Constants and binary in 1.Java
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)
Binary, octal, decimal, hex
In the form of a binary representation:
Binary: Start with 0b
Octal: Starting with 0
Hex: Starts with 0x
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.
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.
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)
Data type variable name = variable value;
2. Data type:
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:
The range you can use
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.
Assigning a value of a large data type to a variable of a small data type
(data type) value or variable
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:
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!
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