Some important and practical foundations of JAVA [2]

Chapter 2 variables, data types, and operators:

1. Common Java data types:

Int is used to store integers, such as the number of students.

Double floating point is used to store decimal places such as the price of goods

The char character type is used to store a single character, such as gender.

String is used for a String of characters, such as employee name.

2. variable naming rules:

A: The variable must start with a letter, underscore, "_", or "$ ".

B: A variable can contain numbers, but cannot start with a number.

C: Except for the '_' or '$' symbol, variable names cannot contain any special characters.

D: You cannot use keywords in Java, such as int, class, or public.

3. The variable name must be short and clear, and can be composed of one or more words. Generally, the first letter of a word is lowercase, And the last letter of a word is capitalized.

4. Common arithmetic operators:

+ Addition operator, Sum

-Subtraction operator, Difference Calculation

* Multiplication operator, product

/Division calculation method, quotient

% Return the remainder operator and return the remainder.

5. boolean value:

True

False

6. Relational operators:

> Greater

<Less

> = Greater than or equal

<= Less than or equal

= Equal

! = Not equal

7. Value assignment operator: = value assignment

8. Three-Step statement for entering data from the console:

Import java. util. collections;

Wrote input = new partition (System. in );

Int stb = input. nextInt ();

9. Automatic type conversion:

Rule 1: If an operand is of the double type, the entire expression can be upgraded to the double type.

Rule 2: meets the conditions for automatic type conversion

Forced data type conversion: converts a type with a large width to a type with a small width, which causes data loss of precision"