Create an Object from an Array Class

[Z]

I am using reflection to getmethod(methodName, Class parameters) and
invoke(object, obj[] parameters) methods from some Objects.

My problem is:

Say: I want to invoke a method that takes String[] object as parameter
(I was able to getmethod correctly). When I try to create an object
(to pass as args to invoke):

Object someObject= (Object) String[].class.newInstance();

(Note that the object is not always an instance of String[]... it
could be an instance of SomeOtherClass[])

I do get the following exception:

java.lang.InstantiationException: [Ljava.lang.String;

My question is:

Does the "[L" at the beginning and the ";" at the end have a meaning?
How can I solve this problem?

I am using IntelliJ 6.0.5.

Thanks in advance.

 

[Joshua Cranmer]

I am using reflection to getmethod(methodName, Class parameters) and
invoke(object, obj[] parameters) methods from some Objects.

My problem is:

Say: I want to invoke a method that takes String[] object as parameter
(I was able to getmethod correctly). When I try to create an object
(to pass as args to invoke):

Object someObject= (Object) String[].class.newInstance();

(Note that the object is not always an instance of String[]... it
could be an instance of SomeOtherClass[])

RTFM:
[ From Class.newInstance(): ]
Throws:
[ ... ]
InstantiationException - if this Class represents an abstract
class, an interface, an array class, a primitive type, or void; or if
the class has no nullary constructor; or if the instantiation fails for
some other reason.
[ ... ]

Arrays cannot be created with a new instance, because they are a
special-case class.

My question is:

Does the "[L" at the beginning and the ";" at the end have a meaning?

Yes, this is the internal representation of the class (it means that
this is an array of java.lang.String's).

How can I solve this problem?

What you are probable intending is something like this:

Method m = Class.forName("some.pkg.Type").getMethod("main",
String[].class);
m.invoke(null, new String[0]);

I am using IntelliJ 6.0.5.

Java version matters, not IDE version.

 

[Joshua Cranmer]

What you are probable intending is something like this:

Method m = Class.forName("some.pkg.Type").getMethod("main",
String[].class);
m.invoke(null, new String[0]);

If the type of array must be determined at runtime, the following idiom
can also be used:

// arrayType is a class representing the type we want.
Object array = Array.newInstance(arrayType, 0); // Empty array

Array has another overloaded version that handles multiple array dimensions.

 

[Z]

Thanks for the clarifications. I hope that my phrasing of the question
shows where I am stuck.

What I am intending to do is:

//here is how my program is flowing

String className = namesOfAllClasses[j]; //I have it coming through a
loop

Class class1 = Class.forName(className);

Fields fields = class1.getDeclaredFields(); //assuming that all fields
are Class type (not primitive)

for (int i=0; i < fields.length; i++) {
Class newClass = Class.forName(fields.getType().getName()); //
create a class of the field type
Object newObject = newClass.newInstance(); //create an object of
the new field type
Method m = newClass.getMethod(methodName, newClass); /*get method;
we can assume it's "set"+fields.getName()*/
Object arguments[] = {"dummy"};
m.invoke(newObject, arguments);
}

/*
When a field is someClass[], I am facing troubles since now the
fields.getType().getName() = L[some.pkg.name.someClass;
In this case:
Class newClass = Class.forName(fields.getType().getName()) is
returning with a result (no exceptions)

But using the newInstance is generating exceptions since it's a
special-case class as you explained.

You have used
m.invoke(null, new String[0]); //it gave me back a
nullPointerRxception even though it's a static method

My problem is that the second parameter in invoke does not have to be
a String type for the parameter object but is an object instance of
the L[some.pkg.name.someClass; (object array)

Example: This method looks like this in ClassName.java

public void setsomeObjectProperty(some.pkg.name.someClass[]
someObjectProperty) {
this.someObjectProperty= someObjectProperty;
}

Any tips?
*/

Thanks again for your time

I am using reflection to getmethod(methodName, Class parameters) and
invoke(object, obj[] parameters) methods from some Objects.

My problem is:

Say: I want to invoke a method that takes String[] object as parameter
(I was able to getmethod correctly). When I try to create an object
(to pass as args to invoke):

Object someObject= (Object) String[].class.newInstance();

(Note that the object is not always an instance of String[]... it
could be an instance of SomeOtherClass[])

RTFM:
[ From Class.newInstance(): ]
Throws:
[ ... ]
InstantiationException - if this Class represents an abstract
class, an interface, an array class, a primitive type, or void; or if
the class has no nullary constructor; or if the instantiation fails for
some other reason.
[ ... ]

Arrays cannot be created with a new instance, because they are a
special-case class.

My question is:

Does the "[L" at the beginning and the ";" at the end have a meaning?

Yes, this is the internal representation of the class (it means that
this is an array of java.lang.String's).

How can I solve this problem?

What you are probable intending is something like this:

Method m = Class.forName("some.pkg.Type").getMethod("main",
String[].class);
m.invoke(null, new String[0]);

I am using IntelliJ 6.0.5.

Java version matters, not IDE version.

 

[Lasse Reichstein Nielsen]

I am using reflection to getmethod(methodName, Class parameters) and
invoke(object, obj[] parameters) methods from some Objects.

My problem is:

Say: I want to invoke a method that takes String[] object as parameter
(I was able to getmethod correctly). When I try to create an object
(to pass as args to invoke):

Object someObject= (Object) String[].class.newInstance();

That fails, because the array class does not have a normal
constructor. Here you try to invoke a default constructor.

(Note that the object is not always an instance of String[]... it
could be an instance of SomeOtherClass[])

I do get the following exception:

java.lang.InstantiationException: [Ljava.lang.String;

My question is:

Does the "[L" at the beginning and the ";" at the end have a meaning?

Yes. Java writes the name of and array of object type as "[L" followed
by the name of the class and ended by ";". I.e., the type
my.foo.Foo[]
has the name "[Lmy.foo.Foo;". Arrays of base types have other abbreviations,
e.g., "[I" for int[].

How can I solve this problem?

Array.newInstance(String.class, 0); // equivalent to: new String[0]

/L

 

[Daniel Pitts]

I am using reflection to getmethod(methodName, Class parameters) and
invoke(object, obj[] parameters) methods from some Objects.
My problem is:
Say: I want to invoke a method that takes String[] object as parameter
(I was able to getmethod correctly). When I try to create an object
(to pass as args to invoke):
Object someObject= (Object) String[].class.newInstance();
(Note that the object is not always an instance of String[]... it
could be an instance of SomeOtherClass[])

RTFM:
[ From Class.newInstance(): ]
Throws:
[ ... ]
InstantiationException - if this Class represents an abstract
class, an interface, an array class, a primitive type, or void; or if
the class has no nullary constructor; or if the instantiation fails for
some other reason.
[ ... ]

Arrays cannot be created with a new instance, because they are a
special-case class.

My question is:
Does the "[L" at the beginning and the ";" at the end have a meaning?

Yes, this is the internal representation of the class (it means that
this is an array of java.lang.String's).

How can I solve this problem?

What you are probable intending is something like this:

Method m = Class.forName("some.pkg.Type").getMethod("main",
String[].class);
m.invoke(null, new String[0]);

I am using IntelliJ 6.0.5.

Java version matters, not IDE version.

Thanks for the clarifications. I hope that my phrasing of the question
shows where I am stuck.

What I am intending to do is:

//here is how my program is flowing

String className = namesOfAllClasses[j]; //I have it coming through a
loop

Class class1 = Class.forName(className);

Fields fields = class1.getDeclaredFields(); //assuming that all fields
are Class type (not primitive)

for (int i=0; i < fields.length; i++) {
Class newClass = Class.forName(fields.getType().getName()); //
create a class of the field type
Object newObject = newClass.newInstance(); //create an object of
the new field type
Method m = newClass.getMethod(methodName, newClass); /*get method;
we can assume it's "set"+fields.getName()*/
Object arguments[] = {"dummy"};
m.invoke(newObject, arguments);
}

/*
When a field is someClass[], I am facing troubles since now the
fields.getType().getName() = L[some.pkg.name.someClass;
In this case:
Class newClass = Class.forName(fields.getType().getName()) is
returning with a result (no exceptions)

But using the newInstance is generating exceptions since it's a
special-case class as you explained.

You have used
m.invoke(null, new String[0]); //it gave me back a
nullPointerRxception even though it's a static method

My problem is that the second parameter in invoke does not have to be
a String type for the parameter object but is an object instance of
the L[some.pkg.name.someClass; (object array)

Example: This method looks like this in ClassName.java

public void setsomeObjectProperty(some.pkg.name.someClass[]
someObjectProperty) {
this.someObjectProperty= someObjectProperty;
}

Any tips?
*/

Thanks again for your time

First, please don't top-post. Reply after the bottom or interleaved.

Second, Don't look for set+name or get+name methods. Use the
introspection API. (java.beans.*). There is more to JavaBeans than just
a naming convention.

Also, ask yourself if you REALLY need to use reflection/introspection at
all. I wrote an article about it on my blog sometime last year
<http://virtualinfinity.net/wordpress/>

I'll post the exact link when I have a chance to look it up.