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Java generics warnings on java.util.Collections

I have a method:

public List<Stuff> sortStuff(List<Stuff> toSort) { java.util.Collections.sort(toSort); return toSort; }

This raises a warning:

 Type safety: Unchecked invocation sort(List<Stuff>) of the generic method sort(List<T>) of type Collections.

Eclipse says the only way to fix the warning is to add @SuppressWarnings("unchecked") to my sortStuff method. This seems like a meek way to do something that is built into Java.

Is this really my only option here? Why or why not? Thanks in advance!

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4 answers

Collections.sort(List<T>) expects T to implement Comparable<? super T> Comparable<? super T> . It seems that Stuff implements Comparable , but does not provide a generic type argument.

Be sure to declare this:

 public class Stuff implements Comparable<Stuff>

Instead of this:

 public class Stuff implements Comparable
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Use this:

 // Bad Code public class Stuff implements Comparable{ @Override public int compareTo(Object o) { // TODO return ... } }

or that?

 // GoodCode public class Stuff implements Comparable<Stuff>{ @Override public int compareTo(Stuff o) { // TODO return ... } }
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You will need to change the type of the returned method

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Sort shared collections

This class defines two sorting functions, shown below:

 public static <T extends Comparable<? super T>> void sort(List<T> list); public static <T> void sort(List<T> list, Comparator<? super T> c);

None of them are easy on the eyes, and both include a wildcard (?) Operator in their definitions. The first version only accepts a list if T extends Comparable directly or a generic Comparable instance that accepts T or a superclass as a generic parameter. The second version accepts a list and a comparator created using T or a supertype.

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