groovy & grails - lecture 7

Groovy: Efficiency Oriented Programming
Lecture 7
Master Proteomics & Bioinformatics - University of Geneva
Alexandre Masselot - summer 2011

Contents

‣ Eclipse tips
‣ Productivity tip: back to TDD
‣ Exceptions throwing and catching
‣ reference to object and cloning
‣ OOP: interface

Eclipse tips

‣ STS (Springsource Tool Suite) dashboard:
- keep aware of what is new in the STS environment (new releases, new
plugins, technologies, future webinars...)
- help > dashboard

Eclipse tips

‣ STS (Springsource Tool Suite) dashboard:
- keep aware of what is new in the STS environment (new releases, new
plugins, technologies, future webinars...)
- help > dashboard
‣ Jump directly in junit view
- run junit tests <alt> <shift> X T
- jump to junit window <shift> <alt> Q U
- configure your shortcuts with
preferences > filter “keys” > filter junit
- use multi screen to put console or junit view on the secondary display
(drag the view tab and drop it on the secondary display)

Productivity : TDD

‣ Test Driven Development

Productivity : TDD

‣ Even for a simple task (over 10 lines!)
- write a simple class (in the same directory if you wish)
- split the behavior of your problem into simple methods
- test every method

Productivity : TDD

‣ Even for a simple task (over 10 lines!)
- write a simple class (in the same directory if you wish)
- split the behavior of your problem into simple methods
- test every method

Do not rely on println to
develop/understand your code

Exceptions: using & surviving

6

Exception: example
org.codehaus.groovy.runtime.InvokerInvocationException: groovy.lang.MissingMethodException: No signature of method:
groovy.util.slurpersupport.Attributes.textd() is applicable for argument types: () values: []
Possible solutions: text(), text(), text(), getAt(groovy.lang.IntRange), getAt(int), getAt(java.lang.String)

at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:95)

at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:233)

at groovy.lang.MetaClassImpl.setProperty(MetaClassImpl.java:2395)


at groovy.lang.MetaClassImpl.setProperties(MetaClassImpl.java:1499)

at groovy.lang.MetaClassImpl.invokeConstructor(MetaClassImpl.java:1476)


at org.codehaus.groovy.runtime.InvokerHelper.invokeConstructorOf(InvokerHelper.java:824)

at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.castToType(DefaultTypeTransformation.java:
313)

at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.castToType(ScriptBytecodeAdapter.java:602)

at unige.mpb.eop.proteomics.uniprot.UniprotEntrySplicerTest.setUp(UniprotEntrySplicerTest.groovy:16)

at junit.framework.TestCase.runBare(TestCase.java:128)

at junit.framework.TestResult$1.protect(TestResult.java:106)

at junit.framework.TestResult.runProtected(TestResult.java:124)

at junit.framework.TestResult.run(TestResult.java:109)

at junit.framework.TestCase.run(TestCase.java:120)

at junit.framework.TestSuite.runTest(TestSuite.java:230)

at junit.framework.TestSuite.run(TestSuite.java:225)

at org.eclipse.jdt.internal.junit.runner.junit3.JUnit3TestReference.run(JUnit3TestReference.java:130)

at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)

at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)


at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)

at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: groovy.lang.MissingMethodException: No signature of method: groovy.util.slurpersupport.Attributes.textd()
is applicable for argument types: () values: []

at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.unwrap(ScriptBytecodeAdapter.java:54)

Exception: example









at org.codehaus.groovy.runtime.typehandling.DefaultTypeTransformation.castToType(DefaultTypeTransformation.java:313)


















at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:51)

at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:40)

at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)


at unige.mpb.eop.proteomics.uniprot.UniprotEntrySplicer
$_extractIsoformDescriptors_closure1.doCall(UniprotEntrySplicer.groovy:64)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

at java.lang.reflect.Method.invoke(Method.java:597)



at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:273)

at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:886)

at groovy.lang.Closure.call(Closure.java:276)

at groovy.util.slurpersupport.NodeChildren.find(NodeChildren.java:194)






Exception: example message






























































at
at
at
at
at
junit.framework.TestResult.run(TestResult.java:109)
junit.framework.TestCase.run(TestCase.java:120)
junit.framework.TestSuite.runTest(TestSuite.java:230)
junit.framework.TestSuite.run(TestSuite.java:225)
org.eclipse.jdt.internal.junit.runner.junit3.JUnit3TestReference.run(JUnit3TestReference.java:130)
cause(s) cascade











































at
at
at
at
at
exception name
cause(s) cascade











































at
at
at
at
at
exception name
cause(s) cascade














at
at
at
at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:88)
search for your packages


























at
at
at
at
at
exception name
cause(s) cascade














at
at
at
at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:88)
search for your packages



code line number









Exceptions: surviving & using

‣ In exceptional situations, an event is thrown
def list = ['a', 'b', 'c']
def x = list[-5]


def list = ['a', 'b', 'c']
def x = list[-5]
‣ Output
java.lang.ArrayIndexOutOfBoundsException:
Negative array index [-5] too large for array size 3

at ConsoleScript7.run(ConsoleScript7:3)


def list = ['a', 'b', 'c']
def x = list[-5]
‣ Output
java.lang.ArrayIndexOutOfBoundsException:
Negative array index [-5] too large for array size 3

‣ An exception carries three types of information:

- nature: through it’s class (extends Exception),
- message: detailing the circumstances of the incident
- stack trace: the stack of classes (possibly with line number) to track
where the exception was thrown

Catching exceptions: try / catch

‣ An exception does not mean exiting the program (default behavior)


‣ It is possible to catch an exception
def list = ['10', 'a', '20', '30']
[1, 2, 5, 3, 4].each{ i ->
println "$it"+list[-i].toInteger()
}
println “coincoin”


‣ It is possible to catch an exception impossible!!!
def list = ['10', 'a', '20', '30']
[1, 2, 5, 3, 4].each{ i ->
}


def list = ['10', 'a', '20', '30']
[1, 2, 5, 3, 4].each{ i ->
}
‣ Output
1
30
2
20
java.lang.ArrayIndexOutOfBoundsException: Negative array
index [-5] too large for array size 4

at ConsoleScript17$_run_closure1.doCall(ConsoleScript17:3)

and exit (with code > 0)


def list = ['10', 'a', '20', '30']
[1, 2, 5, 3, 4].each{ i ->
}
‣ Output
1
30 this line is never reached
2
20
java.lang.ArrayIndexOutOfBoundsException: Negative array
index [-5] too large for array size 4

at ConsoleScript17$_run_closure1.doCall(ConsoleScript17:3)

and exit (with code > 0)

(cont’d)

‣ Surround the piece of code you want to secure with try/catch
def list = ['10', 'a', '20', '30']
try{
[1, 2, 5, 3, 4].each{ i ->
}
}catch(Exception e){
println "error: " + e.message
}

(cont’d)

‣ Surround the piece of code you want to secure with try/catch
def list = ['10', 'a', '20', '30']
try{
[1, 2, 5, 3, 4].each{ i ->
}
}
‣ Output
1
30
2
20
error: Negative array index [-5] too large for array size 4
coincoin

(cont’d)

def list = ['10', 'a', '20', '30']
try{
[1, 2, 5, 3, 4].each{ i ->
}
}

(cont’d)

def list = ['10', 'a', '20', '30']
try{
[1, 2, 5, 3, 4].each{ i ->
}
}catch(Exception e){ exit the loop
}

Goal: catch exceptions but continue the loop

13

(cont’d)

‣ Adapt the depth of catching

(cont’d)

‣ In the following case, the iteration will continue after an exception is caught
def list = ['10', 'a', '20', '30']
[1, 2, 5, 3, 4].each{ i ->
try{
println "error with ($i): "+e.message
}
}

(cont’d)

‣ In the following case, the iteration will continue after an exception is caught
def list = ['10', 'a', '20', '30']
[1, 2, 5, 3, 4].each{ i ->
try{
}
}
‣ Output
1
30
2
20
error with (5): Negative array index [-5] too large for array size 4
error with (3): For input string: "a"
4
10

catch(Exception e)
is generic (all exceptions are caught)

15

Goal: catch specific exceptions

16

(cont’d)

‣ You can catch only certain classes of Exception
def list = ['10', 'a', '20', '30']
[1, 2, 5, 3, 4].each{ i ->
try{
}catch(ArrayIndexOutOfBoundsException e){
}
}

(cont’d)

‣ You can catch only certain classes of Exception
def list = ['10', 'a', '20', '30']
[1, 2, 5, 3, 4].each{ i ->
try{
}
}

‣ Output
1
30
2
20
error with (5): Negative array index [-5] too large for
array size 4
+ unrecovered stack trace and exit because of
java.lang.NumberFormatException
=> code exits

(cont’d)

‣ Or even cascade catching
def list = ['10', 'a', '20', '30']
[1, 2, 5, 3, 4].each{ i ->
try{
println "out of bound!"
}catch(NumberFormatException e){
println "cannot to convert '${list[-i]}' to int"
}
}

(cont’d)

‣ Or even cascade catching
def list = ['10', 'a', '20', '30']
[1, 2, 5, 3, 4].each{ i ->
try{
println "out of bound!"
}catch(NumberFormatException e){
println "cannot to convert '${list[-i]}' to int"
}
}
‣ Output
1
30
2
20
out of bound!
cannot to convert 'a' to int
4
10

Throwing your Exception

‣ In some situation, it is powerful to throw an exception in your code (to be
hopefully caught at a meaningful place...)


‣ Example:
- you are in the third level of nested function when some illegal action happens,
- you do not want to manage all the return statements of your functions up to
the place where the high level action is to be undertaken
- you want to carry a meaningful message


‣ Example:
- you are in the third level of nested function when some illegal action happens,
- you do not want to manage all the return statements of your functions up to
the place where the high level action is to be undertaken
- you want to carry a meaningful message
‣ Example
int factorial(int n){
if(n<0)
throw new RuntimeException(“cannot pass negative value
($n)”)
//continue
}


if(n<0)
($n)”)
//continue
}
def computeFactorial(int n){
if(n>100)
return -1
factorial(n)
}
//Script
try{
computeFactorial(i)
}catch(Exception e){....}


if(n<0)
($n)”)
//continue
}
def computeFactorial(int n){
if(n>100)
throw new IllegalArgumentException(“no fact for >100”)
factorial(n)
}
//Script
try{
computeFactorial(i)
}catch(Exception e){....}


‣ You code is more clear & robust:
- 10 lines per function limits complex if / else construct.


‣ Document the exception that can be thrown in your function header
comment
/**
...
@Throws RuntimeException if argument is negative
*/


comment
/**
...
*/
‣ Make the message meaningful.


comment
/**
...
*/
‣ Make the message meaningful.
‣ You can create your own Exception class that extends whatever existing
Exception:

- to have generic behavior or catch only your own exception.

Copying an Object

‣ We want to copy a list, then modify its copy without altering the original
def l_1 = ('a'..'e').toList()
def l_2 = l_1

l_2[2] = 'Z'
println "l_1t$l_1"
println "l_2t$l_2"

Copying an Object

def l_2 = l_1

l_2[2] = 'Z'
println "l_1t$l_1"
println "l_2t$l_2"
‣ Output
l_1
[a, b, Z, d, e] // arghhh! we have a ‘Z’ in l_1
l_2
[a, b, Z, d, e]

Copying an Object

def l_2 = l_1

l_2[2] = 'Z'
println "l_1t$l_1"
println "l_2t$l_2"
‣ Output
l_1
l_2
[a, b, Z, d, e]
‣ We do not copy all elements of l_1 to l_2, but rather let l_2 be a
reference to the same Object as l_1

Copying an Object

def l_2 = l_1

l_2[2] = 'Z'
println "l_1t$l_1"
println "l_2t$l_2"
‣ Output
l_1
l_2
[a, b, Z, d, e]

‣ Modifying l_1 modifies l_2 as a side effect

Copying an Object

def l_2 = l_1

l_2[2] = 'Z'
println "l_1t$l_1"
println "l_2t$l_2"
‣ Output
l_1
l_2
[a, b, Z, d, e]

‣ Modifying l_1 modifies l_2 as a side effect
‣ This feature can be meaningful (memory, consistency...)

Cloning an Object: o.clone()

‣ The solution is to explicitly clone the object
def l_2 = l_1.clone()
l_2[2] = 'Z'
println "l_1t$l_1"
println "l_2t$l_2"


l_2[2] = 'Z'
println "l_1t$l_1"
println "l_2t$l_2"
‣ Output
l_1
[a, b, c, d, e]
l_2
[a, b, Z, d, e]


l_2[2] = 'Z'
println "l_1t$l_1"
println "l_2t$l_2"
‣ Output
l_1
[a, b, c, d, e]
l_2
[a, b, Z, d, e]
‣ l_1 is effectively duplicated: further modifications on l_2 do not alter l_1

Cloning an Object (cont’d)

‣ The same applies to a class
class Foo{
String name
List values
}
Foo f_1=[name:'donald', values:[1,2,3]]
Foo f_2=f_1
f_2.name='mickey'

println "f_1t$f_1.namet$f_1.values"


‣ The same applies to a class
class Foo{
String name
List values
}
Foo f_2=f_1
f_2.name='mickey'

‣ Output
f_1
mickey
[1, 2, 3]
f_2
mickey
[1, 2, 3]


‣ If we try
f_2 = f_1.clone()
‣ We obtain
java.lang.CloneNotSupportedException: Foo


We need to define what we mean by cloneable

27


‣ The class Foo must implements an interface Cloneable
class Foo implements Cloneable{
String name
List values

Foo clone(){
return new Foo(‘name’: name, ‘values’: values.clone())
} //explicitly duplicate all fields
}


‣ We can now safely clone
Foo f_2=f_1.clone()

f_2.name='mickey'
f_2.values[1] = 9



‣ We can now safely clone
Foo f_2=f_1.clone()

f_2.name='mickey'
f_2.values[1] = 9

‣ Output
f_1
donald
[1, 2, 3]
f_2
mickey
[1, 9, 3]

OOP : Interface

‣ An interface is a manner to specify what behavior(s) a class should
have, without writing any specific code

OOP : Interface

‣ An interface is a manner to specify what behavior(s) a class should
have, without writing any specific code
‣ A class later implements the interface, thus it is enforced to fulfill the
mentioned mechanism

How to make a class enforce a behavior?

31

Interface examples

‣ Two examples we already met

Interface examples

‣ objects can be compared with <, <=, == etc.
class MyClass implements Comparable{
...
int compareTo(o){
...
}
}

Interface examples

‣ objects can be compared with <, <=, == etc.
class MyClass implements Comparable{
...
int compareTo(o){
...
}
}
‣ objects can be duplicated safely
class MyClass implements Cloneable{
...
MyClass clone(){
...
}
}

Interface examples

‣ They can be combined

Interface examples

‣ They can be combined
‣ objects can be compared and cloned
class MyClass implements Comparable, Cloneable{
...
int compareTo(o){
...
}
MyClass clone(){
...
}
}

How to define an interface?

34

Interface definition

‣ Like a class file (class is replaced by interface)


‣ There is no execution code inside the file (on specification)


‣ There is no execution code inside the file (on specification)
‣ File HasSequence.groovy
interface HasSequence{
String getSequence();
String fastaString();
}


‣ class file then need to implements those two methods Protein.groovy
class Protein implements HasSequence{
String accessionCode
String sequence //getSequence() will be automatically
//defined

String fastaString(){
“>$accessionCoden$sequencen”
}
}

Interface versus Abstraction

interface MyInterface {...}
abstract class MyAbstractClass{...}


‣ Syntax
class MyClass implements MyInterface{...}
class MyClass extends MyAbstractClass{...}


‣ Syntax
‣ interface cannot contains explicit code (only specifications)


‣ Syntax
‣ abstract class contains explicit code (see AminoAcidSequence), but can
also contain abstract methods (to be implemented by children classes)


‣ Syntax
‣ abstract class contains explicit code (see AminoAcidSequence), but can
also contain abstract methods (to be implemented by children classes)
‣ A class can implements several interfaces, but only one abstract parent


‣ Dynamic typing in groovy => interfaces not as important as in java


‣ Dynamic typing in groovy => interfaces not as important as in java
‣ Strengthen the code readability and safety
List<HasSequence> ....

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