creating custom java functions

8/9/2019 creating custom java functions

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Creating Custom Java Functions

Contents

Custom Java Function SamplesCreating Custom Java Simple Functions

Creating Custom Java Aggregate Functions

Method Parameter and Return Types

Related Topics

You can call custom Java functions directly in StreamBase epressions !y an alias defined in the serverconfiguration file" or !y using the calljava() function# The StreamBase epression language provides

t$o forms of thecalljava() function" to !e used in StreamBase simple and aggregate epressions#

This topic provides guidelines for creating StreamBase custom functions in Java#

Note

StreamBase Studio ships $ith ne$ pro%ects configured !y default to !uild $ith Java As ofrelease '#(" Java ) is no longer supported $ithin Studio or for developing Custom *tensions"including Java functions#

Custom Java Function Samples

The StreamBase installation includes the source files for t$o custom Java function samples+

Sample Described in

custom,%ava,function Custom Java Simple Function Sample

custom,%ava,aggregate Custom Java Aggregate Function Sample

Custom aggregate functions are !uilt !y etendingthe com.streambase.sb.operator.AggregateWindow class of the StreamBase Java Client li!rary#

This class is descri!ed in Java AP- .ocumentation#

Creating Custom Java Simple Functions

Simple custom Java functions can !e called in epressions in the contet of most StreamBasecomponents" other than the Aggregate operator# Follo$ these steps to create a custom Java simple

function+

• /se the New StreamBase Java Function $i0ard to create the !ase code" as descri!ed in /sing

the StreamBase Java Function 1i0ard#

• -mplement a public static in a pu!lic Java class#

• 2!serve the guidelines in Method Parameter and Return Types#

For eample" Hypotenuse.java in the sample application declares the follo$ing class and method+

public class Hypotenuse {

public static double calculate(double a, double b) {

return Math.srt(a!a " b!b)# $

$

At compile time" the calljava() implementation loo3s for only a single method matching the eact

types of the function call in the StreamBase epression# But there can !e multiple matching methods"such as these t$o functionally e4uivalent ones+

http://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_sampleshttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_creatingjavasimplehttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_creatingjavaaggregatehttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_javainputsandoutputshttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_relatedtopicshttp://www.streambase.com/developers/docs/latest/reference/sbdxml.html#sbdxml_customfunctionhttp://www.streambase.com/developers/docs/latest/reference/sbdxml.html#sbdxml_customfunctionhttp://www.streambase.com/developers/docs/latest/reference/expressions.html#expressions_calljava_functionhttp://www.streambase.com/developers/docs/latest/reference/expressions.html#expressions_calljava_functionhttp://www.streambase.com/developers/docs/latest/reference/expressions.html#expressions_calljava_functionhttp://www.streambase.com/developers/docs/latest/reference/expressions.html#expressions_aggregatecalljava_functionhttp://www.streambase.com/developers/docs/latest/reference/expressions.html#expressions_aggregatecalljava_functionhttp://www.streambase.com/developers/docs/latest/samplesinfo/Custom_Java_Function.htmlhttp://www.streambase.com/developers/docs/latest/samplesinfo/Custom_Java_Aggregate.htmlhttp://www.streambase.com/developers/docs/latest/apidocs/java/index.htmlhttp://www.streambase.com/developers/docs/latest/apiguide/javafunctionwizd.htmlhttp://www.streambase.com/developers/docs/latest/apiguide/javafunctionwizd.htmlhttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_javainputsandoutputshttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_javainputsandoutputshttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_creatingjavasimplehttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_creatingjavaaggregatehttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_javainputsandoutputshttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_relatedtopicshttp://www.streambase.com/developers/docs/latest/reference/sbdxml.html#sbdxml_customfunctionhttp://www.streambase.com/developers/docs/latest/reference/sbdxml.html#sbdxml_customfunctionhttp://www.streambase.com/developers/docs/latest/reference/expressions.html#expressions_calljava_functionhttp://www.streambase.com/developers/docs/latest/reference/expressions.html#expressions_calljava_functionhttp://www.streambase.com/developers/docs/latest/reference/expressions.html#expressions_aggregatecalljava_functionhttp://www.streambase.com/developers/docs/latest/samplesinfo/Custom_Java_Function.htmlhttp://www.streambase.com/developers/docs/latest/samplesinfo/Custom_Java_Aggregate.htmlhttp://www.streambase.com/developers/docs/latest/apidocs/java/index.htmlhttp://www.streambase.com/developers/docs/latest/apiguide/javafunctionwizd.htmlhttp://www.streambase.com/developers/docs/latest/apiguide/javafunctionwizd.htmlhttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_javainputsandoutputshttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_samples


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public static boolean is%ero(int i) { return i && '# $

public static oolean is%ero(nteger i) {

return i && null * null + oolean.value-(i.intalue() && ')#

$

-f this case occurs" StreamBase thro$s an error#

Creating Custom Java Aggregate Functions

Follo$ these steps to create a custom Java aggregate function+

• /se the New StreamBase Java Function $i0ard to create the !ase code" as descri!ed in /sing

the StreamBase Java Function 1i0ard#

• .efine a Java class that etends

the com.streambase.sb.operator.AggregateWindow class#

• 2!serve the guidelines in Method Parameter and Return Types#

• 2!serve the guidelines in the annotations to the eample !elo$#

Consider the follo$ing annotated eample+

pac/age com.mycompany#

import com.streambase.sb.operator.AggregateWindow#

public class My0tdev e1tends AggregateWindow {

private double sum#

private double sum-0uares#

private int count#

public void init() {

sum & sum-0uares & '.'#

count & '#

$

public double calculate() {

return Math.srt((count ! sum-0uares 2 sum!sum) 3 count!(count24))#

$

public void accumulate(double value) {

sum "& value# sum-0uares "& value!value#

""count#

$

public void release() { 3! nothing to release in this e1ample !3 $

$

The follo$ing annotations descri!e points of interest in the preceding eample+

.eclare a pu!lic class that etends the AggregateWindow class 5as documented in the

StreamBase Java Client li!rary6#

The init() method is called at the start of each ne$ use of the class# Since custom aggregate

o!%ects are li3ely to !e reused" perform all initiali0ation in init() rather than in the

constructor# 5The constructor is called only once" $hile init() is called !efore each use#6

Your implementation must contain a calculate() method that ta3es no arguments and returns

http://www.streambase.com/developers/docs/latest/apiguide/javafunctionwizd.htmlhttp://www.streambase.com/developers/docs/latest/apiguide/javafunctionwizd.htmlhttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_javainputsandoutputshttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_javainputsandoutputshttp://www.streambase.com/developers/docs/latest/apiguide/javafunctionwizd.htmlhttp://www.streambase.com/developers/docs/latest/apiguide/javafunctionwizd.htmlhttp://www.streambase.com/developers/docs/latest/apiguide/customjavafunctions.html#customjavafunctions_javainputsandoutputs


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a value that is converti!le to a StreamBase data type# The calculate() method may !e called

several times" or not at all#

Your implementation must provide at least one accumulate() method" and can optionally

provide several overloaded accumulate() methods" one per data

type# calljava() determines $hich one to call !ased on type# The argument typesfor accumulate() and the return type for calculate() can !e any of the types descri!ed in

the ta!le in the net section#

The release() method is called at the end of each use of the class#

Method Parameter and Return !pes

The method can have any num!er of parameters" including none# *ach parameter must !e a Javaprimitive or o!%ect type corresponding to a StreamBase data type as sho$n in the follo$ing ta!le+

StreamBase Data !pe Java Primitive Java "b#ect

!lo! 7 com#stream!ase#s!#ByteArray8ie$

!ool !oolean %ava#lang#Boolean

dou!le dou!le %ava#lang#.ou!le

int int %ava#lang#-nteger

long long %ava#lang#9ong

list primitive:type;< %ava#util#9ist

string !yte;< %ava#lang#String

timestamp 7 com#stream!ase#s!#Timestamp

tuple 7 com#stream!ase#s!#Tuple

Notes

• For simple functions" the return type cannot !e void" and must !e one of the Java primitive or

Java 2!%ect types sho$n a!ove#

• You can use java.lang.0tring any$here a !yte;< is accepta!le as an argument or return

value# -n this case" the StreamBase string is transparently converted to or froma java.lang.0tring using the system default encoding#

• -f a parameter=s type is !yte;< and its value is null" it is represented as a Java null# 9i3e$ise"

if a Java method $ith a !yte;< return type returns a null" the calling StreamBase epression $illsee the return value as string5null6#

• You can pass a list of lists to functions epecting multi,dimensional array arguments# You can

mi list and array notations $hen doing this# That is" a t$o,dimensional list of dou!les can !epassed to functions accepting any of the follo$ing arguments+

o double5656

o list7double568

o list7list7double88

Note

2nly Java primitive arrays and string arrays are compati!le $ith lists" not comple data typessuch as timestamps or tuples# .ata type coercion is not supported#

Note

1hen an array argument has more than t$o dimensions" you cannot use a function alias# Youmust invo3e the function via calljava()#

• For !etter performance" Java functions can return arrays in place of lists# For eample" the

follo$ing return types are e4uivalent+

• double56 -oo() {$ 33 && list(double)


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• double565656 -oo() {$ 33 && list(list(list(double)))

• -f the parameter or return type is list or tuple" you must either provide a custom function

resolver" or must define the argument types in a custom2-unction element in the server

configuration file# See Custom Functions $ith Comple .ata Types for details#

• -f any value of a parameter $ith a primitive type is null at runtime" the method that

implements the custom function is not invo3ed# >o$ever" Java 2!%ect parameter types can !e usedto pass in null parameter values#

For eample" if a StreamBase custom function call $ould involve converting aStreamBase int(null) or bool(null) value to a primitive Java int or boolean" the method is

not called" and null is assumed as the return value#

public static boolean is%ero(int i) { return i && '# $

calljava(9:he;lass9, 9is%ero9, 4) 3! -alse !

calljava(9:he;lass9, 9is%ero9, ') 3! true !3

calljava(9:he;lass9, 9is%ero9, int(null)) 3! null !3

Related opics• Simple call%ava56 function

• Aggregate call%ava56 function• Java AP- .ocumentation

• Class Aggregate1indo$

• StreamBase Custom Java Function Sample

• StreamBase Custom Java Aggregate Sample

Creating Method:

Considering the following example to explain the syntax of a method:

public static int -unc


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• Functions: They return value.

Method definition consists of a method header and a method body. The same is shown below:

modi-ier return:ype name-Method (=arameter >ist) {

33 method body

$

The syntax shown above includes:

• modifier: It defines the access type of the method and it is optional to use.

• returnType: Method may return a value.

• nameOfMethod: This is the method name. The method signature consists of the method name and the

parameter list.

• Parameter List: The list of parameters, it is the type, order, and number of parameters of a method. These

are optional, method may contain zero parameters.

• method body: The method body defines what the method does with statements.

Example:

Here is the source code of the above defined method called max(). This method takes two parameters num1 and

num2 and returns the maximum between the two:

3!! the snippet returns the minimum between two numbers !3

public static int min?unction(int n4, int n@) {

int min#

i- (n4 8 n@)

min & n@#

else

min & n4#

return min#

$

Method Calling:

For using a method, it should be called. There are two ways in which a method is called i.e. method returns a value or

returning nothing (no return value).

The process of method calling is simple. When a program invokes a method, the program control gets transferred to

the called method. This called method then returns control to the caller in two conditions, when:

• return statement is executed.

• reaches the method ending closing brace.


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The methods returning void is considered as call to a statement. Lets consider an example:

0ystem.out.println(9:his is tutorialspoint.com9)#

The method returning value can be understood by the following example:

int result & sum(B, C)#

Example:

Following is the example to demonstrate how to define a method and how to call it:

public class D1ampleMin


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public class D1ampleoid {

public static void main(0tring56 args) {

methodEan/=oints(@FF.G)#

$

public static void methodEan/=oints(double points) {

i- (points 8& @'@.F) {

0ystem.out.println(9Ean/+A49)#

$

else i- (points 8& 4@@.) {

0ystem.out.println(9Ean/+A@9)#

$

else {

0ystem.out.println(9Ean/+AI9)#

$

$

$

This would produce the following result:

Ean/+A4

Passing Parameters by Value:

While working under calling process, arguments is to be passed. These should be in the same order as their

respective parameters in the method specification. Parameters can be passed by value or by reference.

Passing Parameters by Value means calling a method with a parameter. Through this the argument value is passed to

the parameter.

Example:

The following program shows an example of passing parameter by value. The values of the arguments remains the

same even after the method invocation.

public class swappingD1ample {

public static void main(0tring56 args) {

int a & I'#

int b & F#

0ystem.out.println(9e-ore swapping, a & 9 "

a " 9 and b & 9 " b)#

33 nvo/e the swap method


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swap?unction(a, b)#

0ystem.out.println(9Jn!!


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int result4 & min?unction(a, b)#

33 same -unction name with di--erent parameters

double result@ & min?unction(c, d)#

0ystem.out.println(9Minimum alue & 9 " result4)#

0ystem.out.println(9Minimum alue & 9 " result@)#

$

33 -or integer

public static int min?unction(int n4, int n@) {

int min#

i- (n4 8 n@)

min & n@#

else

min & n4#

return min#

$

33 -or double

public static double min?unction(double n4, double n@) {

double min#

i- (n4 8 n@)

min & n@#

else

min & n4#

return min#

$

$


Minimum alue & B

Minimum alue & G.I

Overloading methods makes program readable. Here, two methods are given same name but with different

parameters. The minimum number from integer and double types is the result.

Using Command-Line Arguments:

Sometimes you will want to pass information into a program when you run it. This is accomplished by passing

command-line arguments to main( ).

A command-line argument is the information that directly follows the program's name on the command line when it is

executed. To access the command-line arguments inside a Java program is quite easy.they are stored as strings in

the String array passed to main( ).


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Example:

The following program displays all of the command-line arguments that it is called with:

public class ;ommand>ine {

public static void main(0tring args56){

-or(int i&'# i7args.length# i""){

0ystem.out.println(9args59 " i " 96+ 9 "

args5i6)#

$

$

$

Try executing this program as shown here:

java ;ommand>ine this is a command line @'' 24''


args5'6+ this

args546+ is

args5@6+ a

args5I6+ command

args56+ line

args5F6+ @''

args5B6+ 24''

The Constructors:

A constructor initializes an object when it is created. It has the same name as its class and is syntactically similar to a

method. However, constructors have no explicit return type.

Typically, you will use a constructor to give initial values to the instance variables defined by the class, or to perform

any other startup procedures required to create a fully formed object.

All classes have constructors, whether you define one or not, because Java automatically provides a default

constructor that initializes all member variables to zero. However, once you define your own constructor, the default

constructor is no longer used.

Example:

Here is a simple example that uses a constructor:

33 A simple constructor.

class My;lass {

int 1#


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33 ?ollowing is the constructor

My;lass() {

1 & 4'#

$

$

You would call constructor to initialize objects as follows:

public class ;onsKemo {

public static void main(0tring args56) {

My;lass t4 & new My;lass()#

My;lass t@ & new My;lass()#

0ystem.out.println(t4.1 " 9 9 " [email protected])#

$

$

Most often, you will need a constructor that accepts one or more parameters. Parameters are added to a constructor

in the same way that they are added to a method, just declare them inside the parentheses after the constructor's

name.

Example:Here is a simple example that uses a constructor:

33 A simple constructor.

class My;lass {

int 1#

33 ?ollowing is the constructor

My;lass(int i ) {

1 & i#

$

$

You would call constructor to initialize objects as follows:

public class ;onsKemo {

public static void main(0tring args56) {

My;lass t4 & new My;lass( 4' )#

My;lass t@ & new My;lass( @' )#

0ystem.out.println(t4.1 " 9 9 " [email protected])#

$

$


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4' @'

Variable Arguments(var-args):JDK 1.5 enables you to pass a variable number of arguments of the same type to a method. The parameter in the

method is declared as follows:

type


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It is possible to define a method that will be called just before an object's final destruction by the garbage collector.

This method is calledfinalize( ), and it can be used to ensure that an object terminates cleanly.

For example, you might use finalize( ) to make sure that an open file owned by that object is closed.

To add a finalizer to a class, you simply define the finalize( ) method. The Java runtime calls that method whenever itis about to recycle an object of that class.

Inside the finalize( ) method, you will specify those actions that must be performed before an object is destroyed.

The finalize( ) method has this general form:

protected void -inaliLe( )

{

33 -inaliLation code here

$

Here, the keyword protected is a specifier that prevents access to finalize( ) by code defined outside its class.

This means that you cannot know when or even if finalize( ) will be executed. For example, if your program ends

before garbage collection occurs, finalize( ) will not execute.

Method Headers

We summarize method headers, define the signature of amethod, and discuss its use. This material is covered in

more detail in the course text, Gries/Gries.

A method declaration consists of a specification (as a

comment, a method header , and a !od". Here is a methoddeclaration#

3!! & 91 is in the range 4..F'9. !3

public boolean is>ess(int 1) {

return 1 8& 4 1 7& F'#

$

Here is the format of the method header $e use in this

class for the three %inds of methods in &ava, giving

information a!out calls on each %ind of method, $ith a fe$notes !elo$#

http://www.cs.cornell.edu/courses/cs1130/2011sp/module2/module2part1/methodHeaders.html#signaturehttp://www.cs.cornell.edu/courses/cs1130/2011sp/module2/module2part1/methodHeaders.html#signature


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'ind of

methodormat of header A call on a method#

procedure public void )name*

( +

s a statement.

function public )return-type* )name*

(

s an expression, $hich "ields a value.

constructo

r

public )class-name*

( ) parameter-list *

Appears in a ne$-expression or as the first

statement of a constructor.

Notes

• 'e"$ord public ma" !e replaced !" private,if "ou $ant the method to !e accessi!le onl" in the class in

$hich it is declared.

• The )name* is an" &ava identifier. onventions for it

are covered !elo$.

•

The )return-type* is the )type* of the valuereturned !" the function. t could !e a primitive t"pe or aclass t"pe.

• The ) parameter-list * contains declarations of the

parameters of the method. t is a (possi!l" empt"

seuence of declarations separated !" commas. 0ach

declaration has the form )type* )variable-name*.

• The )class-name* is the name of the class in $hich

the constructor is declared.

• f the class in $hich this method header appears is

a!stract, then %e"$ord abstract ma" appear after

the access modifier ( public or private. This isexplained in another section.

• or a function or procedure, place

%e"$ord static after the access modifier if the methoddoes not refer directl" to an instance varia!le or instance

method of the class. Then, there $ill !e onl" one cop" of

the method, and it $ill !e placed in the file-dra$er of the

class.

http://www.cs.cornell.edu/courses/cs1130/2011sp/module2/module2part1/methodHeaders.html#nameshttp://www.cs.cornell.edu/courses/cs1130/2011sp/module2/module2part1/methodHeaders.html#names


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Method names

A method name is often $ritten as a seuence of one or

more $ords, li%e to0tring, setess. The first letter of each $ord, except thefirst , is capitalized.

A procedure name is usuall" a command to do something,

e.g. setess(int)

n &ava, the methods in a class must have different

signatures. This means, for example, that one cannot have

!oth a procedure and a function $ith name is>ess and

one int parameter. &ava constrains methods in thisfashion so that, for an" method call, there is no am!iguit"

concerning $hich method is !eing called.


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