I have a setResultValue method which accepts Object as argument
public class CommandResult {
// other methods
public void setResultValue(Object resultValue) {
this.resultValue = resultValue;
}
And am trying to pass a java.io.File instance file to this method as below
new CommandResult.setResultFile(file);
And am seeing the below error
groovy.lang.MissingMethodException: No signature of method: com.dc.core.behavior.command.model.impl.CommandResult.setResultFile() is applicable for argument types: (java.io.File) values:
Possible solutions: setResultValue(java.lang.Object), getResultValue()
Isnt the method setResultFile supposed to accept file since Object is the super class of all instances?
Your method signature is setResultValue. You call setResultFile.
Related
A closure with a delegate that is not a groovy-object (e.g. coming from a normal java-library), will never call the 'methodMissing' object added to that delegate using it's metaclass, if the call is made 'implicit' (i.e. not calling it explicitly on 'delegate' within the closure.)
The code below does an explicit and an implicit call to a non-existing method; it does so on a Groovy-class instance, a GString and a non-groovy object. The only one that fails is the implicit call to a non-groovy-object (i.c. ArrayList).
(You can see and run the same code online:
https://groovyconsole.appspot.com/edit/5200829376102400)
Not sure if this is a bug or a limitation - references to methodMissing defined through metaClass are pretty scarce. Any insightful comments would be welcome.
class ClosureDelegate {
def testMissingMethod(def someObject) {
someObject.metaClass.methodMissing = { String name, args ->
println name
}
def closure = {
delegate.anything()
anything() // this one fails on non-groovyclasses
}
closure.delegate = someObject
closure.resolveStrategy = Closure.DELEGATE_ONLY
closure()
}
}
class TestObject {}
println "testing with TestObject"
new ClosureDelegate().testMissingMethod(new TestObject())
println "testing with GString"
new ClosureDelegate().testMissingMethod("${new Date()}")
println "testing with ArrayList"
new ClosureDelegate().testMissingMethod(new ArrayList())
testing with TestObject
anything
anything
testing with GString
anything
anything
testing with ArrayList
anything
Caught: groovy.lang.MissingMethodException: No signature of method: ClosureDelegate$_testMissingMethod_closure2.anything() is applicable for argument types: () values: []
Possible solutions: toString(), toString(), any(), any()
According to the ClosureMetaClass implementation, this behavior is expected. Take a look at the following part that starts at line 275 in that file:
switch (resolveStrategy) {
case Closure.TO_SELF:
break;
case Closure.DELEGATE_ONLY:
method = getDelegateMethod(closure, delegate, methodName, argClasses);
callObject = delegate;
if (method == null) {
invokeOnDelegate = delegate != closure && (delegate instanceof GroovyObject);
}
break;
Source: src/main/java/org/codehaus/groovy/runtime/metaclass/ClosureMetaClass.java#L275-L284
The invokeOnDelegate boolean flag verifies if the delegate object extends GroovyObject (the default parent class for all Groovy classes.) When you execute your code with Groovy classes, this flag is set to true and the anything method from the delegate object gets invoked. In the case of non-Groovy classes, MethodMissingException is thrown.
You can debug this behavior by setting the breakpoint in AbstractCallSite.callCurrent(GroovyObject receiver) line 160. You will see that in all cases the method anything is not found in the closure, but in the first two cases invokeOnDelegate is evaluated to true, and the invokeMethod on delegate object is executed. It does not happen in the third case, because ArrayList is not an instance of GroovyObject.
I am experimenting with some dynamic variable creation with GroovyShell and encountered an issue. First, the working code:
static def defVar(def glob) {
glob.setVariable('test', new Test())
}
class MyBinding extends Binding {
}
class Test {
def call() {
println("--- hello ---")
}
}
Binding glob = new MyBinding()
GroovyShell shell = new GroovyShell(glob)
defVar(glob)
shell.parse('test()').run()
This gives me the expected output:
--- hello ---
However, I want to call setVariable() dynamically when getVariable() is called, something like this:
static def defVar(def glob) {
glob.setVariable('test', new Test())
}
class MyBinding extends Binding {
def getVariable(String name) {
if (! hasVariable('test')) {
BindingTest.defVar(this)
}
return super.getVariable(name)
}
}
class Test {
def call() {
println("--- hello ---")
}
}
Binding glob = new MyBinding()
GroovyShell shell = new GroovyShell(glob)
//defVar(glob)
shell.parse('test()').run()
But this fails with the below error:
Caught: groovy.lang.MissingMethodException: No signature of method: Script1.test() is applicable for argument types: () values: []
Possible solutions: getAt(java.lang.String), use([Ljava.lang.Object;), use(java.lang.Class, groovy.lang.Closure), use(java.util.List, groovy.lang.Closure), wait(), wait(long)
groovy.lang.MissingMethodException: No signature of method: Script1.test() is applicable for argument types: () values: []
Possible solutions: getAt(java.lang.String), use([Ljava.lang.Object;), use(java.lang.Class, groovy.lang.Closure), use(java.util.List, groovy.lang.Closure), wait(), wait(long)
at Script1.run(Script1.groovy:1)
at Script1$run.call(Unknown Source)
at BindingTest.run(BindingTest.groovy:23)
When I added tracing code like this:
class MyBinding extends Binding {
def getVariable(String name) {
if (! hasVariable(name)) {
BindingTest.defVar(this)
}
println("getVariable: ${name}: ${super.getVariable(name).getClass().getName()}")
return super.getVariable(name)
}
void setVariable (String name, def val) {
println("setVariable: ${name}: ${val.getClass().getName()}")
super.setVariable(name, val)
}
def getProperty(String name) {
println("getProperty: ${name}: ${super.getProperty(name)}")
return super.getProperty(name)
}
void setProperty (String name, def val) {
println("setProperty: ${name}: ${val.getClass().getName()}")
super.setProperty(name, val)
}
}
In the working case, I get the below output:
setVariable: test: Test
--- hello ---
In the non-working case, I get this output:
setVariable: test: Test
getVariable: test: Test
Caught: groovy.lang.MissingMethodException: No signature of method: Script1.test() is applicable for argument types: () values: []
...
Two questions:
In the working scenario, why is there no getVariable?
In the non-working scenario, why is the Test object returned by getVariable getting rejected?
Note that this issue is specific to callable values. If I set a simple value such as a string, to test, then both approaches work fine. E.g., with this sort of a change:
...
static def defVar(def glob) {
glob.setVariable('test', '--- hello ---')
}
...
shell.parse('println(test)').run()
I get the below identical output with both approaches:
setVariable: test: java.lang.String
getVariable: test: java.lang.String
setVariable: test: java.lang.String
--- hello ---
Though, I am not sure why setVariable gets called twice. I couldn't find any documentation explaining these puzzling behaviors. Could anybody here shed some light on them?
Please note, all the code snippets have been simplified for the ease of demonstrating the problem rather than for their intended purpose
When you use a property as a callable fallback, the Binding.getVariable() method does not get involved. This behavior is controlled by the metaclass, and in your case, it all drives to the execution of the MetaClassImpl.invokePropertyOrMissing() method. This method determines if
test()
should invoke test.call() (in case of an existing property), or should it fallback to the missingMethod() method. Here is what this method implementation looks like:
private Object invokePropertyOrMissing(Object object, String methodName, Object[] originalArguments, boolean fromInsideClass, boolean isCallToSuper) {
// if no method was found, try to find a closure defined as a field of the class and run it
Object value = null;
final MetaProperty metaProperty = this.getMetaProperty(methodName, false);
if (metaProperty != null)
value = metaProperty.getProperty(object);
else {
if (object instanceof Map)
value = ((Map)object).get(methodName);
}
if (value instanceof Closure) { // This test ensures that value != this If you ever change this ensure that value != this
Closure closure = (Closure) value;
MetaClass delegateMetaClass = closure.getMetaClass();
return delegateMetaClass.invokeMethod(closure.getClass(), closure, CLOSURE_DO_CALL_METHOD, originalArguments, false, fromInsideClass);
}
if (object instanceof Script) {
Object bindingVar = ((Script) object).getBinding().getVariables().get(methodName);
if (bindingVar != null) {
MetaClass bindingVarMC = ((MetaClassRegistryImpl) registry).getMetaClass(bindingVar);
return bindingVarMC.invokeMethod(bindingVar, CLOSURE_CALL_METHOD, originalArguments);
}
}
return invokeMissingMethod(object, methodName, originalArguments, null, isCallToSuper);
}
Source: https://github.com/apache/groovy/blob/GROOVY_2_5_X/src/main/groovy/groovy/lang/MetaClassImpl.java#L1262-L1287
Now, pay attention to the branch if (object instanceof Script) and how the binding variable gets retrieved. It tries to retrieve test variable from binding object using:
Object bindingVar = ((Script) object).getBinding().getVariables().get(methodName);
Your code would work if it was:
Object bindingVar = ((Script) object).getBinding().getVariable(methodName);
instead. But it's not.
You can make your second case working if you override getVariables() method instead of getVariable(String name), for instance:
class MyBinding extends Binding {
#Override
Map getVariables() {
return super.getVariables() + [
test: new Test()
]
}
}
Of course, your final implementation might be much more sophisticated. (E.g. you could get super.getVariables() map first, check which variables are missing and add a default variable only if the initial map was missing given variable.) But this is up to you.
Alternatively, consider using methodMissing instead of the binding variable fallback. It could make your code much easier to read and reason about.
I injected overridden method toString into Object.metaClass：
Object.metaClass.toString ={
System.out.println("the string is $delegate")
}
and I thought that following code will execute this method:
1500.toString()
But it didn't not,nothing was printed to the console. That is what exactly confuses me: if something goes bad, then an error is to throw out; if Object.metaClass.toString is found and invoked, then the message will turn up, but why it is not working? What happened inside?
This behavior is correct, because java.lang.Integer overrides Object.toString() with its own implementation. If your assumption was correct then it would mean that you can break overridden method by forcing to use an implementation from parent class.
Consider following Groovy script:
Object.metaClass.toString = {
System.out.println("the string is $delegate")
}
class GroovyClassWithNoToString {}
class GroovyClassWithToString {
#Override
String toString() {
return "aaaa"
}
}
new GroovyClassWithNoToString().toString()
new GroovyClassWithToString().toString()
1500.toString()
Runtime.runtime.toString()
When you run it you will see something like:
the string is GroovyClassWithNoToString#3a93b025
the string is java.lang.Runtime#128d2484
You can see that GroovyClassWithNoToString.toString() called Object.toString() method and its modified version, also Runtime.toString() calls Object.toString() - I picked this class as an example of pure Java class that does not override toString() method.
As you can see overriding toString() method from Object level makes sense for classes that base on Object.toString() implementation. Classes that provide their own implementation of toString() wont use your dynamically modified method. It also explains why following code works:
Object.metaClass.printMessage = {
System.out.println("Hello!")
}
1500.printMessage()
In this example we are adding a new method called printMessage() to Object class and all classes that don't override this method will use this dynamic method we just created. Integer class does not have method like that one so it's gonna print out:
Hello!
as expected.
Also keep in mind that toString() should return a String and it's better to not print anything to output inside this method - you can end up with nasty StackOverflowError caused by circular calls to toString() method.
UPDATE: How toString() method is being picked by Groovy runtime?
Let me show you under the hood what happens when we call following script:
Object.metaClass.toString = {
System.out.println("Hello!")
}
1500.toString()
and let's see what does Groovy during the runtime. Groovy uses Meta Object Protocol (MOP) to e.g. invoke any method called in a Groovy code. In short, when you call any Java or Groovy method it uses MOP as an intermediate layer to find an execution plan for a method - call it directly or use e.g. a method that was injected dynamically.
In our case we use plain Java class - Integer. In this case Groovy will create an instance of PojoMetaMethodSite class to meta class implementation for Java class - an Integer. Every meta method is executed using one of the Groovy groovy.lang.MetaClass implementation. In this case groovy.lang.MetaClassImpl is being used. One of the last methods that picks a method to execute is MetaClassImpl.getMethodWithCachingInternal(Class sender, CallSite site, Class [] params). If you put a breakpoint in the beginning of this method and run a script with a debugger, you will see that this method is executed with following parameters:
In line 1331 you can see that helper method called chooseMethod(e.name, methods, params) is being used:
cacheEntry = new MetaMethodIndex.CacheEntry (params, (MetaMethod) chooseMethod(e.name, methods, params));
This method is responsible for picking the right method to execute when we try to invoke toString() on Integer object. Let's get there and see what happens. Here is what this method implementation looks like:
/**
* Chooses the correct method to use from a list of methods which match by
* name.
*
* #param methodOrList the possible methods to choose from
* #param arguments
*/
protected Object chooseMethod(String methodName, Object methodOrList, Class[] arguments) {
Object method = chooseMethodInternal(methodName, methodOrList, arguments);
if (method instanceof GeneratedMetaMethod.Proxy)
return ((GeneratedMetaMethod.Proxy)method).proxy ();
return method;
}
Source: https://github.com/apache/groovy/blob/GROOVY_2_4_X/src/main/groovy/lang/MetaClassImpl.java#L3158
Now let's see what parameters are received when we call our script:
What is most interesting in our case is the first element of methodOrList.data. It's a method object of:
public java.lang.String java.lang.Integer.toString()
which is the method toString() that Integer class overrides from its parent class. Groovy runtime picks this method, because it is the most accurate from the runtimes point of view - it is the most specific method for Integer class provided. If there is no toString() method overridden at the class level (e.g. Runtime class example I mentioned earlier) then the best candidate for invoking toString() method is a ClosureMetaMethod provided by us in Object.metaClass.toString = .... I hope it gives you a better understanding of what happens under the hood.
I don't think you can override the Object.toString() that way.
But this works:
Integer.metaClass.toString = { ->
System.out.println("the string is $delegate")
}
https://groovyconsole.appspot.com/script/5077208682987520
// What is the technical reason behind this scenarios..?
You're trying to use a statement other than a declaration directly inside the class - rather than within a method. When did you expect the method to get called?
Basically all you can have directly within a type is a bunch of declarations - methods, variables, constructors, events, nested types etc. Method calls (or any other statements) which aren't part of a declaration have to be written within methods, constructors etc.
Method call statement can not be part of a class declaration, but only within Function members declarations scope, such as Methods, Properties, Constructors etc.
For example:
public class ExampleClass
{
private void SayHelloWorld()
{
Console.Writeline("Hello World!");
}
public void CallSayHelloWorldMethod()
{
this.SayHelloWorld();
}
}
At the above example you can see that I call the SayHelloWorld method within the CallSayHelloWorldMethod metod.
Update:
The closest thing I can think of in your case is to use the class's constructor where your method call will be executed as soon as you'll instantiate your class:
public class ExampleClass
{
//The class constructor
public ExampleClass()
{
this.SayHelloWorld();
}
private void SayHelloWorld()
{
Console.Writeline("Hello World!");
}
}
And when you instantiating it, it will be immediately called:
//Your method call will be executed here
ExampleClass exampleClass = new ExampleClass();
You have a few problems... This won't even compile as you are trying to call the method obj.m1() in the class definition.
A obj = new A();
obj.m1(); // Why this code wont work??? --> This must be inside a method
When you create an instance of a class it will create a new member variable called obj which is an instance of A --> A obj = newA() above;
You will now be able to call obj's methods as in your second example.
Also, in order to get this to compile you will need to fix the m2 method:
public void m2() { //--> should have a curly brace
obj.m1(); // But This will work.
}
I have a LWUIT class which has a List, the list itself contains a Label as an item.
My idea simply to make an action for the list when I focus on the label.
I get the following error, when compiling the class:
anonymous Midlet$2 is not abstract and does not override abstract
method focusLost(com.sun.lwuit.Component) in
com.sun.lwuit.events.FocusListener
String s = ("Focus me");
final com.sun.lwuit.Form f = new com.sun.lwuit.Form();
final com.sun.lwuit.List D = new com.sun.lwuit.List();
final com.sun.lwuit.Label l = new com.sun.lwuit.Label(s);
D.addItem(l);
f.addComponent(D);
D.addFocusListener(new com.sun.lwuit.events.FocusListener () {
public void focusGained(com.sun.lwuit.Label l)
{
}
public void focusLost(com.sun.lwuit.Label l)
{
}
});
All details of what is wrong with your code are in the error message, you just need to carefully read it. Look,
word anonymous and sign $ in Midlet$2 tell you something is wrong in the anonymous class.
In your code snippet, there's only one such class: new com.sun.lwuit.events.FocusListener
does not override abstract method focusLost(com.sun.lwuit.Component) means your anonymous class misses a definition of a method with such a signature (signature is method name and type of parameters)
Look closer in the methods you defined in that anonymous class, is there a method compiler is complaining about?
At the first glance, you may think it's there, there's a method called focusLost - but (!) you need to remember that signature is not only method name, but also parameters type - and (!) if you look closer, you'll find out that parameter type is not that is said to be required in error message.
Your anonymous class has method focusLost(com.sun.lwuit.Label) but error message says there should be method with different signature (different parameter type) - focusLost(com.sun.lwuit.Component).
To fix this compilation error, add to the anonymous class new com.sun.lwuit.events.FocusListener a method with required signature: focusLost(com.sun.lwuit.Component).