Why method A is not compiled while methods B and C are ok?
class A {
methodA() {
}
void methodB() {
}
static methodC() {
}
}
You need to use the "def" modifier in groovy if you are not declaring a type for the method:
class A {
def methodA() {
}
}
should work.
Related
I have the following code. I have an abstract JobParams, a class extending that abstract GradleJobParams, and a gjp variable with value using anonymous class declaration.
I want to test the overriding behavior of groovy. I can override the method setupRoot() but not the property testVar, why is that?
Tested on: https://groovyconsole.appspot.com/script/5146436232544256
abstract class JobParams {
int root
def testVar=1
def setupRoot () {
println("The root");
}
def printTestVar () {
println("The testVar:" + testVar);
}
}
class GradleJobParams extends JobParams {
}
def gjp = [
testVar:3,
setupRoot:{
println("Override root");
}
] as GradleJobParams;
println("Starting");
gjp.printTestVar();
gjp.setupRoot();
The result is:
Starting
The testVar:1
Override root
Java (and thus Groovy) does not support overriding fields from the parent class with subclassing. Instead, it uses a mechanism called hiding fields:
Hiding Fields
Within a class, a field that has the same name as a field in the superclass hides the superclass's field, even if their types are different. Within the subclass, the field in the superclass cannot be referenced by its simple name. Instead, the field must be accessed through super, which is covered in the next section. Generally speaking, we don't recommend hiding fields as it makes code difficult to read.
Source: https://docs.oracle.com/javase/tutorial/java/IandI/hidevariables.html
It can be simply illustrated with the following example in Java:
final class SubclassHiddingFieldExample {
static abstract class A {
int value = 10;
void printValue1() {
System.out.println(value);
}
void printValue2() {
System.out.println(this.value);
}
void printValue3() {
System.out.println(((B)this).value);
}
}
static class B extends A {
int value = 12;
}
public static void main(String[] args) {
final B b = new B();
b.printValue1();
b.printValue2();
b.printValue3();
}
}
Output:
10
10
12
As you can see, only printValue3 prints out 3, because it cast this explicitly to B class.
Now, if you look at the decompiled bytecode of your JobParams class, you can see that the printTestVar method code is an equivalent of the following Java code:
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
import groovy.lang.GroovyObject;
import groovy.lang.MetaClass;
import org.codehaus.groovy.runtime.callsite.CallSite;
public abstract class JobParams implements GroovyObject {
private int root;
private Object testVar;
public JobParams() {
CallSite[] var1 = $getCallSiteArray();
byte var2 = 1;
this.testVar = Integer.valueOf(var2);
MetaClass var3 = this.$getStaticMetaClass();
this.metaClass = var3;
}
public Object setupRoot() {
CallSite[] var1 = $getCallSiteArray();
return var1[0].callCurrent(this, "The root");
}
public Object printTestVar() {
CallSite[] var1 = $getCallSiteArray();
return var1[1].callCurrent(this, var1[2].call("The testVar:", this.testVar));
}
public MetaClass getMetaClass() {
MetaClass var10000 = this.metaClass;
if (var10000 != null) {
return var10000;
} else {
this.metaClass = this.$getStaticMetaClass();
return this.metaClass;
}
}
public void setMetaClass(MetaClass var1) {
this.metaClass = var1;
}
public Object invokeMethod(String var1, Object var2) {
return this.getMetaClass().invokeMethod(this, var1, var2);
}
public Object getProperty(String var1) {
return this.getMetaClass().getProperty(this, var1);
}
public void setProperty(String var1, Object var2) {
this.getMetaClass().setProperty(this, var1, var2);
}
public int getRoot() {
return this.root;
}
public void setRoot(int var1) {
this.root = var1;
}
public Object getTestVar() {
return this.testVar;
}
public void setTestVar(Object var1) {
this.testVar = var1;
}
}
You can see that the line that prints out the value of the testVar field is represented by:
return var1[1].callCurrent(this, var1[2].call("The testVar:", this.testVar));
It means that no matter what value of testVar your subclass defines, the printTestVar method uses testVar field defined in the JobParams class. Period.
Using Groovy auto getter methods
There is one way you to implement the expected behavior. Every class field in Groovy has a getter method associated with that field compiled by Groovy for you. It means that you can access testVar by calling the getTestVar() method generated by the Groovy compiler. You can use it to override the value returned by a getter method for any field from the subclass. Consider the following example:
abstract class JobParams {
int root
def testVar=1
def setupRoot () {
println("The root");
}
def printTestVar () {
println("The testVar:" + getTestVar()); // <-- using a getTestVar() method instead a testVar field
}
}
class GradleJobParams extends JobParams {
}
def gjp = [
getTestVar: 3, // <-- stubbing getTestVar() method to return a different value
setupRoot:{
println("Override root");
}
] as GradleJobParams;
println("Starting");
gjp.printTestVar();
gjp.setupRoot();
Output:
Starting
The testVar:3
Override root
Is threre any way to ues override method in anonymous class on Groovy #CompileStatic annotation?
groogy source
import groovy.transform.CompileStatic;
interface HelloWorld {
public void greet();
}
class HelloWorldAnonymousClassesParents {
public void hi() {
println "hi"
}
}
#CompileStatic
public class HelloWorldAnonymousClasses extends HelloWorldAnonymousClassesParents {
public void hi() {
System.out.println("hihi ");
}
public void sayHello() {
HelloWorld spanishGreeting = new HelloWorld() {
public void greet() {
hi() //<- here [Static type checking] - Reference to method is ambiguous error
System.out.println("spanishGreeting");
}
};
spanishGreeting.greet();
hi()
}
}
def myApp = new HelloWorldAnonymousClasses();
myApp.sayHello();
Same source in java run well
java source
package org.octopus;
class HelloWorldAnonymousClassesParents {
public void hi() {
System.out.println("hi ");
}
}
interface HelloWorld {
public void greet();
}
public class Test extends HelloWorldAnonymousClassesParents{
public void hi() {
System.out.println("hihi ");
}
public void sayHello() {
HelloWorld spanishGreeting = new HelloWorld() {
public void greet() {
hi();
System.out.println("spanishGreeting");
}
};
spanishGreeting.greet();
hi();
}
public static void main(String... args) {
Test myApp = new Test();
myApp.sayHello();
}
}
How can I avoid that error with #CompileStatic annotation?
You can write it as a closure. This implies an as HelloWorld and as the interface only has one method groovy can deduct this.
HelloWorld spanishGreeting = {
hi()
System.out.println("spanishGreeting");
}
above code is groovy 2.3; with earlier groovy 2 versions it needs an explicit cast like
def spanishGreeting = {/*...*/} as HelloWorld
Im trying to write simple things with Apache Wicket (6.15.0) and Groovy (2.2.2 or 2.3.1). And Im having trouble with inner classes.
class CreatePaymentPanel extends Panel {
public CreatePaymentPanel(String id) {
super(id)
add(new PaymentSelectFragment('currentPanel').setOutputMarkupId(true))
}
public class PaymentSelectFragment extends Fragment {
public PaymentSelectFragment(String id) {
super(id, 'selectFragment', CreatePaymentPanel.this) // problem here
add(new AjaxLink('cardButton') {
#Override
void onClick(AjaxRequestTarget target) {
... CreatePaymentPanel.this // not accessible here
}
})
add(new AjaxLink('terminalButton') {
#Override
void onClick(AjaxRequestTarget target) {
... CreatePaymentPanel.this // not accessible here
}
});
}
} // end of PaymentSelectFragment class
} // end of CreatePaymentPanel class
Groovy tries to find a property "this" in CreatePaymentPanel class.. How to workaround this? It is a valid java code, but not groovy.
However,
Test.groovy:
class Test {
static void main(String[] args) {
def a = new A()
}
static class A {
A() {
def c = new C()
}
public void sayA() { println 'saying A' }
class B {
public B(A instance) {
A.this.sayA()
instance.sayA()
}
}
/**
* The problem occurs here
*/
class C extends B {
public C() {
super(A.this) // groovy tries to find property "this" in A class
sayA()
}
}
}
}
Above code wont work, the same error occurs, like in Wicket's case.
And TestJava.java, the same and working:
public class TestJava {
public static void main(String[] args) {
A a = new A();
}
static class A {
A() {
C c = new C();
}
public void sayA() {
System.out.println("saying A");
}
class B {
public B(A instance) {
instance.sayA();
}
}
/**
* This works fine
*/
class C extends B {
public C() {
super(A.this);
sayA();
}
}
}
}
What I am missing?
You can't refer to a CreatePaymentPanel.this inside of PaymentSelectFragment because there is no instance of CreatePamentPanel that would be accessible there. What would you expect that to evaluate to if it were allowed?
I've been searching why this generic contruction doesn't compile
I get:
Cannot implicitly convert type 'WpfApplication1.CowDao' to 'WpfApplication1.Dao'
public abstract class Animal { }
public class Dog : Animal { }
public class Cow : Animal { }
public abstract class Dao<T> where T : Animal
{
public void Insert(T t);
}
public class DogDao : Dao<Dog> { }
public class CowDao : Dao<Cow> { }
public class Main
{
public Main()
{
Dao<Animal> dao = null;
if (true) dao = new DogDao();
else dao = new CowDao();
}
}
I just want to get to my goal --> making a 'neutral' instance
I think that my construction has to change, but i don't know how
I'm using .NET Framework 4
Thanks
Generics from a derived does not inherit from Generic from a base class so you may not cast one to another. Instead, write an extension method ToGenericParent that converts like that:
public static Generic<Parent> ToGenericParent(this Generic<Derived> derived)
{
return new Generic<Parent>() { Value = derived.Value };
}
Change your Inheritance for your Dao layers as
public class DogDao : Dao<Animal> { }
public class CowDao : Dao<Animal> { }
Edit:
public abstract class Dao<T> where T : Animal
{
public virtual void Insert(T t)
{
}
protected void ExecuteQuery(string quer)
{
}
}
public class DogDao : Dao<Dog>
{
public override void Insert(Dog t)
{
string insert = "INSERT INTO DOG ...";
base.ExecuteQuery(insert);
}
}
public class CowDao : Dao<Cow>
{
public override void Insert(Cow t)
{
string insert = "INSERT INTO COW ...";
base.ExecuteQuery(insert);
}
}
How can I make a type which is a MarkupBuilder but has default constructor which is initialized with a StringWriter and overrides toString() to call the toString() on the StringWriter?
The idea is like the following, but of course initializing instance variables before super constructor calls is not allowed:
class StringWriterMarkupBuilder extends MarkupBuilder {
final def sw = new StringWriter()
StringWriterMarkupBuilder() {
super(sw)
}
#Override String toString() {
sw.toString()
}
}
Sorry, I finally figured out a solution by digging into the Groovy source code for MarkupBuilder!:
class StringWriterMarkupBuilder extends MarkupBuilder {
StringWriterMarkupBuilder() {
//MarkupBuilder.this(new IndentPrinter(new PrintWriter(writer)))
super(new StringWriter())
}
#Override String toString() {
//IndentPrinter.PrintWriter.StringWriter
return super.getPrinter().out.out.toString()
}
}
You could also do this with the metaClass like so:
import groovy.xml.MarkupBuilder
MarkupBuilder createSWMB() {
new StringWriter().with { sw ->
new MarkupBuilder( sw ).with { mb ->
mb.metaClass.toString = { -> sw.toString() }
mb
}
}
}
MarkupBuilder mb = createSWMB()
mb.root {
names {
name( first:'tim', second:'yates' )
}
}
println mb.toString()