Sort Arraylist by property of object

Question

So I would like to sort everything out in my ArrayList by using the objects String Name that I have assigned to it.

So far I've read about Comparators to get what I want done. But when I implement it, I get a compile error.

I initialize it like this

private static ArrayList<PeopleInfo> infoArray = new ArrayList<PeopleInfo>();

and call the sort like this

Collections.sort(infoArray, new CustomComparator());

and this is the Class.

public class CustomComparator implements Comparator<PeopleInfo> {
    @Override
    public int compare(PeopleInfo o1, PeopleInfo o2) {
        return o1.GetLast().compareTo(o2.GetLast());
    }
}

The error I get is "No enclosing instance of type mainClass is accessible. Must qualify the allocation with an enclosing instance of type mainClass (e.g. x.new A() where x is an instance of MainClass)."

Not really understanding what's happening. Thanks in advance!

Where are you getting this error?? Where is your PeopleInfo class?? And which is your MainClass?? — Rohit Jain
– Rohit Jain, Commented Oct 6, 2012 at 8:06
Possible duplicate of Java - No enclosing instance of type Foo is accessible — fabian
– fabian, Commented Mar 4, 2016 at 0:25

Sameer · Accepted Answer · 2012-10-06 08:06:31Z

3

Declare your Comparator class as a static class

public static class CustomComparator implements Comparator<PeopleInfo> {

answered Oct 6, 2012 at 8:06

Sameer

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4 Comments

Kelsey Abreu Over a year ago

Gaaah, something so simple. Mind explaining why :)?

clstrfsck Over a year ago

There seems to be a fairly decent explanation here, with links to further info: stackoverflow.com/questions/70324/…

amit Over a year ago

@KelseyAbreu: without the static keyword when declaring an inner class - it (the inner class) must have an "attached" instance of the enclosing class. So, you cannot use it (easily) in static methods (such as main(String[])). When using the static keyword, you let the compiler know it does not need an instance of the enclosing class, and is actually behaving like a normal not nested class.

Kelsey Abreu Over a year ago

Thanks! Some of the most obvious things happen when learning new languages.

Satheesh Cheveri · Accepted Answer · 2012-10-06 09:32:03Z

0

Alternatively you can declare comparator outside main class.

answered Oct 6, 2012 at 9:32

Satheesh Cheveri

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