For example, package main import “fmt” func main() { type Map1 map[string]interface{} type Map2 map[string]int m := Map1{“foo”: Map2{“first”: 1}, “boo”: Map2{“second”: 2}} //m = map[foo:map[first: 1] boo: map[second: 2]] fmt.Println(“m:”, m) for k, v := range m { fmt.Println(“k:”, k, “v:”, v) } } Output: m: map[boo:map[second:2] foo:map[first:1]] k: boo v: map[second:2] k: foo … Read more
It’s always better to copy using a copy constructor. clone() in Java is broken (see SO: How to properly override clone method?). Josh Bloch on Design – Copy Constructor versus Cloning If you’ve read the item about cloning in my book, especially if you read between the lines, you will know that I think clone … Read more
Use len(m). From http://golang.org/ref/spec#Length_and_capacity len(s) string type string length in bytes [n]T, *[n]T array length (== n) []T slice length map[K]T map length (number of defined keys) chan T number of elements queued in channel buffer Here are a couple examples ported from the now-retired SO documentation: m := map[string]int{} len(m) // 0 m[“foo”] = … Read more
You can use the Google Collections API for that, recently renamed to Guava, specifically a BiMap A bimap (or “bidirectional map”) is a map that preserves the uniqueness of its values as well as that of its keys. This constraint enables bimaps to support an “inverse view”, which is another bimap containing the same entries … Read more
I believe you’re looking for zipWithIndex? scala> val ls = List(“Mary”, “had”, “a”, “little”, “lamb”) scala> ls.zipWithIndex.foreach{ case (e, i) => println(i+” “+e) } 0 Mary 1 had 2 a 3 little 4 lamb From: http://www.artima.com/forums/flat.jsp?forum=283&thread=243570 You also have variations like: for((e,i) <- List(“Mary”, “had”, “a”, “little”, “lamb”).zipWithIndex) println(i+” “+e) or: List(“Mary”, “had”, “a”, “little”, … Read more
Map <Integer, Point2D.Double> hm = new HashMap<Integer, Point2D>(); hm.put(1, new Point2D.Double(50, 50));
An unmodifiable map may still change. It is only a view on a modifiable map, and changes in the backing map will be visible through the unmodifiable map. The unmodifiable map only prevents modifications for those who only have the reference to the unmodifiable view: Map<String, String> realMap = new HashMap<String, String>(); realMap.put(“A”, “B”); Map<String, … Read more
The map::operator[] searches the data structure for a value corresponding to the given key, and returns a reference to it. If it can’t find one it transparently creates a default constructed element for it. (If you do not want this behaviour you can use the map::at function instead.) You can get a full list of … Read more
They are implemented in very different ways. hash_map (unordered_map in TR1 and Boost; use those instead) use a hash table where the key is hashed to a slot in the table and the value is stored in a list tied to that key. map is implemented as a balanced binary search tree (usually a red/black … Read more
Like this: <c:forEach var=”entry” items=”${myMap}”> Key: <c:out value=”${entry.key}”/> Value: <c:out value=”${entry.value}”/> </c:forEach>