![Git Cheat Sheet
Create a Repository
From scratch -- Create a new local
repository
$ git init [project name]
Download from an existing repository
$ git clone my_url
Synchronize
Make a change
Observe your Repository
List new or modified files not yet
committed
$ git status
Show the changes to files not yet staged
$ git diff
Show the changes to staged files
$ git diff --cached
Show all staged and unstaged
file changes
$ git diff HEAD
Show the changes between two
commit ids
$ git diff commit1 commit2
List the change dates and authors
for a file
$ git blame [file]
Show the file changes for a commit
id and/or file
$ git show [commit]:[file]
Show full change history
$ git log
Show change history for file/directory
including diffs
$ git log -p [file/directory]
Stages the file, ready for commit
$ git add [file]
Stage all changed files, ready for commit
$ git add .
Commit all staged files to versioned history
$ git commit -m “commit message”
Commit all your tracked files to
versioned history
$ git commit -am “commit message”
Unstages file, keeping the file changes
$ git reset [file]
Revert everything to the last commit
$ git reset --hard
Get the latest changes from origin
(no merge)
$ git fetch
Fetch the latest changes from origin
and merge
$ git pull
Fetch the latest changes from origin
and rebase
$ git pull --rebase
Push local changes to the origin
$ git push
Working with Branches
List all local branches
$ git branch
List all branches, local and remote
$ git branch -av
Switch to a branch, my_branch,
and update working directory
$ git checkout my_branch
Create a new branch called new_branch
$ git branch new_branch
Delete the branch called my_branch
$ git branch -d my_branch
Merge branch_a into branch_b
$ git checkout branch_b
$ git merge branch_a
Tag the current commit
$ git tag my_tag
Finally!
When in doubt, use git help
$ git command --help
Or visit https://training.github.com/
for official GitHub training.
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![Regex cheat sheet
Character classes
[abc] matches a or b, or c.
[^abc] negation, matches everything except a, b, or c.
[a-c] range, matches a or b, or c.
[a-c[f-h]] union, matches a, b, c, f, g, h.
[a-c&&[b-c]] intersection, matches b or c.
[a-c&&[^b-c]]
subtraction, matches a.
Useful Java classes & methods
PATTERN
A pattern is a compiler representation of a regular expression.
Pattern compile(String regex)
Compiles the given regular expression into a pattern.
Pattern compile(String regex, int flags)
Compiles the given regular expression into a pattern
with the given flags.
boolean matches(String regex)
Tells whether or not this string matches the given
regular expression.
String[] split(CharSequence input)
Splits the given input sequence around matches of
this pattern.
String quote(String s)
Returns a literal pattern String for the specified String.
Predicate<String> asPredicate()
Creates a predicate which can be used to match a string.
Predefined character classes
. Any character.
d A digit: [0-9]
D A non-digit: [^0-9]
s A whitespace character: [ tnx0Bfr]
S A non-whitespace character: [^s]
w A word character: [a-zA-Z_0-9]
W A non-word character: [^w]
Boundary matches
^ The beginning of a line.
$ The end of a line.
b A word boundary.
B A non-word boundary.
A The beginning of the input.
G The end of the previous match.
Z The end of the input but for the final terminator, if any.
z The end of the input.
MATCHER
An engine that performs match operations on a character
sequence by interpreting a Pattern.
boolean matches()
Attempts to match the entire region against the pattern.
boolean find()
Attempts to find the next subsequence of the input
sequence that matches the pattern.
int start()
Returns the start index of the previous match.
int end()
Returns the offset after the last character matched.
Logical operations
XY X then Y.
X|Y X or Y.
Greedy - matches the longest matching group.
Reluctant - matches the shortest group.
Possessive - longest match or bust (no backoff).
Greedy Reluctant Possessive Description
X? X?? X?+ X, once or not at all.
X* X*? X*+ X, zero or more times.
X+ X+? X++ X, one or more times.
X{n} X{n}? X{n}+ X, exactly n times.
X{n,} X{n,}? X{n,}+ X, at least n times.
X{n,m} X{n,m}? X{n,m}+
X, at least n but
not more than m times.
Groups & backreferences
A group is a captured subsequence of characters which may
be used later in the expression with a backreference.
(...) - defines a group.
N - refers to a matched group.
(dd) - a group of two digits.
(dd)/1- two digits repeated twice.
1 - refers to the matched group.
Pattern flags
Pattern.CASE_INSENSITIVE - enables case-insensitive
matching.
Pattern.COMMENTS - whitespace and comments starting
with # are ignored until the end of a line.
Pattern.MULTILINE - one expression can match
multiple lines.
Pattern.UNIX_LINES - only the 'n' line terminator
is recognized in the behavior of ., ^, and $.
Quantifiers
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cheat-sheets.pdf
- 1. Cheat Sheets! MUST-HAVE CHEAT SHEETS FOR JAVA DEVELOPERS CONCISE, HELPFUL, BEAUTIFUL, PRINTABLE by Z E R O T U R N A R O U N D by Z E R O T U R N A R O U N D
- 2. Java 8 Streams Cheat Sheet Definitions A stream is a pipeline of functions that can be evaluated. Streams can transform data. A stream is not a data structure. Streams cannot mutate data. Terminal operations . Return concrete types or produce a side effect. . Eagerly executed. Function Output When to use reduce concrete type to cumulate elements collect list, map or set to group elements forEach side effect to perform a side effect on elements Common examples include: Stream examples Get the unique surnames in uppercase of the first 15 book authors that are 50 years old or over. library.stream() .map(book -> book.getAuthor()) .filter(author -> author.getAge() >= 50) .distinct() .limit(15) .map(Author::getSurname) .map(String::toUpperCase) .collect(toList()); Compute the sum of ages of all female authors younger than 25. library.stream() .map(Book::getAuthor) .filter(a -> a.getGender() == Gender.FEMALE) .map(Author::getAge) .filter(age -> age < 25) .reduce(0, Integer::sum): Parallel streams Parallel streams use the common ForkJoinPool for threading. library.parallelStream()... or intermediate operation: IntStream.range(1, 10).parallel()... Useful operations Grouping: library.stream().collect( groupingBy(Book::getGenre)); Stream ranges: IntStream.range(0, 20)... Infinite streams: IntStream.iterate(0, e -> e + 1)... Max/Min: IntStream.range(1, 10).max(); FlatMap: twitterList.stream() .map(member -> member.getFollowers()) .flatMap(followers -> followers.stream()) .collect(toList()); Pitfalls Avoid blocking operations when using parallel streams. Don’t update shared mutable variables i.e. List<Book> myList = new ArrayList<>(); library.stream().forEach (e -> myList.add(e)); Intermediate operations . Always return streams. Function Preserves count Preserves type Preserves order map filter distinct sorted peek Common examples include: . Lazily executed. BROUGHT TO YOU BY
- 3. How fast are your collections? Collection class Random access by index / key Search / Contains Insert Remember, not all operations are equally fast. Here’s a reminder of how to treat the Big-O complexity notation: O(1) - constant time, really fast, doesn’t depend on the size of your collection O(log(n)) - pretty fast, your collection size has to be extreme to notice a performance impact O(n) - linear to your collection size: the larger your collection is, the slower your operations will be ArrayList O(1) O(n) O(n) HashSet O(1) O(1) O(1) HashMap O(1) O(1) O(1) TreeMap O(log(n)) O(log(n)) O(log(n)) Java Collections Cheat Sheet Notable Java collections libraries Fastutil http://fastutil.di.unimi.it/ Fast & compact type-specific collections for Java Great default choice for collections of primitive types, like int or long. Also handles big collections with more than 231 elements well. Guava https://github.com/google/guava Google Core Libraries for Java 6+ Perhaps the default collection library for Java projects. Contains a magnitude of convenient methods for creating collection, like fluent builders, as well as advanced collection types. Eclipse Collections https://www.eclipse.org/collections/ Features you want with the collections you need Previously known as gs-collections, this library includes almost any collection you might need: primitive type collections, multimaps, bidirectional maps and so on. JCTools https://github.com/JCTools/JCTools Java Concurrency Tools for the JVM. If you work on high throughput concurrent applications and need a way to increase your performance, check out JCTools. What can your collection do for you? Collection class Thread-safe alternative Your data Operations on your collections Individual elements Key-value pairs Duplicate element support Primitive support Order of iteration Performant ‘contains’ check Random access FIFO Sorted LIFO By key By value By index HashMap ConcurrentHashMap HashBiMap (Guava) Maps.synchronizedBiMap (new HashBiMap()) ArrayListMultimap (Guava) Maps.synchronizedMultiMap (new ArrayListMultimap()) LinkedHashMap Collections.synchronizedMap (new LinkedHashMap()) TreeMap ConcurrentSkipListMap Int2IntMap (Fastutil) ArrayList CopyOnWriteArrayList HashSet Collections.newSetFromMap (new ConcurrentHashMap<>()) IntArrayList (Fastutil) PriorityQueue PriorityBlockingQueue ArrayDeque ArrayBlockingQueue * O(log(n)) complexity, while all others are O(1) - constant time ** when using Queue interface methods: offer() / poll() * ** * ** ** BROUGHT TO YOU BY
- 4. Git Cheat Sheet Create a Repository From scratch -- Create a new local repository $ git init [project name] Download from an existing repository $ git clone my_url Synchronize Make a change Observe your Repository List new or modified files not yet committed $ git status Show the changes to files not yet staged $ git diff Show the changes to staged files $ git diff --cached Show all staged and unstaged file changes $ git diff HEAD Show the changes between two commit ids $ git diff commit1 commit2 List the change dates and authors for a file $ git blame [file] Show the file changes for a commit id and/or file $ git show [commit]:[file] Show full change history $ git log Show change history for file/directory including diffs $ git log -p [file/directory] Stages the file, ready for commit $ git add [file] Stage all changed files, ready for commit $ git add . Commit all staged files to versioned history $ git commit -m “commit message” Commit all your tracked files to versioned history $ git commit -am “commit message” Unstages file, keeping the file changes $ git reset [file] Revert everything to the last commit $ git reset --hard Get the latest changes from origin (no merge) $ git fetch Fetch the latest changes from origin and merge $ git pull Fetch the latest changes from origin and rebase $ git pull --rebase Push local changes to the origin $ git push Working with Branches List all local branches $ git branch List all branches, local and remote $ git branch -av Switch to a branch, my_branch, and update working directory $ git checkout my_branch Create a new branch called new_branch $ git branch new_branch Delete the branch called my_branch $ git branch -d my_branch Merge branch_a into branch_b $ git checkout branch_b $ git merge branch_a Tag the current commit $ git tag my_tag Finally! When in doubt, use git help $ git command --help Or visit https://training.github.com/ for official GitHub training. BROUGHT TO YOU BY
- 5. cheat sheet Getting started with Maven Useful command line options -DskipTests=true compiles the tests, but skips running them -Dmaven.test.skip=true skips compiling the tests and does not run them -T - number of threads: -T 4 is a decent default -T 2C - 2 threads per CPU -rf, --resume-from resume build from the specified project -pl, --projects makes Maven build only specified modules and not the whole project -am, --also-make makes Maven figure out what modules out target depends on and build them too -o, --offline work offline -X, --debug enable debug output -P, --activate-profiles comma-delimited list of profiles to activate -U, --update-snapshots forces a check for updated dependencies on remote repositories -ff, --fail-fast stop at first failure Create Java project mvn archetype:generate -DgroupId=org.yourcompany.project -DartifactId=application Create web project mvn archetype:generate -DgroupId=org.yourcompany.project -DartifactId=application -DarchetypeArtifactId=maven-archetype-webapp Create archetype from existing project mvn archetype:create-from-project Main phases clean — delete target directory validate — validate, if the project is correct compile — compile source code, classes stored in target/classes test — run tests package — take the compiled code and package it in its distributable format, e.g. JAR, WAR verify — run any checks to verify the package is valid and meets quality criteria install — install the package into the local repository deploy — copies the final package to the remote repository Help plugin — used to get relative information about a project or the system. mvn help:describe describes the attributes of a plugin mvn help:effective-pom displays the effective POM as an XML for the current build, with the active profiles factored in. Dependency plugin — provides the capability to manipulate artifacts. mvn dependency:analyze analyzes the dependencies of this project mvn dependency:tree prints a tree of dependencies Compiler plugin — compiles your java code. Set language level with the following configuration: <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</ artifactId> <version>3.6.1</version> <configuration> <source>1.8</source> <target>1.8</target> </configuration> </plugin> Version plugin — used when you want to manage the versions of artifacts in a project's POM. Wrapper plugin — an easy way to ensure a user of your Maven build has everything that is necessary. Spring Boot plugin — compiles your Spring Boot app, build an executable fat jar. Exec — amazing general purpose plugin, Essential plugins Central Plugins Dependencies ~/.m2/settings.xml Local Repository compile test package maven-compiler-plugin compiler:compile maven-jar-plugin jar:jar BROUGHT TO YOU BY
- 6. SQL cheat sheet Basic Queries Views -- filter your columns SELECT col1, col2, col3, ... FROM table1 -- filter the rows WHERE col4 = 1 AND col5 = 2 -- aggregate the data GROUP by … -- limit aggregated data HAVING count(*) > 1 -- order of the results ORDER BY col2 Useful keywords for SELECTS: DISTINCT - return unique results BETWEEN a AND b - limit the range, the values can be numbers, text, or dates LIKE - pattern search within the column text IN (a, b, c) - check if the value is contained among given. Data Modification -- update specific data with the WHERE clause UPDATE table1 SET col1 = 1 WHERE col2 = 2 -- insert values manually INSERT INTO table1 (ID, FIRST_NAME, LAST_NAME) VALUES (1, ‘Rebel’, ‘Labs’); -- or by using the results of a query INSERT INTO table1 (ID, FIRST_NAME, LAST_NAME) SELECT id, last_name, first_name FROM table2 A VIEW is a virtual table, which is a result of a query. They can be used to create virtual tables of complex queries. CREATE VIEW view1 AS SELECT col1, col2 FROM table1 WHERE … The Joy of JOINs A B A B RIGHT OUTER JOIN - all rows from table B, even if they do not exist in table A INNER JOIN - fetch the results that exist in both tables LEFT OUTER JOIN - all rows from table A, even if they do not exist in table B Updates on JOINed Queries You can use JOINs in your UPDATEs UPDATE t1 SET a = 1 FROM table1 t1 JOIN table2 t2 ON t1.id = t2.t1_id WHERE t1.col1 = 0 AND t2.col2 IS NULL; NB! Use database specific syntax, it might be faster! Semi JOINs You can use subqueries instead of JOINs: SELECT col1, col2 FROM table1 WHERE id IN (SELECT t1_id FROM table2 WHERE date > CURRENT_TIMESTAMP) Indexes If you query by a column, index it! CREATE INDEX index1 ON table1 (col1) Don’t forget: Avoid overlapping indexes Avoid indexing on too many columns Indexes can speed up DELETE and UPDATE operations Reporting Use aggregation functions COUNT - return the number of rows SUM - cumulate the values AVG - return the average for the group MIN / MAX - smallest / largest value Useful Utility Functions -- convert strings to dates: TO_DATE (Oracle, PostgreSQL), STR_TO_DATE (MySQL) -- return the first non-NULL argument: COALESCE (col1, col2, “default value”) -- return current time: CURRENT_TIMESTAMP -- compute set operations on two result sets SELECT col1, col2 FROM table1 UNION / EXCEPT / INTERSECT SELECT col3, col4 FROM table2; Union - returns data from both queries Except - rows from the first query that are not present in the second query Intersect - rows that are returned from both queries BROUGHT TO YOU BY
- 7. Regex cheat sheet Character classes [abc] matches a or b, or c. [^abc] negation, matches everything except a, b, or c. [a-c] range, matches a or b, or c. [a-c[f-h]] union, matches a, b, c, f, g, h. [a-c&&[b-c]] intersection, matches b or c. [a-c&&[^b-c]] subtraction, matches a. Useful Java classes & methods PATTERN A pattern is a compiler representation of a regular expression. Pattern compile(String regex) Compiles the given regular expression into a pattern. Pattern compile(String regex, int flags) Compiles the given regular expression into a pattern with the given flags. boolean matches(String regex) Tells whether or not this string matches the given regular expression. String[] split(CharSequence input) Splits the given input sequence around matches of this pattern. String quote(String s) Returns a literal pattern String for the specified String. Predicate<String> asPredicate() Creates a predicate which can be used to match a string. Predefined character classes . Any character. d A digit: [0-9] D A non-digit: [^0-9] s A whitespace character: [ tnx0Bfr] S A non-whitespace character: [^s] w A word character: [a-zA-Z_0-9] W A non-word character: [^w] Boundary matches ^ The beginning of a line. $ The end of a line. b A word boundary. B A non-word boundary. A The beginning of the input. G The end of the previous match. Z The end of the input but for the final terminator, if any. z The end of the input. MATCHER An engine that performs match operations on a character sequence by interpreting a Pattern. boolean matches() Attempts to match the entire region against the pattern. boolean find() Attempts to find the next subsequence of the input sequence that matches the pattern. int start() Returns the start index of the previous match. int end() Returns the offset after the last character matched. Logical operations XY X then Y. X|Y X or Y. Greedy - matches the longest matching group. Reluctant - matches the shortest group. Possessive - longest match or bust (no backoff). Greedy Reluctant Possessive Description X? X?? X?+ X, once or not at all. X* X*? X*+ X, zero or more times. X+ X+? X++ X, one or more times. X{n} X{n}? X{n}+ X, exactly n times. X{n,} X{n,}? X{n,}+ X, at least n times. X{n,m} X{n,m}? X{n,m}+ X, at least n but not more than m times. Groups & backreferences A group is a captured subsequence of characters which may be used later in the expression with a backreference. (...) - defines a group. N - refers to a matched group. (dd) - a group of two digits. (dd)/1- two digits repeated twice. 1 - refers to the matched group. Pattern flags Pattern.CASE_INSENSITIVE - enables case-insensitive matching. Pattern.COMMENTS - whitespace and comments starting with # are ignored until the end of a line. Pattern.MULTILINE - one expression can match multiple lines. Pattern.UNIX_LINES - only the 'n' line terminator is recognized in the behavior of ., ^, and $. Quantifiers BROUGHT TO YOU BY