verbose sort

[bob smith]

From: bob smith <[email protected]>

I have some code that sorts a list like so:

Vector<String> my_list = new Vector<String>();


Comparator<String> c = new Comparator<String>() {
@Override
public int compare(String object1, String object2) {
if (object1 == null)
return -1;
if (object2 == null)
return 1;
object1 = object1.toLowerCase();
object2 = object2.toLowerCase();
return object1.compareTo(object2);
};
};

Collections.sort(my_list, c);


This seems like a lot of code for such a common operation. Is there a more
succinct way of doing this?

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[markspace]

To: bob smith
From: markspace <-@.>

I have some code that sorts a list like so:

Vector<String> my_list = new Vector<String>();


Comparator<String> c = new Comparator<String>() {
@Override
public int compare(String object1, String object2) {
if (object1 == null)
return -1;
if (object2 == null)
return 1;
object1 = object1.toLowerCase();
object2 = object2.toLowerCase();
return object1.compareTo(object2);
};
};

Collections.sort(my_list, c);


This seems like a lot of code for such a common operation.
Is there a more succinct way of doing this?

Collections.sort( my_list, String.CASE_INSENSITIVE_ORDER );

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[Eric Sosman]

To: markspace
From: Eric Sosman <[email protected]>

Collections.sort( my_list, String.CASE_INSENSITIVE_ORDER );

Throws NullPointerException if the list has any nulls.

--
Eric Sosman
(e-mail address removed)

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[markspace]

To: Eric Sosman
From: markspace <-@.>

Throws NullPointerException if the list has any nulls.

That's unfortunate. I thought there were more "pre-made" Comparators, but
couldn't find any. That too bad too, some wrappers would handle a large number
of situations, including null checks.

I really thought there were more Comparators in the API, I might just be
missing them.

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[Volker Borchert]

To: bob smith
From: Eric Sosman <[email protected]>


succinct way of doing this?

Consider using compareToIgnoreCase(). Also, think about what
happens when two null's are compared: You should return zero rather than
declaring one of them "less than" the other, because otherwise your comparator
is inconsistent (you can have A<B, B<C, but C<A).

public int compare(String s1, String s2) {
if (s1 == null)
return s2 == null ? 0 : -1;
return s2 == null ? +1 : s1.compareToIgnoreCase(s2);
}

I'd do it as a fastpath and GoF Decorator

public final class NullFirstComparator<T> implements Comparator<T> {
@NonNull
private final Comparator<T> delegate;

public NullFirstComparator(@NonNull final Comparator<T> delegate) {
this.delegate = delegate;
}

public int compare(final T t1, final T t2) {
if (t1 == t2) {
return 0;
} else if (t1 == null) {
return -1;
} else if (t2 == null) {
return 1;
} else {
return delegate.compare(t1, t2);
}
}
}

Collections.sort(my_list, new NullFirstComparator<String>(String.CASE_INSENSITIVE_ORDER));

 

[Daniel Pitts]

To: markspace
From: Daniel Pitts <[email protected]>

That's unfortunate. I thought there were more "pre-made" Comparators,
but couldn't find any. That too bad too, some wrappers would handle a
large number of situations, including null checks.

I really thought there were more Comparators in the API, I might just be
missing them.

I believe Apache Commons has a bunch of useful generic Comparator
implementations.

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[Lew]

To: bob smith
From: Lew <[email protected]>

I have some code that sorts a list like so:

Vector<String> my_list = new Vector<String>();

Comparator<String> c = new Comparator<String>() {
@Override
public int compare(String object1, String object2) {
if (object1 == null)
return -1;

if (object2 == null)
return 1;

object1 = object1.toLowerCase();
object2 = object2.toLowerCase();

return object1.compareTo(object2);
};
};

Collections.sort(my_list, c);

This seems like a lot of code for such a common operation. Is there a more

succinct way of doing this?

Others have shown ways to shorten this, but I'm curious.

"Seems" - such a duck-and-cover word. You made an assessment. Based on what
criteria?

What is "a lot"?

You could write a cover method.

Apache Commons might have a utility class for that.

--
Lew

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[bob smith]

To: markspace
From: bob smith <[email protected]>

Collections.sort( my_list, String.CASE_INSENSITIVE_ORDER );

Very nice, thanks.

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[Roedy Green]

To: bob smith
From: Roedy Green <[email protected]>

This seems like a lot of code for such a common operation. Is there a more

succinct way of doing this?

see http://mindprod.com/applet/comparatorcutter.html
--
Roedy Green Canadian Mind Products
http://mindprod.com
The greatest shortcoming of the human race is our inability to understand the
exponential function.
~ Dr. Albert A. Bartlett (born: 1923-03-21 age: 89)

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