Questions tagged [unmodifiable]
67 questions
50
votes
9 answers
Collections.unmodifiableList and defensive copy
If I write
List a1 = Arrays.asList(1, 2, 3);
List a2 = Collections.unmodifiableList(a1);
a2 is read-only but if I write
a1.set(0,10);
then a2 is also modified.
If in the API is said:
Returns an unmodifiable view of the specified…
xdevel2000
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41
votes
5 answers
What does Collections.unmodifiableSet() do in Java?
I can see that Collections.unmodifiableSet returns an unmodifiable view of the given set but I don't understand why we can't just use the final modifier to accomplish this.
In my understanding, final declares a constant: something that cannot be…
Roman
- 124,451
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39
votes
3 answers
When is the unmodifiablemap (really) necessary?
I have a map of constants, like this:
private static Map _typesMap =
new HashMap() {
{
put ("string", 'S');
put ("normalizedString", 'N');
put ("token", 'T');
…
Paulo Guedes
- 7,189
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24
votes
3 answers
Is there any performance risk to Collections.unmodifiableList?
I suggested returning Collections.unmodifiableList() instead of directly returning a member variable, and my colleague is concerned that there would be a performance hit. Of course the best answer is to measure it, and we may do that - but I'd like…
Carl Manaster
- 39,912
- 17
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24
votes
7 answers
Java collections API: why are Unmodifiable[List|Set|Map] not publicly visible classes?
Collections.unmodifiableList(...) returns a new instance of a static inner class UnmodifiableList. Other unmodifiable collections classes are constructed same way.
Were these classes public, one had two advantages:
ability to indicate a more…
java.is.for.desktop
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19
votes
9 answers
Does the unmodifiable wrapper for java collections make them thread safe?
I need to make an ArrayList of ArrayLists thread safe. I also cannot have the client making changes to the collection. Will the unmodifiable wrapper make it thread safe or do I need two wrappers on the collection?
WolfmanDragon
- 7,851
- 14
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18
votes
3 answers
Returning an unmodifiable map
Using Collections.unmodifiableMap(...), I'm trying to return an unmodifiable view of a map. Let's say I have the following method,
public final Map getMap(){
...
return Collections.unmodifiableMap(map);
}
Why is it legal elsewhere…
mre
- 43,520
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18
votes
7 answers
Java unmodifiable array
final Integer[] arr={1,2,3};
arr[0]=3;
System.out.println(Arrays.toString(arr));
I tried the above code to see whether a final array's variables can be reassigned[ans:it can be].I understand that by a final Integer[] array it means we cannot assign…
Emil
- 13,577
- 18
- 69
- 108
17
votes
7 answers
Unmodifiable List in java
I'm trying to set a List unmodifiable.
In my code, I have a method which returns a list.
This list shouldn't be modified, but I don't want to catch the exception returned by the unmodifiableList.
private List listeReferenceSelectAll =…
user2346325
- 201
- 1
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- 4
15
votes
6 answers
How to create a deep unmodifiable collection?
I often make a collection field unmodifiable before returning it from a getter method:
private List _xs;
....
List getXs(){
return Collections.unmodifiableList(_xs);
}
But I can't think of a convenient way of doing that if the X above is…
Miserable Variable
- 28,432
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13
votes
1 answer
hashCode and equals for Collections.unmodifiableCollection()
The Collections class has a number of static helper methods to provide read-only views of various collection types, such as unmodifiableSet(), unmodifiableList(), etc. For these view objects, the hashCode() and equals() methods forward calls to the…
mergeconflict
- 8,156
- 34
- 63
12
votes
2 answers
ConcurrentModificationException in unmodifiable collection
I have this code below, and I'm getting a ConcurrentModificationException by executing the following line:
filterCardsToDevice(getCollection());
the code:
private List filterCardsToDevice(Collection col) {
final List…
Pedro Estevão
- 982
- 1
- 13
- 41
10
votes
6 answers
How to return a thread safe/immutable Collection in Java?
In the project I am coding, I need to return a thread safe and immutable view from a function. However, I am unsure of this. Since synchronizedList and unmodifiableList just return views of a list, I don't know…
zw324
- 26,764
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8
votes
3 answers
How to reverse an unmodifiable List in java
I am trying to reverse an unmodifiable list. However i have tried to achieve it but Is it possible to update or reverse and unmodifiable list? I know we can do it with Google Immutable List
import java.util.*;
public class ImmutableList
{
public…
vkrams
- 7,267
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8
votes
1 answer
Unmodifiable lists in C#
In Java, one can use the Collections#unmodifiableList() method to create an unmodifiable list from an existing List object. Is there any counterpart in C# ? I'm new to the language and haven't been able to find anything like this in the MSDN docs.
Alex Marshall
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