Stub        intmax=Integer.max_value; System.out.println (The maximum value for int is: "+max); System.out.println ("The maximum value of int +1 is:" + (max+1l)); System.out.println ("The maximum value of int +2 is:" + ((Long) max+2)); }}

The results are as follows:

The maximum value of int is: The maximum value of 2147483647int +1 is:The maximum value of 2147483648 int +2 is: 2147483649

Getting Started with Java-object-oriented basics