Java Basic Learning Notes--4 (Basic data type)

3. Java Basic type

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1) Int: integral type

1.1) the direct amount of a number is of type int (the so-called direct quantity is the value that is written directly, such as int a = 10000;)

1.2) Two int operation, the result is an int type, and the decimal bit is unconditionally discarded ( such as: int A=5/3; result is a=1)

1.3) Range -2^31 ~ ~ 2^31-1, overrun may occur in the range, you need to avoid

2) Long: Length-integer

2.1) long direct quantity, after integer plus L or l

2.2) Value range -2^63 ~ ~ 2^63-1

2.2) JDK provides a way to get the current system time: System.currenttimemillis (), gets the time from 1970.1.1 0 o'clock to now, returns a long type value

3) Double: floating-point, double-precision

3.1) The direct amount of decimals is double by default (for example: double d = 1.023; ), if you use float to represent decimals, you need to add F or F later

3.2) scientific notation means: 3.14E2, 3.14e2,3.14e-2, etc., such as: 3.14E2 means 3.14 times 10 2

3.2) With rounding error, use with caution when precise operation (for example: double D = 3.0-2.9; after calculation d = 0.10000000000000009;)

4) Char: Character type

4.1) char is actually a 16-bit unsigned integer with a value range of 0~~65535, so char can directly define integers (such as: char C = 123;)

4.2) Char defines the variable when the value is placed in the single quote ' ', is characters in Unicode encoded format (e.g. char c = ' Medium ',)

4.3) when defining a char variable, you can take an escape character (e.g. char C1 = ' \u0041 '; char c2 = ' \ n ')

escape character	meaning
' \ n '	represents a carriage return
' \ r '	represents a newline character
' \ \ '	represents a backslash (\)
' \ '	denotes single quotation mark (')
‘\"‘	Represents double quotation marks (")

5) Boolean: Boolean, 1-byte

5.1) Boolean direct amount, only true and false,true indicate that the condition is set, false indicates not valid

(For example: boolean flag = true;)

4. Conversion of data types

Represents the range of values from small to lower as shown below

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1) automatic type conversion: From small type to large type

2) Forced type conversions: from large types to small types, strong turns can occur: loss of precision, overflow

Case 2:

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Java Basic Learning Notes--4 (Basic data type)