Java SE native Data Type

Java SE 2:

1. Windows: notepad, editplus, ultraedit, gvim
Linux: VI, Vim, gedit

2. Data Types in Java are classified into two categories:
1) primitive data type)
2) Reference Type)

3. Variables and constants: the so-called constants, that is, the amount of values that do not change; the so-called variables, that is, the values can change
.

4. How to define variables?

Variable name;
Int;

5. How to assign values to variables?

Variable name = variable value;
A = 2;

= Indicates a value assignment. The value on the right of the equal sign is assigned to the variable on the left.
In Java, = is equivalent to = in mathematics.

6. Define and assign values to variables.

Variable name;
Variable name = variable value;

Int;
A = 1;

You can combine the above two steps into one:

Variable type variable name = variable value;
Int A = 1;

7. variable name: in Java, the variable name starts with an underscore, a letter, and a $ symbol, followed by an underscore,
Letters, $ characters, and numbers. In short, the variable name in Java cannot start with a number.

There are eight native Data Types in Java:
1) Integer type: int type. (32-bit)
2) byte: byte. (-128 ~ 127 integers between 256 ). 3) Short INTEGER: represented by short. (16 bits)
4) Long Integer: Long is used. (64-bit)

8. Data Representation in computer systems
Bit: Bit (only in the 0, 1 states), which is the smallest Data Representation Unit in the computer system.
Bytes: byte, 1 byte = 8 bit.
1 kb = 1024 bytes (1Kg = 1000 GB, different from the computer system)
1 MB = 1024 KB
1 GB = 1024 MB

9. comment. Annotations are for people, not for computers. Java has three types of Annotations:
1) single line comment: starts with //, and all the content following // is treated as comment.
2) multi-line comment: starts with/* and ends with */. All content in the middle is treated as comment. Multi-line comment comes from
C/C ++. Note that multi-line comments cannot be nested.
3) another multi-line comment. Used to generate the Java Doc help document. This document is not for the time being.