Just use Map#get(key) ? Object value = map.get(myCode); Here’s a tutorial about maps, you may find it useful: https://docs.oracle.com/javase/tutorial/collections/interfaces/map.html. Edit: you edited your question with the following: I’m expecting to see a String, such as “ABC” or “DEF” as that is what I put in there initially, but if I do a System.out.println() I get … Read more
ICollection<T> is an interface that exposes collection semantics such as Add(), Remove(), and Count. Collection<T> is a concrete implementation of the ICollection<T> interface. IList<T> is essentially an ICollection<T> with random order-based access. In this case you should decide whether or not your results require list semantics such as order based indexing (then use IList<T>) or … Read more
hashMap.keySet().toArray(); // returns an array of keys hashMap.values().toArray(); // returns an array of values Edit It should be noted that the ordering of both arrays may not be the same, See oxbow_lakes answer for a better approach for iteration when the pair key/values are needed.
First, let’s see what this does: Arrays.asList(ia) It takes an array ia and creates a wrapper that implements List<Integer>, which makes the original array available as a list. Nothing is copied and all, only a single wrapper object is created. Operations on the list wrapper are propagated to the original array. This means that if … Read more
Use List.subList: import java.util.*; import static java.lang.Math.min; public class T { public static void main( String args[] ) { List<String> items = Arrays.asList(“1”); List<String> subItems = items.subList(0, min(items.size(), 2)); // Output: [1] System.out.println( subItems ); items = Arrays.asList(“1”, “2”, “3”); subItems = items.subList(0, min(items.size(), 2)); // Output: [1, 2] System.out.println( subItems ); } } You … Read more
More modern solution Unless you need the internal collection to be mutable, you could use the System.Collections.Immutable package, change your field type to be an immutable collection, and then expose that directly – assuming Foo itself is immutable, of course. Updated answer to address the question more directly Is there any reason to expose an … Read more
var list = new List<string> { “One”, “Two”, “Three” }; Essentially the syntax is: new List<Type> { Instance1, Instance2, Instance3 }; Which is translated by the compiler as List<string> list = new List<string>(); list.Add(“One”); list.Add(“Two”); list.Add(“Three”);
No, this seems perfectly reasonable. There is a List<T>.AddRange() method that basically does just this, but requires your collection to be a concrete List<T>.
Looking at the Java API Specification for the Iterator interface, there is an explanation of the differences between Enumeration: Iterators differ from enumerations in two ways: Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics. Method names have been improved. The bottom line is, both Enumeration and … Read more
The question is (now) about storing lots of data, which can be represented using primitive types like int, in a Map. Some of the answers here are very misleading in my opinion. Let’s see why. I modified the benchmark from trove to measure both runtime and memory consumption. I also added PCJ to this benchmark, … Read more