Hash Map Query

[Marie O' Driscoll]

Hi,

I am editing open source code. A hash map is defined as follows:

Map<String, Junction> junctions = new HashMap<String, Junction>();
//read in values from xml
Junction junction = new Junction(id, x, y);
junctions.put(id, junction);

Junction is a class with a string id and two float values - x and y. In a subsequent class i need to access the values in the hash map. I have the following but I'm getting NULL values: Can someone please point out how I should retrieve class info from the hash map?

for (int attr = 0; attr < junctions.size(); attr++) 
	out.println("$junction_(" + junctions.get(junction).id + ") " + "setdest " + junctions.get(junction).x + " " + junctions.get(junction).y + "\"");

I also tried the following but it didn't work either:

for (int attr = 0; attr < junctions.size(); attr++) 
	out.println("$junction_(" + junctions.get("id" + ") " + "setdest " + junctions.get("x") + " " + junctions.get("y") + "\"");

Many thanks in advance

[Sebastian Janisch]

like this

for (String junction : junctions.keySet())
{
    System.out.println(junctions.get(junction));
}

Also, using public instance fields is horrid. make id, x, y private and create accessor and mutator methods.

[Rob Spoor]

Besides keySet() which returns all the keys, there are also methods values() which returns the values and entrySet() which returns both:

for (Junction junction: junctions.values())
{
    System.out.println(junction);
}
for (Map.Entry<String, Junction> entry: junctions.entrySet())
{
    System.out.println(entry.getKey() + ": " + entry.getValue());
}

Prefer using either values() if you don't need the keys or entrySet() if you do need the keys inside your loop body. Using entrySet() is faster than using keySet() and get() since you don't need to do a full lookup - the value is already there.

[Marie O' Driscoll]

Thanks for both replies - Problem solved!