First sight of JAVA-Scanner & process control-primary evolution 04

Scanner

Function: realize the interaction between the program and people

next():

You can end the input after reading a valid character
The blanks encountered before entering valid characters will be removed
next () can not get a string with spaces

nextLine():

Enter the end, you can get a blank

Scanner scanner = new Scanner(System.in);
System.out.println("开始接收输入");
    String str = scanner.nextLine();
    System.out.println(str);
scanner.close();

java is a strongly typed language

basic type

byte 1B

short 2B

Int 4B

long 8B

float 4B (use with caution, about =)

double 8B

用BigDecimal

char 2B

String! is the class

boolean 1b

Reference type

Except 8 basic types are reference types

Forced conversion

High-low

overflow

Loss of accuracy

Automatic conversion

Low-high

variable

Class variable static

Instance variable: subordinate to the object, there is a default value if it is not initialized by itself, the default value of boolean is false, and the default value is null except for basic types

Local variables must be declared and initialized

constant

static final

Variable capitalization

Operator

When performing operations on different basic types of data

Convert long with long

Convert int without long

a++，++a

Auto-increment after executing the code

Bit operation

Extremely efficient

,<< *2

String concatenation+

The content has a string, it will become String

But there are operations in front of the string, and then it becomes a String

Ternary operator

X ？a；b

X judgment, true output a; false output b

Other methods: nextInt(), nextFloat()

select

if

Once the judgment is true, skip after execution

Single choice: if(){};

Double choice: if(){}else{}

Multiple choices: if(){}elseif{}else{}

switch

Failure to add break will cause case penetration
jdk7 began to support strings
Support char and string

cycle

while

Most need to stop the loop, need an expression invalidation to end the loop
In a small number of cases, it is necessary to loop and always perform such as server request response monitoring

dowhile

The difference between while and dowhile

while: judge first and then execute

dowhile: execute first and then judge, execute at least once

for

for(;;）

Perform the initialization step first, you can declare a type, you can initialize one or more loop control variables, or it can be empty

Update loop variables after executing a loop

for(x:n)

For arrays and collections

break和continue

break: exit the loop

continue: jump to this loop, continue to the next loop

goto

Don’t need to master it, rarely use now