This question already has answers here:
What is the point of the diamond operator (<>) in Java?
(7 answers)
Closed 8 years ago.
I'm curious, When declaring ArrayLists, What is the difference in doing this:
List<String> arrayList1= new ArrayList<String>();
and this:
List<String> arrayList2= new ArrayList<>();
i.e. not declaring the <String> twice?
the only difference is that the first form is compatible with earlier java versions than java 7.
And you don't need the <> either in latter versions. e.g
List<String> arrayList2= new ArrayList();
Related
This question already has answers here:
What does it mean to program to an interface?
(17 answers)
Arraylist and List in Java
(3 answers)
Closed 7 months ago.
I am wondering about the difference between these two options to create a list of string. Which one to use when creating a list in Java?
Option 1
List<String> list1 = new ArrayList<String>();
Option 2
ArrayList<String> list2 = new ArrayList<String>();
This question already has answers here:
Creating an array of objects in Java
(9 answers)
Closed 7 years ago.
I don't recognize this kind of form Java syntax for constructor - granted I do very little Java now (taken from there):
new PersistentArrayMap(new Object[]{formKey, form});
I was expecting something along the lines of new Object(...) as parameter. Could someone decompose the above line ?
You are creating new Object array Object[] initialised to {obj1, obj2}
It is a way of declaring and initializing an array in java. A simpler example is the following:
int[] myIntArray = new int[]{1,2,3};
This question already has answers here:
What is the point of the diamond operator (<>) in Java?
(7 answers)
Closed 7 years ago.
I'm using Android Studio and I write this :
List<Button> buttons = new ArrayList<Button>();
I have this message :
Explicit type argument Button should be replaced by <>
I'm curious, why would it be better to use diamond instead ?
List<Button> buttons = new ArrayList<>();
EDIT :
I don't agree with the duplicate at all ! I saw that answer before and it compares explicit argument to no argument at all, whereas I compare explicit argument to implicit argument !
It is less verbose, consider the following
Map<String,List<String>> map = new HashMap<String,List<String>>();
vs
Map<String,List<String>> map = new HashMap<>();
I think you would go for the second option
This question already has answers here:
What is the point of the diamond operator (<>) in Java?
(7 answers)
Closed 7 years ago.
I've Googled around but I can't find the use for the <> in ArrayList or List. I know how to use ArrayList but I like to know how things work as well. What are the <> for? I figure it's like an argument of sorts since it specifies the type but it's not an argument since it doesn't go in () so what do the <> mean?
to specify the generic type.
List<String> strings = new ArrayList<String>(); will restrict only strings to be added
When you say List strings = new ArrayList(); you are not specifying which kind of object the strings list accepts. So, strings.add(new Object()) is also possible. By specifying List<String> strings = new ArrayList<String>(); you restrict the arraylist to access only String elements.
This question already has answers here:
How to create array of unique object list in Swift
(11 answers)
Closed 8 years ago.
I have specific logic in Java that uses HashSet<String>. Set collection contains only unique items.
For example:
Set<String> mySets = new HashSet<String>();
mySets.add("a");
mySets.add("a");
mySets.add("b");
mySets.add("a");
I get: ["a","b"].
What is equivalent collection in Swift?
Thanks,
The Swift to Java's HashSet is Set.
Example:
var s = Set<Character>()
s.insert("a")
s.insert("a")
s.insert("b")
s.insert("a")
print("s: \(s)")
output:
s: ["b", "a"]
Official docs