Basic naming rules and data types in the Java basic article No2--java

Source: Internet
Author: User

Tags: existing run local variable binary conversion bool range byte sign negative number

Constants and binary in 1.Java
1. Constants:
In the process of running the program, can not change the amount, is the constant

A Boolean value can only be true or false
NULL: null constant, no representation exists!


---------------------------below are the things to know-----------------------------------
2. Binary: (Learn)
Common in-system:
Binary, octal, decimal, hex

In the form of a binary representation:
Binary: Start with 0b
Octal: Starting with 0
Hex: Starts with 0x

Binary conversions:
Any binary into decimal:
Coefficient * The power of the cardinality, sum.

Decimal goes to any binary:
The remainder is removed from the base.

Fast Conversion method: 8421 yards
------------------------------------------------------------------------------

Original code, anti-code, complement:
1. All content in the computer is stored in complementary form

2. We can not directly understand the complement, must be converted into the original code to understand.

3. Anti-code is the complement converted into the original code of the transfer content.


Normal Condition:
Complement-----> Anti-code----> Original Code


I usually write the original code----> anti-code----> complement

Positive number: The original code is the same as the anti-code complement.

Negative:
The original code to reverse code: the highest bit unchanged, others 0 change to 0

Anti-code to complement: anti-code +1



2. Variable, data type conversion (Key Mastery)

1. Variables
1. Format:
Data type variable name = variable value;

2. Data type:
1. Classification:
Basic data types
Four types of eight types:
Integer type: byte short int long
Float type: float double
Boolean Type: Boolean
Character type: Char

BYTE range: -128~127
Short range: ( -2^15) ~ (2^15-1)

Reference data type: Talk about the Object!

2. An integer is not identified, the default is int type
If it is a decimal, there is no identity, the default is double type

3. Precautions for use of variables:
1. Scope:
Effective interval.
The range you can use

2. Initialize:
Local variables (variables defined in the method)
Before use, you must assign a value first.
You can define not to use, and you do not need to initialize.

3. A statement can declare multiple variables.

4. Data type conversions:
1. Implicit conversions:
Small data types are calculated with large data types, and small data types are automatically promoted to large data types before they are calculated.

2. Cast:
Assigning a value of a large data type to a variable of a small data type

(data type) value or variable

int x=100;

byte B = (byte) x;

3.byte Short Char These three types of variables are automatically raised to type int when they are being operated on.

4. Constant optimization mechanism:
When compiling the source code, the compiler checks that there are constants in operation, and will automatically complete the constant operation before compiling into the bytecode file.

Byte b=3+4;====> is equivalent to byte b=7;

Range of values for 5.float and long types:
The range of float is larger than the range of type long because the storage structure of the underlying float is different.

6. Value range of data type:
byte < Short,char < int < Long < float < double

7. (char) character type:
There are two types of patterns:
1. Characters
2. Integer (each character corresponds to a code value in the Code table: ' A ' =97)

' A ' =97
' A ' =65
' 0 ' =48

Value range for char type: 0~65535

Char type can be stored in Chinese!

8. String:
Strings can be added to any other data type, actually connecting,
It can turn the value of any data type into a string and then concatenate it to produce a new string.

3. Operator (Key Mastery)
1. Arithmetic operators
%: The remainder of dividing two numbers

/: Divide two number of quotient, two integers, get no decimal.


++,--:
When used alone, whether in front of the variable or behind, there is no difference between the variable is self-increment

In the operation, if the + + symbol is in front of the variable, the variable is self-increment and then the value after the increment is calculated.

If the + + symbol is followed by a variable, the variable is self-increment and then the value before the increment is calculated.

+ + and--with a cast effect

2. Assignment operators
=,+=,-=,*=,/=,%=

The left side of the assignment operator must be a variable.

+ =: The variable on the left side of the operator is evaluated with the variable or constant on the right, and the result is assigned to the left variable.

+ = or other special assignment operators have the effect of casting.


3. Comparison operators
> >= < <= = = =!

The result of the comparison operator operation is a Boolean type!

Basic naming rules and data types in the Java basic article No2--java

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