Setting all keys to have the same value by using an iterator

Question

I created a hashmap to represent a graph. The keys in my hash map are the vertices and the values are the edges. From my hashmap I take all of its vertices and store them in a dictionary called vertexDictionary. I would now like to set all the values of the vertex dictionary to False but I am having trouble with this. I tried to use an iterator but I am getting an error in my code with the starred line. My code is below:

public void clearMarks(){
// Sets marks for all vertices to false.
  Set set = graph.entrySet();
  Iterator i = set.iterator();

  while(i.hasNext()) {
    Map.Entry g = (Map.Entry)i.next();
    *this.graph.put(g.getKey(), false);*
  }
}

Is `graph` declared using generics (e.g. `Map graph;`)? If so that line won't compile because you are using raw types. — Paul Boddington, Feb 06 '17 at 02:11
http://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it — Paul Boddington, Feb 06 '17 at 02:11

score 0 · Answer 1 · answered Feb 06 '17 at 02:15

0

The getKey() method returns Object. The problem is that you don't cast it. Let's say your keys are integer, then you should change your code to this:

this.graph.put((int) g.getKey(), false);

answered Feb 06 '17 at 02:15

Thanasis1101

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score 0 · Answer 2 · answered Feb 06 '17 at 02:35

You have a vertexDictionay which contains all the vertices that you are interested in, and for each of those you want to set them to False.

So I assume that you have some data structure like Map<Integer, Boolean> vertexDictionay;

You should be able to

    for (Map.Entry vertex : vertexDictionay.entrySet()) {
        vertex.setValue(false);
    }

The foreach loop uses an iterator under the hood as discussed here. This fixes your argument mismatch error and is more readable IMHO

Setting all keys to have the same value by using an iterator

2 Answers2