2day

JAVA Cross-platform sex ：JVM The virtual machine itself does not allow cross platform , What allows cross platform is java Program .

JRE and JDK and JVM The role of ：1、 When writing code, you will use JRE Has been written in java Code

                                           2、 When compiling code, you will use JDK Compilation tools in

                                           3、 When running code, you will use JDK Running tools in

                                           4、 The code runs in JVM in

 

Why configure “Path” environment variable ： Not configured path Environment variables can only be in bin Only in the directory can javac and java Tools , In the future, the code will be placed in bin The directory is not easy to manage ; With the path Environment variables can then be in any directory ( Folder path ) Next , All have access to bin In the directory javac and java Tools .

Classification of notes

Single-line comments ：// Annotation information

Multiline comment ：/* Annotation information */

Documentation Comments ：/** Annotation information **/

Comments will not be involved in the operation of the code

keyword ： Keyword means to be java English words with specific meanings ; Characteristic is ： The letters are all lowercase , Code editing tools will color keywords .

identifier ： Give class , Method , Symbol of variable name ; By digital , Letter , Underline and dollar sign make up 、 Cannot start with a number 、 It can't be a keyword 、 Case sensitive 、 You can't have Spaces .