Java Basics under Chapter I (Java format, base type, operator)

First, Java basic format

public class demo1{//class name to be the same as the file name

public static void Main (string[] args) {//wrap each line, four spaces indent

System.out.println ("Hello World"); Output Hello World

End of statement ends with a semicolon

}

}

II. Basic data types

Integral type:

1.byte: Between byte-type 8-bit -128~127.

2.short: Short integer 16-bit -32768~32767.

3.int: Integer 32-bit.

4.long: Long integer 64 bits//end preferably plus l

Floating point type:

1.float: Single precision 32 bits//end preferably plus f.

2.double:64 bit double precision.

Character type:

Char: Character type//' single quotation mark contains example: char a = ' a ';

Boolean type:

Boolean: The Boolean value is: True/false.

Three, implicit conversion (from small to large conversion)

Byte,short,char-->int-->long-->float-->double

Example: int a = 10;

Long B = A;

B is implicitly converted to a long type.

Iv. Casting (conversion from large to small)

Format: (cast type) variable or value.

Note: The use of casts is generally not recommended.

Example: int a = 10;

byte B = (byte) A;

Five, type compatible

Char is only compatible with shaping

Example: char a = "a";

int b = A;

B-->65

Vi. operators

1. Arithmetic operators

+ +,--, +,-, *,/,%

2. Relational operators

, <,! =, = =, >=, <=

3. Logical operators

&&, &, | |, |,!

&&, | | Differences with &, |

&&, &--> When the result of the first expression determines the overall result, it is not executed at a later time.

&, | --regardless of whether the first expression is true/false, the last expression is executed.

Example: int a = 1;

int b = 2;

int c = 3;

int D;

D = b > A | | b > C;

Since B > A was established, B > C was not executed.

Java Basics under Chapter I (Java format, base type, operator)