JVM-based basic knowledge of Dynamic Language groovy

In the process of using Java, it is a little more difficult than the C # syntax, such as exceptions and get set. After all, Java has developed a lot longer than C, many problems were not taken into account at the beginning of the design. In order to forward compatibility, we had to keep a certain historical burden (such as generic processing, Java's erasure implementation is the subsequent compatibility considerations ). However, it is very convenient to use groovy grails in a recent project, especially the integration of groovy and Java is very convenient.

The following describes some basic knowledge about groovy for reference. The documentation of groovy itself is also comprehensive, but the length is too long. The following is a concise reference.

Official http://groovy.codehaus.org

Official Website definition: groovy is an agile dynamic language for the Java platform with your features that are supported Red by languages like python, Ruby and smalltalk, making them available to Java developers using a Java-like syntax.

Groovya Dynamic Language made specifically for the JVM.

Groovy was designed with the JVM in mind

Groovy does not just have access to the existing Java API; its groovy development kit (gdk) actually extends the Java API by adding new methods to the existing Java classes tomake them more groovy.

Groovy is a standard governed by the Java Community process (JCP) as Java specification request (JSR) 241.

The following describes the common groovySyntax, according to the usage of this few times, you can quickly get familiar with groovySyntax

1. The default imported namespace is automatic imports	Importjava. Lang .*; Importjava. util .*; Import java.net .*; Import java. Io .*; Import java. Math. biginteger; Import java. Math. bigdecimal; Importgroovy. Lang .*; Importgroovy. util .*; You do not need to introduce interfaces and classes in the above namespace.
2. Optional; semicolon optional semicolons	MSG = "hello" MSG = "hello ";
3. Optional brackets optional parentheses	Println ("Hello world! ") Println "Hello world! " // Method pointer Def pizza = new pizza () Def deliver = pizza. & deliver () Deliver
4. optional return value: Optional return statements	string getfullname () { return" $ {firstname }$ {lastname} " } // equivalent code string getfullname () { " $ {firstname }$ {lastname} " }
5. optional type declaration optional datatype Declaration (duck typing)	S =" hello " def S1 =" hello " string S2 =" hello " printlns. class println s1.class println s2.class
6. Optional Exception Handling optional Exception Handling	// In Java: Try { Reader reader = new filereader ("/foo.txt ") } Catch (filenotfoundexception e ){ E. printstacktrace () } // In GROOVY: Def reader = new filereader ("/foo.txt ")
7. Operator Overloading	Operator Method A = B or! = B a. Equals (B) A + B a. Plus (B) A-B a. Minus (B) A * B a. Multiply (B) A/B A. Div (B) A % B a. Mod (B) A ++ or ++ A. Next () A--or--A. Previous () A & B a. and (B) A | B a. or (B) A [B] A. getat (B) A [B] = c a. putat (B, c) A <B a. leftshift (B) A> B a. rightshift (B) A <B or A> B or a <= B or a> = B a. compareto (B)
8. Safe dereferencing (?)	S = [1, 2] Println s ?. Size () S = NULL Println s ?. Size () Println person ?. Address ?. Phonenumber // optional
9. autoboxing	Autoboxes everything on the specified y Float F = (float) 2.2f F. Class Primitive type automatic packing
10. Groovy truth	// True If (1) // any non-zero value is true If (-1) If (! Null) // any non-null value is true If ("John") // any non-empty string is true Map family = [Dad: "John", MOM: "Jane"] If (family) // true since the map is populated String [] SA = new string [1] If (SA) // true since the array length is greater than 0 Stringbuffersb = new stringbuffer () SB. append ("hi ") If (SB) // true since the stringbuffer is populated // False If (0) // zero is false If (null) // null is false If ("") // empty strings are false Map family = [:] If (family) // false since the map is empty String [] SA = new string [0] If (SA) // false since the array is zero length Stringbuffersb = new stringbuffer () If (SB) // false since the stringbuffer is empty
11. Embedded quotes	Def S1 = 'My name is "Jane "' Def S2 = "My name is 'jar '" Def S3 = "My name is \" Jane \"" Each double quotation mark can represent a string.
12. heredocs (triple quotes)	S = ''' this is Demo ''' Println s Three single and double quotation marks
13. gstrings	Def name = "John" Println "Hello $ {name}. Today is $ {new date ()}"
14. LIST/map shortcuts	Def versions ages = ["Java", "groovy", "jruby"] Printlnages. Class Def array = ["Java", "groovy", "jruby"] as string [] Def set = ["Java", "groovy", "jruby"] as set Def empty = [] Printlnempty. Size () Ages <"Jython" Println ages [1] Printlnages. getat (1) Ages. Each {println it} Ages. Each {Lang-> Printlnlang } Ages. eachwithindex {Lang, I-> Println "$ {I }:$ {Lang }" } Ages. Sort () Ages. Pop () Ages. findall {It. startswith ("G ")} Ages. Collect {It + = "is cool "} // Spread operator (*) Println ages *. touppercase () Def family = [Dad: "John", MOM: "Jane"] Family. Get ("dad ") Printlnfamily. Dad Family. Each {k, V-> Println "$ {v} is the $ {k }" } Family. keyset () Import groovy. SQL. SQL // Spread operator (*) Defparams = [] Params <"JDBC: mysql: // localhost: 3306/test" Params <"root" Params <"" Params <"com. MySQL. JDBC. Driver" Printlnparams Defsql = SQL. newinstance (* Params) // Defdb = [URL: 'jdbc: HSQLDB: Mem: testdb', user: 'sa ', password: '', Driver: 'org. HSQLDB. jdbcdriver'] // Defsql = SQL. newinstance (db. url, DB. User, DB. Password, DB. Driver) Defsql = groovy. SQL. SQL. newinstance ('jdbc: mysql: // localhost: 3306/tekdays ', "root", '', 'com. mySQL. JDBC. driver ') Printlnsql. Connection. Catalog Put the mysql-connector-java-5.0.7-bin.jar In the groovy installation lib directory
15. Ranges	Def r = 1 .. 3 (1 .. 3). Each {println "bye "} Def today = new date () Defnextweek = Today + 7 (Today... nextweek). Each {println it}
16. Closures and blocks	Def HI = {println "hi "} Hi () Def Hello = {println "Hi $ {It }"} Hello ("John ") Defcalculatetax = {taxrate, amount-> Return amount + (taxrate * Amount) } Println "Total Cost :$ {calculatetax (0.055, 100 )}" // Pre-bind Defcalculatetax = {taxrate, amount-> Return amount + (taxrate * Amount) } Def tax = calculatetax. Curry (0.1) [10, 20, 30]. Each { Println "Total Cost :$ {tax (IT )}" }

the length is a little long, but with this knowledge, it is very helpful for the deep use of groovy grails.