LinkedHashMap searching

Question

I have a class

class polygon
{
    private String name;
    private int quantity;

    // default constructor
    private polygon()
    { }

    public String get name() {
        return name;
    }
    public void setname(String name) {
        this.name = name;
    }

    public int getquantity() {
        return quantity;
    }
    public void setquantity(int quantity) {
        this.quantity = quantity;
    }       
}

and also I have a map like this:

LinkedHashMap<Integer, polygon> polymap = new LinkedHashMap<Integer, polygon>();

I have to ask two questions:

1. How can I find if there is a member with specific value which has the name like "square"?
2. How can I get all the member with the lowest quantity?

Thanks.

Answer 1

What we have learned from comments and updates: Polygon is a class with members String name (possibly but not necessarily unique) and int quantity (no restriction). There is also a timestamp, and this Integer is used as a key in the

Map<Integer,Polygon> polymap

To find all Polygons with a given name:

for( Polygon polygon: polymap.values() ){
    if( polygon.getName().equals( givenName ) ){ //... }
}

Now this is a sequential search and may take some time if the number of entries is very big. Assuming names are unique, O(1) access time can be achieved by creating another Map in parallel to polymap, mapping name strings to Polygon objects. (Consider the additional effort for removing, but Map.remove( ., . ) should help.)

To find all Polygons with the minimum quantity, determine the minimum while keeping a set of the Polygons with that minimum:

int min = Integer.MAX_VALUE;
Set<Polygon> polyset = new HashSet<>();
for( Polygon polygon: polymap.values() ){
    int qtty = polygon.getQuantity();
    if( qtty < min ){
        min = qtty;
        polyset.clear();
        polyset.add( polygon );
    } else if( qtty == min ){
        polyset.add( polygon );
    }
}

Again, a sequential search, but here a second map will require a multimap, i.e., a Map<Integer,Collection<Polygon>>.

Answer 2

LinkedHashMap<Integer, polygon> polymap = new LinkedHashMap<Integer, polygon>();

1. How can I find if there is a member with specific value which has the name like "square"?

The containsValue() uses equals method for find the match. You can override the equals() method of the polygon class. Then you can use the containsValue(new polygon()) to find whether the value exist or not. The equals method implementation will be completely depended on the name field of the polygon class. Something like this:

@Override
public boolean equals(Object o) {
  if (this == o) return true;
  if (!(o instanceof polygon)) return false;

  polygon polygon = (polygon) o;

  if (!name.equals(polygon.name)) return false;

  return true;
}

Note: You are overriding the equals() method of the class, so could have some side affects on how you are using it at other places in your application.

2. How can I get all the member with the lowest quantity?

I would suggest you maintain a separate PriorityQueue for finding lowest quantity polygon. Provide a custom Comparator while initializing the queue.