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This article mainly explains "what is the basic grammar of Java". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what is the basic grammar of Java"?

Prepare for work Dos command

Configure environment variables

Understand the difference between jdk, jre, and jvm

Environment variable configuration: JAVA_HOME in Path is the installation directory of jdk, add% JAVA_HOME%\ bin to Path

API source code read [src.zip]

Some html syntax is used in the source code

Start-- JAVA basic grammar notes

Multiline comments / * /

Documentation Notes / * * /-- javadoc generate help documentation

Identifier-keyword

Any place where you can name yourself is called an identifier. For example: variable name, method name, class name, interface name, package name

Naming rules:

Consists of 26 uppercase and lowercase letters, 0-9, _ or $

Numbers cannot begin.

Keywords and reserved words cannot be used, but can contain keywords and reserved words.

In Java, it is strictly case-sensitive and unlimited in length.

Identifiers cannot contain spaces.

Command specification:

Variable, method-- myVariable, myMethod (xxYyZz)

Class, interface-MyClass (uppercase), MyInterface (XxYyZz)

Package-packet (xxyyzz)

Constants are all capitalized and words are separated by "_"-DEFAULT_SIZE (XX_YY_ZZ)

Variable

Strongly typed language

Data type, variable name, stored value type varName [= value]

Data type basic data type

Type Bytes Integer byte1

Short2

Int (default) 4

Long8 floating point number float4

Double (default) 8-character char2 Boolean Boolean 1 bit

Note:

The number of char bytes in java, which is 2 bytes, different from c (one byte)''has and only one character

With regard to the "default" problem, for example, 233 does not write a suffix and is stored on the computer according to int (4 bytes), but if it is written as 233L, it is stored according to long (8 bytes), and the more commonly used one is float, which is also followed by the suffix f, which is different from the default float type.

Financial computing, using BigDecimal

Escape character'\ u0000'

5.char can declare a character, or it can represent an escape character ('\ n'), or it can directly use the unicode value to represent a character-type constant ('\ u0043')

Write as\ n so that there is no escape.

6. Character set, there is garbled (conversion stream of IO stream)

ASCII → Unicode (specific landing is UTF-8)

When writing a file to determine the encoding type, such as ANSI (that is, GBK), the file form that exists on disk is in GBK form, only then can it be read normally in cmd (support GBK), but if the save form is changed to UTF-8, it will appear "garbled".

Type transformation

Only 7 data types (excluding boolean) have type conversions discussed here.

Automatic type conversion-low to high

In particular, byte,short,char are not converted to each other, and they are first converted to int type byte + byte → int byte + short → int in the calculation.

Regulation: Java is doing the operation. If the Operand is within the range of int, all operations will be performed according to int.

Forced type conversion-from high to low

Note: in basic data types, low represents fewer bytes, and in classes, low represents subclasses.

Long l = 123232L

Float f = 33.223F

Reference data type type occurrence form class class-- String interface interface array int [] arrays

Key point: String type variable

"" null is acceptable (char is not allowed)

String str1 = 123 (wrong) String str1 = 123 + "" (correct)

String can operate with 8 basic types (including boolean), and the operation can only be a join symbol: +

When concatenating the value of any basic data type with a string (String), the value of the basic data type is automatically converted to the String type

Connect to boolean, directly connect to true or false

/ / practice 1char c = 'averse; / / 97 A:65int num = 10 string str = "hello"; System.out.println (c + num + str); → 107helloSystem.out.println (c + str + num); → ahello10System.out.println (c + (num + str)); → a10helloSystem.out.println (str + num + c); → hello10a// exercise 2 / print * * System.out.println (' * +'\ tasking +'*') Char + char-- > int (93) System.out.println ('*'+ "\ t" +'*'); char + String-> String (* *) System.out.println ('*'+\ tasking + "*"); (51 *) System.out.println ('*'+ ('\ tasking + "*")); (* *)

Practice

Operator

Arithmetic operator

Assignment operator

Comparison operator (distinguish between = and =)

Logical operator (& and & relation)

Bit operator

Three-digit operator

Format: X? Y: Z = = > if x is true, take y; if false, take z

Double num = remainn)? "m big": ((m big n)? "m and n are equal": "n big")

Compare the maximum of three numbers

Int max1 = (N1 > N2)? N1: N2 int max2 = (max1 > n3)? Max1: n3

Note:

Priority: logic non-> logic and > logic or

Symbol +, there are some skills to use.

"" +'a complete string addition'

However, it becomes the number 97.

Process control

Sequential structure

Select structure

The switch statement starts at the matching case tag based on the value of the expression and executes all the way to the break statement or the end of the switch statement. If the value of the expression does not match any of the case values, enter the default statement if there is a default statement.

Loop structure continue: launch this loop and continue to execute the next loop

Enhanced for cycle foreach

Scanner user interaction System.in

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