collections
How to convert int[] into List in Java?
There is no shortcut for converting from int[] to List<Integer> as Arrays.asList does not deal with boxing and will just create a List<int[]> which is not what you want. You have to make a utility method.
Printing HashMap In Java
keySet() only returns a set of keys from your hash map, you should iterate this key set and the get the value from the hash map using these keys. In your example, the type of the hash map’s key is TypeKey, but you specified TypeValue in your generic for-loop, so it cannot be compiled. You should change it to: Update … Read more
How to convert List to int[] in Java?
Unfortunately, I don’t believe there really is a better way of doing this due to the nature of Java’s handling of primitive types, boxing, arrays and generics. In particular: List<T>.toArray won’t work because there’s no conversion from Integer to int You can’t use int as a type argument for generics, so it would have to be an int-specific method (or one which used reflection to do … Read more
Java Ordered Map
The SortedMap interface (with the implementation TreeMap) should be your friend. The interface has the methods: keySet() which returns a set of the keys in ascending order values() which returns a collection of all values in the ascending order of the corresponding keys So this interface fulfills exactly your requirements. However, the keys must have a meaningful order. Otherwise you … Read more
Why is there no SortedList in Java?
List iterators guarantee first and foremost that you get the list’s elements in the internal order of the list (aka. insertion order). More specifically it is in the order you’ve inserted the elements or on how you’ve manipulated the list. Sorting can be seen as a manipulation of the data structure, and there are several ways … Read more
C# Set collection?
Try HashSet: The HashSet(Of T) class provides high-performance set operations. A set is a collection that contains no duplicate elements, and whose elements are in no particular order… The capacity of a HashSet(Of T) object is the number of elements that the object can hold. A HashSet(Of T) object’s capacity automatically increases as elements are added to the object. … Read more
Difference between HashSet and HashMap?
They are entirely different constructs. A HashMap is an implementation of Map. A Map maps keys to values. The key look up occurs using the hash. On the other hand, a HashSet is an implementation of Set. A Set is designed to match the mathematical model of a set. A HashSet does use a HashMap to back its implementation, as you noted. However, it implements an entirely different interface. … Read more
How to sort an ArrayList?
That will do what you want. Remember to import Collections though!
Is there a short contains function for lists?
You can use this syntax: Also, inverse operator: It works fine for lists, tuples, sets and dicts (check keys). Note that this is an O(n) operation in lists and tuples, but an O(1) operation in sets and dicts.