Java eight basic data types store numeric values, characters, and Booleans

Put the knowledge of Java in retrospect, or else forget it.

Basic data type: 4 classes of 8

Integer type

BYTE 1-128~127

Short 2

int 4

Long 8

Floating point Type

Float 4

Double 8

Character type

Char 2

Boolean type

Boolean 1

Different value ranges for memory space

Byte memory space 8

Short memory Space 16

int memory Space 32

Long Memory Space 64

Float Memory Space 32

Double Memory Space 64

1: When defining a long or float type variable, add either L or F.

integers are type int by default, and floating-point numbers are double by default.

Byte,short at the time of definition, they are actually receiving a value of type int.

This is self-made a data detection, if they are no longer within the scope of the error.

Problem with 2:byte value -128~127

One byte 01111111 127

BYTE B1 = 127;

byte b2 = (byte) 128; -128

byte B3 = (byte) 129; -127

byte b4 = (byte) 130; -126

Range of Byte: 128 ~ 127

127 01111111

-127:11111111

+1

------------------------

10000000

-128:10000000 (the highest bit is the sign bit, also the value bit) only at the critical time

3: Conversion of data type to the default conversion of small data types to large data types

Byte,short,char--INT--long--float--double

Long:8 bytes

Float:4 bytes

A: Their underlying storage structure is different.

The range of data represented by B:float is larger than the range of long

Long:2^63-1

float:3.4*10^38 > 2*10^38 > 2*8^38 = (2^3) ^38 = 2*2^114 > 2^63-1

4:java character Char in a language can store a Chinese character? Why?

OK. Because characters in the Java language occupy two of bytes.

The Java language uses Unicode encoding.

Constant: The amount of the value that does not change during program execution

Classification:

Literal constants

String constants

Integer constants

Decimal constants

Character constants can only be single characters

Boolean constant True and False

An empty constant array

Custom Constants

Binary: X-binary is every x into one

Binary consists of 0, 1 components 0b

Octal consists of 0-7 components 0

decimal integers are decimal by default

Hexadecimal by 0-9,a-f (can be uppercase) 0x

Binary conversion

Convert decimal in any binary

The method of position right expansion

Decimal conversion to arbitrary binary

In addition to the base fetch, until the quotient is zero, the remainder is reversed

Fast Conversion

8421 yards binary vs. decimal conversions

Octal grouping method for binary fast conversion

Binary fast conversion hexadecimal grouping method

Original code, anti-code, complement

There is a binary operation in the bottom of the computer

The data is calculated using the binary complement of the data.

The display uses the binary source code of the data.

The original inverse of the positive number is the same, the highest bit is the sign bit 0 The remaining bits are the value bits

Negative original code highest bit sign bit 1, remaining bit is value bit

The inverse code is the highest bit, the rest of the bits are reversed by bit

Complement anti-code +1

Variable:

The amount at which the value can change within a certain range during program execution

Equivalent to the unknown in mathematics

Define the format:

Data type variable name = initial value;

Constants of the same type

Implicit conversions exist in Java (default conversion)

(1): The Boolean type cannot be converted to another data type

(2): byte,short,char-int-long-float-double

(from the range of the small to the large range turn)

If an int type participates in an operation, the result must be an int type

If there is a long join operation, the result must be a long type

If a float participates in the operation, the result must be a float type

If there is a double to participate in the operation, the result must be double type

(3): Byte,short,char is not converted, they participate in the operation first converted to int type

Note: Large type turn small type may lose precision.

public class Datatyepdemo {public static void main (string[] args) {byte A = 3;int b = 4;int C = a+b; System.out.println (c);}}

There are also coercion type conversions

public class DataTyepDemo1 {public static void main (string[] args) {byte a =3;int b = 4;byte c = (byte) (A+B); System.out.println (c);}}

You find that the character corresponding to the int type should have a one by one corresponding relationship

Within a table

Ascii

' 0 ' 48

' A ' 97

' A ' 65

public class DataTypeDemo2 {public static void main (string[] args) {System.out.println ("Hello" + ' a ' +1); System.out.println (' a ' + 1 + "Hello"); System.out.println ("-------------"); System.out.println ("5+5=" +5+5); System.out.println (5+5+ "=5+5");}}

Results:

Helloa1

98hello

-------------

5+5=55

10=5+5

Considerations for using Variables

A: Scope issues

The variable is defined in the curly braces, and the range of the curly braces is the scope of the variable.

Two variables of the same name cannot be defined in the same scope.

B: Initialization value issue

No initialization value can be used directly

C: It is recommended to define only one variable on a single line

Multiple can be defined, but not recommended

Variable definition Format

Variable name of data type = initialization value;

Data type variable name;

Variable name = initial value;

public class Datetypenoticedemo {public static void main (string[] args) {int a = 10;int B = 10; System.out.println (a); System.out.println (b);}}

public class Datatypetest {public static void main (string[] args) {byte b = (byte) 130; System.out.println (b);}}

/*   Analysis:       130  int    type   4 bytes   32bit        original code  00000000  000000000 00000000 10000010    coercion is an arithmetic       complement   Get      after casting   complement  00000000 000000000 00000000 10000010  cast                 10000010   --------complement 10000001  --------Anti-code 11111110  ---------original code -126*/

public class DataTypeTest2 {public static void main (string[] args) {Float f1 = (float) 12.345;      In this 12.345 constant is a double type of 8 bytes//made a strong turn after the assignment to the float type variable System.out.println (F1); float F2 = 12.345f; Here 12.345 constants are the direct assignment of the float type System.out.println (F2);}}

Put in front of operand

Add (Subtract) first and then participate in the operation

Put behind the operand

First participate in the operation and then add (Subtract)

public class DataTypeTest3 {public static void main (string[] args) {int a = 10;int b = 10;int c = 10;a = b++;  A ten b c 10c =--a;  A 9 b one c 9b = ++a;  A ten B 9a = c--; A 9 b C 8system.out.println ("A:" +a); System.out.println ("B:" +b); System.out.println ("C:" +c);}}

Comparison operators

public class Operatordemo {public static void main (string[] args) {int a = 32;int B = 23; System.out.println (A==B); System.out.println (A>B); System.out.println (A!=B); System.out.println (B>=a);}}

This article from the "Clear Sky" blog, declined reprint!

Java eight basic data types store numeric values, characters, and Booleans