basic types, operators, expressions

control flow

if, if else, else if

loops (for, foreach, while, break, continue)

for

- go
```go
for i := 0; i < len(os.Args); i++ {
  fmt.Println(os.Args[i])
}
fmt.Println(s)

switch

• python
  • no switch-case in python

object or struct

pointers

functions

scope and external variables

• shell

f1(){
local xxx=1
echo $xxx;
echo "all variables in a function are global like in js, set it with local to make them local variables"
echo "local can only be used in a function"
}

pass by value and pass by reference

dynamic length variable

array

array to stream

• java

String[] array = {"a", "b", "c", "d", "e"};
Stream<String> stream1 = Arrays.stream(array);
stream1.forEach(x -> System.out.println(x));

array to map

list

initialization

access via index

add, upate the list

delete from the list

traverse the list

slice the list

sort the list

copy the list

• python

• python tuple

reverse the list

list to map

• java

Map<String, Item> map = list.stream().filter(
                vo -> !vo.getEnvType().equals("commercial"))
                .collect(
                        Collectors.toMap(vo -> String.join("@", vo.name(), vo.region()),
                                vo -> vo));

numeric list operations

map

initialization

add, update map

delete from map

traverse the map

enum

• java

// declare enum
public enum Day {
    MONDAY,TUESDAY,WEDNESDAY,THURSDAY,FRIDAY,SATURDAY,SUNDAY
}

// print enum
System.out.println(Day.MONDAY);//MONDAY
System.out.println(Day.TUESDAY);//TUESDAY
System.out.println(Day.WEDNESDAY);//WEDNESDAY
System.out.println(Day.TUESDAY);//TUESDAY
System.out.println(Day.FRIDAY);//FRIDAY
System.out.println(Day.SATURDAY);//SATURDAY
System.out.println(Day.SUNDAY);//SUNDAY

// get enum by string

Day day = Day.valueOf("FRIDAY");
System.out.println(day);//FRIDAY
day = Day.valueOf("WRONG");
System.out.println(day);//Exception in thread "main" java.lang.IllegalArgumentException: No enum constant com.company.Day.WRONG

// loop over enum
for (Day day : Day.values()){
    System.out.println(day);
}

// switch by enum
Day day = Day.FRIDAY;
switch (day){
    case MONDAY:
        System.out.println(0);
        break;
    case TUESDAY:
        System.out.println(1);
        break;
    case WEDNESDAY:
        System.out.println(2);
        break;
    case THURSDAY:
        System.out.println(3);
        break;
    case FRIDAY:
        System.out.println(4);
        break;
    case SATURDAY:
        System.out.println(5);
        break;
    case SUNDAY:
        System.out.println(6);
        break;
}

// compare enum
Day day = Day.FRIDAY;
System.out.println(day==Day.FRIDAY);

string

string initialization

length

to lower case and upper case

trim

start with and end with

contains and index of

join and split

• java

// using String.join
String result = String.join("-", "2015", "10", "31" );// 2015-10-31
String result = String.join(", ", list);

// using StringJoiner
StringJoiner sj = new StringJoiner(",");
sj.add("aaa");
sj.add("bbb");
String result = sj.toString(); // aaa,bbb

StringJoiner sj = new StringJoiner("/", "prefix-", "-suffix");
sj.add("2016");
sj.add("02");
String result = sj.toString(); // prefix-2016/02-suffix

// using lambda
String result = list.stream().map(x -> x).collect(Collectors.joining(" | "));

slice the string

compare

title

type conversion

date and time

json

• java gson

/* To use Gson, add following to pom.xml  */
<dependency>
    	<groupId>com.google.code.gson</groupId>
    	<artifactId>gson</artifactId>
    	<version>2.6.2</version>
</dependency>

// Convert java object to json string
User user = new User();
String userInString = new Gson().toJson(user);

// Convert json string to java object
User user = new Gson().from(userInString,User.class);

// Convert json array to java List
String jsonInstring = "[{\"tenant\":\"Google\"}, {\"tenant\":\"Facebook\"}]";
List<Customer> list = gson.fromJson(jsonInString, new TypeToken<List<Customer>>(){}.getType());
list.forEach(x -> System.out.println(x));

// Convert json to java Map
String jsonInstring = "{\"tenant\":\"Google\", \"landscape\":"develop"}";
Map<String, Object> map = gson.fromJson(jsonInString, new TypeToken<Map<String, Object>>(){}.getType());
map.forEach((x,y)-> System.out.println( x + "-" + y));

module

• python

class

errors and exceptions

file IO

• java

// construct a file path
Paths.get(part1,part2,part3,.....)
// create file as well as dirs
Files.createDirectories(scriptPath.getParent());
Files.createFile(scriptPath);
// get a file or dir, create if not exists
File dir = FileUtils.getFile(path);
// delete a directory
FileUtils.deleteDirectory(dir);
// inputstream to file
FileUtils.copyInputStreamToFile(x.getInputStream(), targetFile);

network IO

object oriented programming

object lifecycle

object initialization

memory nodel

reflect

garbage collection

process

thread

format

read from stdin

test

dependency/package management

go

go get -u -v -f all # download all dependencies

maven for java

mvn dependency:tree # check dependency

npm for node.js

npm search db # locate the modules by keywords db
npm install commander@">1.0.0" # greater than version 1.0.0
npm install [email protected] # exactly matches version 1.0.0
npm install commander@"=1.0.0" # exactly matches version 1.0.0
npm install commander@"~1.0.0" # greater than or equal to version 1.0.0 , but less than the mexe major version

npm outdated [module-name] [-g] # display outdated packages [in golbal folder]
npm update [module-name] [-g]  # update outdated packages [in golbal folder]

npm adduser
npm publish

npm ls # view all the m-odules installed in current directory
npm ls -g # view all the modules installed in global directory
npm root -g # view the path that the global modules been installed

npm rm module-name # remove a module

# linking packages is very useful if you are developing a module and want another project to reference your local copy of the module . 
# a linked package can be refered as if it were a global package , 
# which is very similar to module installation . 
#1. create global link
cd my-project & npm link # now your 'my-project' is a global module , you can verify using npm ls -g 
#2. reference an existing link 
cd other-project & npm link my-project # link my-project as a module in your other-project 
#3.unlink package 
cd other-project & npm unlink my-project 
cd my-project & npm unlink