2021-1-5
1. The role of JRE, JDK, JVM
2. Commonly used DOS commands
3. Environment variable configuration
1. The first step: create a new java_home 
2. The second step: configure the path path in the system variables
3. Compile and run HelloWorld through the cmd window
4. Detailed explanation of HelloWorld code (including public and class explanations)
5. Comment classification (single line, multiple lines, document notes)
6. The concept of constants
7. Data type (basic and reference)
8. Precautions for defining variables
9. Keyboard input, print output (Scanner)
Scanner
10. Identifier naming rules (big hump, small hump)
11. Data type conversion (implicit conversion and forced conversion)
1. Implicit conversion
2. Coercion
12. Operators and expressions
String + operation
13. Increment and decrement operators (understand)
14. Assignment operator (understand)
15. Comparison operators (understand)
16. Logical operators (understand)
17. Ternary Operator
