Java Learning Path (i) Java basics

Identifiers (Naming conventions)

　　Identifiers are composed of letters, numbers, underscores, ￥, $, and Chinese;

The first letter cannot use numbers;

Cannot duplicate the system keyword;

Length Unlimited, case-sensitive;

Class Name: capitalize each initial letter;

Package name: all lowercase;

Method Name: First word lowercase, other first letter capitalized;

Variable: lowercase;

Constant: Uppercase;

Basic data types

Integer	byte byte type Short Quick-integer int integer Long integer type	Basic data types
Floating point number	Double Dual Precision Type Float Single precision Type
BYTE type	Char 0-65535
Boolean type	Boolean (True, False)
Array		Reference data type
Class, interface

Variable

Definition and Assignment: Data type variable name = value; Example: int b = 123;

In the process of the operation, the capacity of the small size of the conversion capacity of large, large capacity of small conversion capacity;

1         int a = 3; 2         int b = 6; 3         byte c = (byte) (A+B);

Boolean logical operators

a	b	! A	! b	a&b	a | b	a&&b	a | | b	a^b
true	true	false	false	true	true	true	true	false
true	false	false	true	false	true	false	true	true
false	true	true	false	false	true	false	true	true
False	False	True	True	False	False	False	False	False

Logical NON (! ): Not true or false. It's not fake.

XOR (^): Same as false. The difference is true;

or (|): As long as one is true;

With (&): As long as there is a false is the false;

Three mesh operator: judgment statement? "For true execution", "for false execution";

Array

1         /**2 * Define static arrays3 * data type [] Variable name = {value};4          */5         int[] A = {};6         intB[] = {-};7         /**8 * Define dynamic arrays9 * data type [] Variable name = new data type "array maximum length";Ten          */ One         int[] C =New int[5]; A         /** - * Define two-dimensional arrays -          */ the         int[] D = {{1,2,3},{4,5,6}}; -         int[] e =New int[2] [2];

Method and Construction method

    /**      * Method Definition     * [modifier]  return value type     method name (parameter  ) {     *         method Body     *}     * parameter definition: Data type  variable name     * return value type: void (no return value), base data type     * Method invocation: Method name ();      */     Public void name () {        }    /**     * Constructor Method     * Modifier    class name () {     *      *}     * method call:     *         class name Variable name = new class name ();      */

Object

Invocation of the object: type variable name = new Type ();

Type generally refers to the class file name;

Modifier

Public	Have access to
Private	Privatization. This kind of Chinese Academy of Sciences visit
Default	The default modifier, which can be accessed within the same package
Protected	This class, subclass, and package can be accessed

Inheritance: extends (keywords)

Cast: instanceceof (keyword)

Final: The final modification cannot be changed, cannot be inherited, cannot be rewritten;

Abstract class:

Modified with abstract;

cannot be instantiated directly;

Abstract method is used to modify the method.

Abstract classes are generally used as parent classes of other classes, but must be rewritten;

Cannot have the main method;

Abstract methods are only declared, not implemented;

　　

Java Learning Path (i) Java basics