Java Learning Notes (ii)

I. Java COMMON data types

Data type	Occupied bytes	Attention
Int	4
Char	2
Double	8
Float	4	float a=2f; (must add F or f otherwise he will default to double)
Boolean	1	Only true or False no 0 or not 0
String		is a String type
Long/short int	8/2
Byte	1	1 bytes to 8 bits

Two. Data type conversion

1. Auto Convert: Byte->short int->char->int->long int->float->double

Conversion condition: The variable type does not change from a low type to a high type (that is, the arrow refers to the conversion direction), but the calculated value becomes a high type

2. Coercion type conversion (data type) variable name such as char A; (int) A---------A is cast to an int type such as

The double type of the a=3.2 is cast to the int type, and is automatically shed. 2. Conversion from high-precision to low-precision will lose precision.

Three. naming rules in Java

First, naming norms

1, the project name all lowercase

2. Package name All lowercase

3. The first letter of the class name is capitalized, if the class name consists of multiple words, the first letter of each word is capitalized.

such as: public class myclass{}

4, the variable name, the method name first letter lowercase, if the name is composed of multiple words, the first letter of each word should be capitalized.

such as: int index=0;

public void ToString () {}

5, the constant name all uppercase

such as: public static final String game_color= "RED";

6. All naming rules must follow the following rules:

1), the name can only be composed of letters, numbers, underscores, $ symbols

2), cannot start with a number

3), name cannot use keywords in java.

4), not to be allowed to appear in Chinese and pinyin naming.

Two. Notes

Single-line Comment

/* Multiline Comment */

Four. Operators

Arithmetic operator: +,-,*,/,% (the number of both sides must be integer), + + (self-increment),-i-subtract. (Note the difference between i++ and ++i)

Relationship: >,<,! =,<=,>=,==

Assignment operator: =

Logical operators:&& with, or | |, non-! ,& continuous road with, | no short circuit or. (no short-circuit means)

The bitwise operator: .....

Trinocular operator:a=a>0?b:c;

If a is greater than 0,a=b, otherwise a=c;

2. Priority level:

Java Learning Note (b)