Basic data type ：
plastic ：byte( position ),short( Short ),int( integer ),long( Long integer ); The default literal value is int type .
floating-point ：float( Single precision floating point ),double( Double precision floating point ); The default literal value is double type .Literal suffix ：
1. Integer type followed by uppercase L Or lowercase l -- Indicates that the literal value is long type
2. Decimal type followed by uppercase F Or lowercase f -- Indicates that the literal value is float type
3. Decimal type followed by uppercase D Or lowercase d -- Indicates that the literal value is double type Type conversion ：
Automatic type conversion ( From small to large / Implicit conversion )：
** Assign values or variables with small data type ranges to variables with large data type ranges **
Cast ( From big to small / Display conversion )：
** Assign a value or variable representing a large data range type to a variable representing a small data range type .( Pay attention to the conversion process **
** Data loss problem )**
