Generic « Map « Java Collection Q&A

1. Map of collections    stackoverflow.com

I wanted to make Map of Collections in Java, so I can make something like

public void add(K key, V value) {  
    if (containsKey(key)) {
 ...

2. What are the reasons why Map.get(Object key) is not (fully) generic    stackoverflow.com

What are the reasons behind the decision to not have a fully generic get method in the interface of java.util.Map<K,V>. To clarify the question, the signature of the method is ...

3. Java Generics putting on Map>    stackoverflow.com

Is there a way to make the following implementation in a type safe manner?

public void myMethod( Map<String, ? extends List<String>> map )
{
   map.put("foo", Collections.singletonList("bar");
}

4. Why is code that returns a genericized Map generating a compiler warning when assigned to a generic Map?    stackoverflow.com

I have a method with this signature:

   protected final Map<String, Object> buildOutputMappings(
                  ...

5. Accessing a Java generics stored in a Map    stackoverflow.com

Hello
I'm trying to access a custom Java generic stored in a map as below.
Unfortunately I get a type mis-match error.
Now, I can cast it to the type I want because but ...

6. Generic keying across maps: Map from Map and Map    stackoverflow.com

I have a function which returns a one-sided intersection of values between two input maps:

Map<Key, Value> mergeMaps(Map aKeys<CompositeKey, Key>, 
         Map <CompositeKey, Value> ...

7. How do I return List from a method where I sent to put(Object) into a map (got example)    stackoverflow.com

I have the following code

private Map<KEY, Object> values = new HashMap<KEY, Object>();

public void set(KEY key, Object value) {
 values.put(key, value);
}

private Object getObj(KEY key) {
 return values.get(key) == null ? key.getDefaultValue() : ...

8. Generic Factories and Map Values    stackoverflow.com

I have a class with Maps from Ks to Set<V>s, for several different Vs. I'd like to use a generic factory ala:

protected static <T> Set<T> SetFactory(int size) {
   ...

9. Problem using generic map with wildcard    stackoverflow.com

I have a method that returns a map defined as:

public Map<String, ?> getData();

obj.getData().put("key","value")

10. Map generics in Java    stackoverflow.com

I seem to have a bit of misunderstanding with Java Generics and I hope you can help me. I tried to create a map like so:

Map<Debater, int>

11. Type-safe mapping from Class to Thing    stackoverflow.com

I want to make a map-kind of container that has the following interface:

public <T> Thing<T> get(Class<T> clazz);
public <T> void put(Class<T> clazz, Thing<T> thing);

12. Generic Collections and XStream    stackoverflow.com

Is there a way to map (using xstream) a List<Person> to <friends> and List<Things> to <stuff> for example? Thanks!

13. Java Map : Why get(object) not get(K)?    stackoverflow.com

Possible Duplicate:
Java Generics: Why Does Map.get() Ignore Type?

V put(K key,V value);
V get(Object key);

14. Parse an XML structure as a simple, generic set of maps and lists    stackoverflow.com

Somewhat related to http://stackoverflow.com/questions/1537207/how-to-convert-xml-to-java-util-map-and-vice-versa, only even more generic. I have an XML document, and I'd like to convert it to a very generic set of key/value pairs (in Java, that is). ...

15. Compiler complains when I iterate Non-Generics Map in Java    stackoverflow.com

I meet weired problem when I iterate a Non-Generics Map in Java

Map map=new HashMap();
for (Map.Entry entry:map.entrySet()){

}

16. Why does Java Map take an untyped parameter for the get and remove methods?    stackoverflow.com

I ran into a bug in my code where I was using the wrong key to fetch something from a Java map that I believed was strongly typed using Java generics. ...

17. Why is java.util.Map.get(...) not generic?    stackoverflow.com

Possible Duplicate:
What are the reasons why Map.get(Object key) is not (fully) generic

18. Is there a solution to my problem using generics?    stackoverflow.com

I'm implementing some code using the java.util.concurrency framework. I will be passing a collection of callables to a class which will execute them in parallel. I'm trying to work ...

19. Generic method to Sort a Map on Values    stackoverflow.com

I have a small program that is supposed to sort a map based on its values. Here is what I have so far:

    public static <K, V extends ...

20. What does Map mean in Java?    stackoverflow.com

What does Map<?, ?> mean in Java?
I've looked online but can't seem to find any articles on it. edit : I found this on MP3 Duration Java

21. In Java is it possible to create a Map of classes to instances of their class?    stackoverflow.com

I would like to create a map that uses a class as a key to return an instance of that class. Something like:

<T> Map< Class<T>, T > instanceMap = new HashMap< ...

22. How can the generic Map for the font attributes be specified?    stackoverflow.com

I have this method which jdk1.6 complains (no error just warning) about the generic type parameterizing is not used in the Map and ...:

public static Font getStrikethroughFont(String name, int properties, int ...

23. Why does the key parameter in Map.get() is not generic?    stackoverflow.com

Possible Duplicate:
What are the reasons why Map.get(Object key) is not (fully) generic

V get(Object key) ...

24. Map of maps and generics    stackoverflow.com

I want to create a (recursive) map of maps. That is, the value of type of the Map is another Map of the same type as the outer map. For example:

Map<String, ...

25. Default Map in Generics in jdk 1.5    stackoverflow.com

I want default Map to use all HashMaps. key can be String, integer or any data type Value can be String, Integer ..any data type. How to use Map in jdk1.5.

26. Is there any fully generic version of Map.get(), i.e, "V get(K key)"    stackoverflow.com

Since Map.get() is not fully generic, we often find cases where a developer passed a different type of object (and hence bugs). Frequency of such cases went up when we started ...

27. Java generics problem with Map    stackoverflow.com

I have this which should not compile.

public boolean foo(final Map<String, String> map) {
     map.get(1);   // No error here?
}

28. Java Map that is Multi Value and supports generics?    stackoverflow.com

I noticed that there is a MultiValueMap from commons, however it doesn't support generics. Is there such a map that does?

29. classCastException in Map.Entry    stackoverflow.com

there is something about my code that i dont understand. when i execute the following code className1 and value1 get their value right from the entry, but when for the className2 i ...

30. How to create a generic process that read in a tab delimited file, and return a generic Map from it    stackoverflow.com

Almost every project that I work will have some sort of tab delimited file that I need to read in and return a lookup Map of it. I find myself rewrite ...

31. Use Generic on Map    coderanch.com

I like to implement a map to store a bunch of different objects, with the key of the map to be the Class of the object, and the value to be the object itself. So when I attempt to retrieve the cached object, I will pass in the Class type, and the stored instance will be return. Without using Generic: Map ...

32. generics - map of lists    coderanch.com

Yes, unfortunately EJB 3.0 Persistence did not generify their collections, and the Query.getResultList() returns a List and not a List

33. Generics: Nested Map Declaration    coderanch.com

34. Heterogeneous map and generics    coderanch.com

All, I am trying to write a heterogeneous map where I can get compile time type safety. The goal is to have a map of attributes where a producer can put data in and consumer can retrieve it without casting. I am not using any messaging API. This will be used in pure JAVA app without any fancy frameworks. What do ...

35. Generics : Passing a Map of >    coderanch.com

I need some Generics enlightenment. I want to pass a Map of >, but I can't figure out how. Here is a sample : class SuperClass { public void hello() { System.out.println("Hello"); } } class ChildOne extends SuperClass { } class ChildTwo extends SuperClass { } public class Generic { /** * @param args */ public static void ...

36. generics, Map.entrySet() and casting    coderanch.com

37. generics and maps    coderanch.com

38. Generics Question: Map and Map.Entry    coderanch.com

39. What does exactly mean in Map.Entry? Is it a generic?    forums.oracle.com

40. map with generics    forums.oracle.com

please tell me why does this code compile and work [code] @Override protected void customExecute(Map transientVars) { EaProgramFinding eaProgramFinding=(EaProgramFinding)transientVars.get(WorkflowParameters.FINDING_TO_MOVE); } [code] here I am passing a map of key type String and value type object to this method but inside the method I am using an object to retrieve the value WorkflowParameters.FINDING_TO_MOVE is an enum shouldnt compiler stop and say ...