CODEWITHSUNDEEP
javaset
user2081119
user2081119

Reputation: 321

how to make a Set to be empty

I want to initialize my set to be empty (not null), can anyone help me? Here is my code

public class Graph {
private Set<Vertex> vertices;

public Graph() {
    vertices = {};
}

I know that this is a wrong way to do that, but couldn't do anything else

Upvotes: 0

Views: 612

Answers (4)

Achrome
Achrome

Reputation: 7821

Replace

vertices = {};

With

vertices = new HashSet<Vertex>();

This will initialize an empty HashSet for your Set interface

Upvotes: 1

Brian Agnew
Brian Agnew

Reputation: 272357

Set is an interface. You need to decide on the implementation required, and then construct using a no-args constructor. e.g.

vertices = new HashSet<Vertex>();

or

vertices = new TreeSet<Vertext>();

See this SO question/answer for more info on TreeSet vs HashSet. Given that Set is an interface, any number of implementations could exist (you could even write your own) but I suspect you'll want one of these two to begin with.

Upvotes: 4

Cratylus
Cratylus

Reputation: 54094

public Graph(){  
  vertices = new HashSet<Vertex>();  
}

or 

public Graph(){  
  vertices = new TreeSet<Vertex>();  
}

Upvotes: 1

Greg Kopff
Greg Kopff

Reputation: 16605

You need to execute a constructor:

public Graph() {
  vertices = new HashSet<>();
}

Set is an interface definition, so you will need to pick a concrete implementation of Set. HashSet is one such implementation, but TreeSet is another (TreeSet is actually an implementation of a SortedSet).

Upvotes: 1

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