"Java" Learning Notes (1)

Java data type:

Base data type: (variable in stack) numeric: byte ( 1 short ( 2 bytes)   int (four bytes)   long ( 8 float ( 4 bytes)   double ( 8 bytes)

Character type:char(2 bytes)

Boolean type:boolean

Reference data type (variable reference in the heap): Class interface array

Cannot replace true or false with 0 or not 0

Java uses 8 bytes to represent a long with 2 bytes for a char, and the characters to use Unicode encoding can also ' \u+16 ' denotes a character.

8 binary number with 0 beginning hexadecimal number starting with 0x binary number with 0b

There is no unsigned number in Java, you can use a long type to handle four-byte unsigned numbers

The default shape is int If you use long after +l

Floating-point thousands of points can be underlined: 123_456.789_000 = = 123456.789

Float type defaults to double , to represent floating-point numbers after +f

Identifiers: Can be combined with alphanumeric _ $ to begin with cannot be a number

Java is case sensitive, the class name is capitalized with the rest of the first letter lowercase, constants are defined with use

Arithmetic operators:15/4(z integer division) 15.0/2(real division)

Java logical operators:&&(short circuit and) | | (short circuit or)

Bitwise operations:>>>(unsigned number right shift) highest bit 0(normal right shift >>highest bit complement original sign bit int is to + bit taking mode Long is to - bit-taking mode)

String Connector +

The declaration method of an array int []a = new int[3];

the Java array is a reference type, and once the space is allocated, each element is implicitly initialized, the value type is 0, and the reference type is NULL .

The properties of an array can be specified in length by . length .

The enhanced for statement makes it easy to access the elements in it:

int []ages = new int [10];

for (int age:ages)

{

System.out.plintln (age);

}// read-only traversal

Methods for copying arrays:

Example of copying a source.length element starting from subscript 0 to the destination array in the source array (sources) from subscript 0 location to begin storage.

Array.copy (Source,0,dest,0,source. Length);

Declaration methods for two-dimensional arrays:

int [][]t = new int [3][];

T[0] = new int [2]

T[1] = ...

T[2] = ...

Multidimensional arrays should be declared in order from high to low dimensions, unlike C + + .

"Java" Learning Notes (1)