I need a clean copy of a Vector not a reference.
In Swing I use Vector.clone(); (Not Allowed in codenmeone complains its protected.)
In Codenameone I tried Vector someName = new Vector((Vector)anotherVector)
someName becomes a referance as what ever changes are made to anotherVector, someName inherits those changes.
Thoughts?
Best Regards
The new vector approach works but it isn't a deep copy of the elements within. Unfortunately you can't do a deep copy since clone() requires reflection which we don't have. Unfortunately there's no easy answer. You would need to literally go over every element and create a copy of that element since we can't generically duplicate it.
This can be relatively simple, assuming a vector of MyObject which has a constructor that accepts an existing instance then something like this will work:
Vector<MyObject> newVector = new Vector<>();
for(MyObject obj : oldVector) {
newVector.add(new MyObject(obj));
}
Related
I have a query regarding a concept.
Are dynamic arrays in c# also called list? Or they are totally different?
C# does not have a dynamic array type. However, you can use a List as a dynamic array, given that it supports indexed access:
List<string> list = new List<string>();
list.Add("Hello");
list.Add("Goodbye");
Console.WriteLine(list[1]);
Take a look at Generic Lists.
Since it's the first link I found out when looking for this difference I would like to contribute a little.
The Nitin Bisht response is not entirely wrong, but by most of programming definitions a dynamic array is a type of array that can be set when the program is already running, simply put, it's size is set during run time not in compilation.
In C# this is written as:
string[] myDynamicArray;
myDynamicArray = SomeMethodThatReturnsAnCollection().ToArray();
Other way would be a method which returns an existing array like:
string[] myDynamicArray;
myDynamicArray = SomeMethodThatReturnsAnArray();
Those are Dynamic Arrays, you don't tell your program which size it has but inside the logic of that context this will be decided.
Those Arrays in C# has the Resize method, which enables the programmer to grow the array, which I believe it was the Nitin Bisht and so many others interpretation around that question, but this is a wrong assumption, resizable is different than dynamic.
Instead of using Resize in your Array, you could just use a List type, List in C# implements an Array in it's core, which can be seen here, but it also has the ability to grow in an easier approach than the Array implementation enables us with the Add(T item) List method.
List in C# would be a native Dynamic Resizable Array, some languages call similarly implementations of this structure as Vector, which are not a LinkedList with nodes and pointers for example.
Summarizing the difference in code:
var myList = new List<string> { "initial value" };
myList.Add("New value"); // After add, myList has this new value
var myArray = new string[] { "initial value" };
myArray.Append("New value") // after Append myArray doesnt have a new value
With Append() method what happens is another IEnumerable collection is created with the new value, so if you iterate through both collections you will see that the list prints out the new value but the array doesn't, in that case one way you can fix that is doing this:
string[] myArray;
myArray = myArray.Append("New value").ToArray(); // now it will work
The difference here is that myArray variable is being rewritten with the new array generated by .Append().ToArray() line, in the List example the Add() method will resize and then add the new value.
Important to note that this resize is done in a similar manner than what we did with the Append() "fixed" code, the List creates a new Array with increased size and copies it's original contents to this new Array.
You can use the resources given by the Array class to get to the same result as the Add() method implemented by List, but off course if you need that method you should just use an List instead of writing your own implementation, very rarely you would have to do it and to be honest your implementation would be probably less efficient than the already built ones.
In summary that is the difference between them, as you can see they have similarities but I would still treat them very differently.
Usually you wanna use an array when you do not expect to grow any further, if that is your case then an array is more useful since it's has less implementations and that brings a performance gain which can be good in a lot of scenarios.
If not, just use lists.
I am writing a VB.NET Class, and I have run into the issue of needing to create an array of actions. How does one do that in VB.NET?
UPDATE: I am trying to write a collision detection class that stores objects to collide with, and functions to execute when the collision happens with indexes that line up the object to the function.
So like:
Class CDE
Private Collidables As Windows.Forms.Control()
Private Actions As 'Action Array
There's not enough info to provide a specific answer here, but you would create this array the same as you would create any other array in VB.NET.
Dim actionsArr = New MyAction() {action1, action2, action3, action4}
On a side note, I've always been more fond of using Lists over arrays. It's much easier to add and modify items in a list.
https://msdn.microsoft.com/en-us/library/bb385204.aspx
I am an experienced programmer, but new to second life / LSL. I was wanting to be able to algorithmically create structures, buildings, objects, etc. But, I cannot find a function that will actually "create" a new prim with a given set of properties and place it in the environment. Can this be done?
Not easily - what you'd need to do is have a base controller prim, which contains a second prim.
This second prim would have a script in which when rezzed would listen to the base controller, and act on parameters passed to it by transforming it's own properties.
I am playing around with OOP in MATLAB, and I have the following constructor:
function obj = Squadron(num_fighters, num_targets, time_steps)
if nargin == 0
num_targets = 100;
time_steps = 100;
num_fighters = 10;
end
obj.num_shooters = num_fighters;
for iShooter = 1:obj.num_shooters
a(iShooter) = Shooter(num_targets, time_steps);
end
obj.ShooterArray = a;
obj.current_detections = zeros(num_fighters, num_targets);
end
That temporary variable 'a' smells terrible. Is there a better way to initialize an array of objects, I wish there was a push/pop method. I am sure there is a better way to do this.
Looks like you are trying to create an array of handle objects (Shooters) and store it inside the property of another handle object (a Squardron). I have had a very similar problem discussion that might help you.
In short: What you are doing might not be pretty - but might be pretty good already.
When creating an array in Matlab it is usually a good Idea to do some pre-allocation to reserve memory which speeds up performance significantly.
In a normal case something like this:
a=zeros(1,1000);
for n=1:1000
a(n)=n;
end
(here a=1:1000; would be even better)
For objects the pre-allocation works by assigning one of the objects to the very last field in the array. Matlab then fills the other fields before that with objects (handles) that it creates by calling the constructor of that object with no arguments (see Matlab help). Hence a pre-allocation for objects could look like this:
a(1,1000)=ObjectConstructor();
for n=1:1000
a(n)=ObjectConstructor();
end
or simply
for n=1000:-1:1
a(n)=ObjectConstructor();
end
Making sure Shooter can be called with no arguments you should be able to do something like:
for iShooter = obj.num_shooters:-1:1
obj.ShooterArray(iShooter) = Shooter(num_targets, time_steps);
end
However, it turns out that for some reason this direct storing of an array of objects in another object's property creates very bad performance. (Probably the array pre-allocation does not work well in this case). Hence using an auxiliary variable and allocating the full array at once to the property is in this case is a good idea to increase performance.
I would try:
for iShooter = obj.num_shooters:-1:1
a(iShooter) = Shooter(num_targets, time_steps);
end
obj.ShooterArray = a;
Again - for more detail see this discussion
There are a couple of ways to handle this situation...
Building object arrays in the constructor:
You could modify your Shooter class such that when you pass arrays of values it creates an array of objects. Then you could initialize ShooterArray like so:
obj.ShooterArray = Shooter(repmat(num_targets,1,num_fighters),...
repmat(time_steps,1,num_fighters));
Replicating instances of a value class:
If Shooter is a value class, and each object is going to be exactly the same (i.e. you don't initialize any of its default properties to random values), then you can create just one object and replicate it using REPMAT:
obj.ShooterArray = repmat(Shooter(num_targets,time_steps),1,num_fighters);
Unfortunately, if Shooter is a subclass of the handle class, you can't just replicate it as you can with a value class. You would actually be replicating references to just one object, when you really need a number of separate objects each with their own unique reference. In such a case, your current code is likely the best solution.
I have created an array in the implementation of my class loginController. Now I want to use this array (with its objects) in another class of my project. What is the right way to import it?
You really need to specify the language.
In general, if the array is a member variable in one class, it's considered bad form to directly use it from another class. This violates the "encapsulation" idea that is quite the thing in object-oriented programming.
The preferred thing to do is often to add methods, called "getters" and "setters", to the class owning the array, or make it available by some other more structural means, which depend on the exact semantics and usage of the array. It might, for instance, not be required that outside users even know that it is an array.
There is no right way given this information. What is located in the array, only integers or strings/objects etc. Do you store objects of pointers to objects?
Passing the array is the sameway as passing any other object to a function
The general answer would be: declare it as public
It is not very good thing to do but as a beginner, you can start with that.