Selecting certain data from ArrayList

Question

I wondering if there is anyway that if I know one part of an ArryList that I can find out the other. The problem I'm running into is my limited knowledge of java.

I have the list set up as:

spotsList = new ArrayList<HashMap<String, String>>();

The activity goes through and adds every spot(from a server) to the list in a forloop with PID and NAME as:

HashMap<String, String> map = new HashMap<String, String>();
                    map.put(TAG_PID, id);
                    map.put(TAG_NAME, name);
spotsList.add(map);

Now is there a way I can get the name if I know the PID?

Thank you in advance,

Tyler

assylias · Accepted Answer · 2014-01-28 22:52:50Z

3

It seems that you expect the PIDs to be unique (given a PID you can find the corresponding name). So instead of a list of maps you should probably just use one map:

Map<String, String> map = new HashMap<String, String>();
for (Spot s : spots) map.put(s.id, s.name);

Retrieving a name from the pid is then simply a matter of:

String name = map.get(pid);

answered Jan 28, 2014 at 22:52

assylias

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3 Comments

TylerM Over a year ago

Thanks :D But when I posted the problem I simplified it by only using name and PID but 6 others that I would need to add to it. Would I go about that the same way?

assylias Over a year ago

The more specific your question, the best answers you will get! If all fields are linked to the pid, you could create a class that wraps the 6 fields and use a Map<String, YourClass> instead.

TylerM Over a year ago

I tried using the class from below but got the error when I changed map<spot> to map<String,spot> even though it was saying it needed more variables there.

Mike B · Accepted Answer · 2014-01-29 06:50:44Z

1

You should probably use a domain class instead of a HashMap to hold that data. If you did that you could easily search a collection for a particular value.

public class Spot {
    private final String pid;
    private final String name;

    public Spot(String pid, String name) {
        this.pid = pid;
        this.name = name;
    }

    // getters 
}

You'll want to add override equals() and hashCode() also.

And then use a map instead of a list:

Map<String,Spot> spots = new HashMap<String,Spot>();
spots.put(pid, new Spot(pid, name));

Then to find one:

Spot spot = spots.get(pid);

edited Jan 29, 2014 at 6:50

answered Jan 28, 2014 at 23:05

Mike B

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7 Comments

TylerM Over a year ago

Thank you, but it underlines map and hashmap saying incorrect number of arguments. Also, how would I go about adding an override for equals() and hashcode()?

Mike B Over a year ago

Make sure you import them first. For equals() and hashCode() check out the builders from Apache Commons: commons.apache.org/proper/commons-lang/apidocs/org/apache/… and commons.apache.org/proper/commons-lang/apidocs/org/apache/…

Mike B Over a year ago

The Map and HashMap. If you did and you're still getting errors, what jdk version are you using?

TylerM Over a year ago

Both are imported. How do I check jdk? I'm just using eclipse and don't remember changing the jdk so I guess the default

TylerM Over a year ago

I also tried using map<string, spot> instead of just <spot> but that did not work either

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