JDK and JRE interpretation
JDK Java Development Kits 【重点】
JAVA development tools
JDK = JRE + development tools
JRE Java Runtime Environment 【重点】
JAVA runtime environment
JRE = JVM (Java Virtual Machine) + core class libraries
Configuring JDK environment
My Computer - Properties - Advanced System Settings
Variable name: JAVA_HOME
Variable value: D: \ Program Files \ Java \ jdk1.8.0_211
New:
variable name: CLASS_PATH
variable values:;.% JAVA_HOME% \ lib ;% JAVA_HOME% \ lib \ tools.jar
Review:
variable name: path
to add content:
;% JAVA_HOME% \ bin;% JAVA_HOME% \ jre \ bin;
Eight basic data types
| Integer | Take up memory space | data range |
|---|---|---|
| byte | 1 byte (8bit) | -128 ~ 127 |
| short | 2 bytes (16bit) | -32768 ~ 32767 |
| int | 4 bytes (32bit) | -2^31 ~ 2^31 - 1 |
| long | 8 bytes (64bit) | -2^63 ~ 2^63 - 1 |
| Float | Take up memory space | data range |
|---|---|---|
| float | 4 bytes (32bit) | ±3.4×10^38 |
| double | 8 bytes (64bit) | 10^308 |
| Character | Take up memory space | data range |
|---|---|---|
| char | 2 bytes (16bit) | Able to save Chinese |
| Boolean | Take up memory space | data range |
|---|---|---|
| boolean | Subject to availability | true false |
Identifier needs to meet the hump nomenclature or underscore nomenclature
Hump nomenclature [common]
. A small hump nomenclature
requirement identifier is lowercase first letter of each word capitalized after
the iPhone iTouch iMax macOS
ageOfStudent getStudentName
applies to:
the method and variable names
. B big hump nomenclature
requires each identifier the first byte of a word is capitalized
String Person FileUpLoad LoginFilter
apply to:
name of the class or interface name