Java Data Types

There are only two types of variables in Java: Basic Data Type (8 types) and reference data type.

State Changes in memory when variables are defined: Define data types, open up space, and store data.

The memory space of each of the eight basic data types and the value range of the variables

Byte 1 byte short 2 bytes int 4 bytes long 8 bytes (do you know why? Haha, because the computer can only process up to sixty-fourteen bits at once, 8 bytes = 64bit .)

The scope and lifecycle of the variable. Pay attention to the problem of repeated definition of the variable (as long as the variable name is the same, the definition is repeated)
Type conversion of variables (automatic increase of expression type, forced type conversion, especially char)