First of all, I want to share that i'm an experienced Java developer and that this isn't a newbie question.
We all know the test to check if a given index is within the bounds of a List. Namely:
if (index >= 0 && index < list.size())
I was wondering if the introduction of Java 8 created some new method somewhere that could do this test. Something like:
if (list.isWithinBounds(index))
Google gave me no results and I can't find any method in the new APIs. So maybe the community knows if there's something available like this.
I'm not interested in third party libraries which solved this.
Not exactly an answer - just an extra option for helper method placement in java 8. No way to easily attach the helper interface though, so is not a viable solution.
public interface MyList<E> extends List<E> {
default boolean isWithinBounds(int index) {
return 0 <= index && index < this.size();
}
}
static class MyArrayList<E> extends ArrayList<E> implements MyList<E> {
}
public void testList() {
MyList<String> l = new MyArrayList<>();
l.add("1");
l.add("2");
l.add("3");
assert(l.isWithinBounds(2));
assert(!l.isWithinBounds(3));
}
Related
I got this piece of code, I am learning from tutorial. I want to return an element by url which looks like clients/1 instead of clients?id=1. How can I achieve this? Also, can the code below be made easier way?
#GetMapping
public Client getClient(#RequestParam int id) {
Optional<Client> first = clientList.stream().filter(element -> element.getId() == id).findFirst();
return first.get();
}
You may want to use #PathVariable as follows:
#Controller
#RequestMapping("/clients")
public class MyController {
#GetMapping("/{id}")
public Client getClient(#PathVariable int id) {
return clientList.stream().filter(element -> element.getId() == id).findFirst().orElseThrow();
}
Please note, the Optional can be unpacked with orElseThrow method. This will throw a NoSuchElementException in case there is no element found for the id.
Other solution would be to use orElse(new Client(...)) to return a default value if nothing is found.
get() is not really recommended to be used. From the JavaDoc of the get() method:
API Note:
The preferred alternative to this method is orElseThrow().
Even though get() may also throw a NoSuchElementException, similar to orElseThrow, usually the consensus is that get should not be used without isPresent, or should not be used at all. There several other methods to unpack the Optional without forcing you write an if.
The whole idea of the Optional is to overcome this by forcing you to think about the case when there is no value inside.
I've created a very neat way of implementing a PATCH method for my Web.API project by making use of an ExpandoObject as a parameter. As illustrated below:
[HttpPatch, Route("api/employee/{id:int}")]
public IHttpActionResult Update(int id, [FromBody] ExpandoObject employee)
{
var source = Repository.FindEmployeeById(id);
Patch(employee, source);
Repository.SaveEmployee(source);
return Ok(source);
}
However, when generating documentation ApiExplorer is at a loss as to what to do with the ExpandoObject, which is totally understandable. Would anyone have any ideas on how to manipulate the ApiExplorer to provide some sensible documentation?
My idea was to maybe introduce an new attribute which points to the actual Type that is expected:
public IHttpActionResult Update(int id, [FromBody, Mimics(typeof(Employee))] ExpandoObject employee)
{
...
}
But I have no idea where to start, any ideas or suggestions are welcome.
So this has been the source of some late evenings in order to get the Api Explorer to play along with our developed Http Patch mechanism. Truth be told, I'd probably should do a bit of a proper write up to full explain the mechanics behind the whole idea. But for those of you who landed on this page because you want the Api explorer to use a different type in the documentation, this is where you need to look:
Open HelpPageConfigurationExtensions.cs and locate the following method:
//File: Areas/HelpPage/HelpPageConfigurationExtensions.cs
private static void GenerateRequestModelDescription(HelpPageApiModel apiModel, ModelDescriptionGenerator modelGenerator, HelpPageSampleGenerator sampleGenerator)
{
....
}
this is the location where the parameter information is available to you and also provides you with the ability to replace/substitute parameter information with something else. I ended up doing the following to handle my ExpandoObject parameter issue:
if (apiParameter.Source == ApiParameterSource.FromBody)
{
Type parameterType = apiParameter.ParameterDescriptor.ParameterType;
// do something different when dealing with parameters
// of type ExpandObject.
if (parameterType == typeof(ExpandoObject))
{
// if a request-type-attribute is defined, assume the parameter
// is the supposed to mimic the type defined.
var requestTypeAttribute = apiParameter.ParameterDescriptor.GetCustomAttributes<RequestTypeAttribute>().FirstOrDefault();
if (requestTypeAttribute != null)
{
parameterType = requestTypeAttribute.RequestType;
}
}
}
Just, note that the RequestTypeAttribute is something I devised. My WebApi endpoint looks like this now:
public IHttpActionResult Update(int id,
[FromBody, RequestType(typeof(Employee))] ExpandoObject employee)
Thank you to everyone who took time to look into the problem.
This seems to be a problem that comes up a lot. I've been coming up with the same solution nearly every time but was curious if people have a better method of accomplishing this.
I have one class that is a list of instances of another class. The state of the parent class is dependent upon state of ALL the children
As an example. Say I have the following classes
class Box
{
int _objectId= <insert_unique_id>;
int _itemCount = 0;
public void AddItem()
{
_itemCount = Max(_itemCount + 1, 5);
}
public int GetId()
{
return _objectId;
}
public bool IsFull()
{
return _itemCount == 5
}
}
class BiggerBox
{
Map<int, Box> _boxes;
public void AddToBox(int id)
{
_boxes[id].AddItem();
}
public bool IsFull()
{
foreach(var box in _boxes.Values)
if(!box.IsFull())
return false;
return true;
}
}
All additions to a "Box" are done via the BiggerBox.AddToBox call. What I would like to do is be able to determine box.IsFull() without iterating over every single item every time we add an element.
Typically i accomplish this by keeping a SET or a separate collection of what items are full.
Curious, has anyone come up to an ingenious solution to this or is the simple answer that there is no other way?
There are two things you need to do in order to accomplish what you want:
Be able to control every entrypoint to your collection
React to changes to the objects in the collection
For instance, if the objects in the collection are mutable (meaning, they can change after being added to your collection) you need your main object to react to that change.
As you say, you could create a separate set of the objects that are full, but if the objects can change afterwards, when they change you either need to take them out of that set, or add them to it.
This means that in order for you to optimize this, you need some way to observe the changes to the underlying objects, for instance if they implement INotifyPropertyChanged or similar.
If the objects cannot change after being added to your main object, or you don't really care if they do, you just need to control every entrypoint, meaning that you basically need to add the necessary checks to your AddItem method.
For your particular types I would implement an event on the Box class so that when it is full, it fires the event. Your BiggerBox class would then hook into this event in order to observe when an underlying box becomes full.
You can upkeep the number of complete (or non-complete) boxes in BiggerBox class, and update it in all the functions.
E.g., in AddToBox it could be:
bool wasFull = _boxes[id].IsFull;
_boxes[id].AddItem();
if (!wasFull && _boxes[id].IsFull) // After this update box has become full.
completeBoxes += 1;
It is also possible to implement this upkeep procedure in other hypothetical functions (like RemoveFromBox, AddBox, RemoveBox, etc.)
How do I fetch the Measurement System setting value in javascript?
I'm guessing that it would be throw some WinJS call.
The logical place would be Windows.Globalization, but not seeing if offered there. One pretty simple workaround - faster to write than to research the setting :) is to create a Windows Runtime Component in C# that calls in to System.Globalization:
namespace WindowsRuntimeComponent
{
public sealed class RegionalSettings
{
public bool isMetric()
{
return System.Globalization.RegionInfo.CurrentRegion.IsMetric;
}
}
}
Then add as a reference to your JavaScript app and invoke there:
var r = new WindowsRuntimeComponent.RegionalSettings;
var isMetric = r.isMetric();
I see a lot of legacy .Net 1.1-style code at work like in example below, which I would like to shrink with the help of an auto-property. This will help many classes shrink by 30-40%, which I think would be good.
public int MyIntThingy
{
get
{
return _myIntThingy;
}
set
{
_myIntThingy = value;
}
} private int _myIntThingy = -1;
This would become:
public int MyIntThingy
{
get;
set;
}
And the only question is - where do I set MyIntThingy = -1;?
If I wrote the class from the start, then I would have a better idea, but I did not. An obvious answer would be: put it in the constructor. Trouble is: there are many constructors in this class. Watching the initialization to -1 in the debugger, I see it happen (I believe) before the constructor gets called. It is almost as if I need to use a static constructor as described here:
http://www.c-sharpcorner.com/uploadfile/cupadhyay/staticconstructors11092005061428am/staticconstructors.aspx
except that my variables are not static. Java's static initializer comes to mind, but again - my variables are not static. http://www.glenmccl.com/tip_003.htm
I want to make stylistic but not functional changes to this class. As crappy as it is, it has been tested and working for a few years now. breaking the functionality would be bad. So ... I am looking for shorter, sweeter, cuter, and yet EQUIVALENT code. Let me know if you have questions.
I'm afraid that you have no option.
If you want to use an auto-property with an initial value that differs from the type's default value then you'll need to set the initial value in the constructor(s).
If you just need a stylistic, non-breaking change, consider changing the format a little:
public int MyIntThingy
{
get { return _myIntThingy; }
set { _myIntThingy = value; }
}
private int _myIntThingy = -1;
Isn't that prettier?
And consider using auto-properties for future code only. It sounds too risky to use them on existing code, unless there are no default values.