I Use Generics, But Not This Class<T> thing!

I am trying to call this method to concat two arrays using Google Collections

public stat开发者_JAVA技巧ic <T> T[] concat(T[] first,
                             T[] second,
                             Class<T> type)

It's returning empty results. I am using

ObjectArrays.concat(array1, array2, Blah.class)

which is the only thing that compiles.

array1 and array2 are of type Blah[].

What's the right syntax?

Bonus question: do other collections libraries have documentation with examples?

Edit: Problem was my bone-headed code.

public void register(ButtonPair[] pairs) {
    pairs = ObjectArrays.concat(this.pairs, pairs, ButtonPair.class);
}

the right side of the thing is okay, but the left side is not assigning to this.pairs due to the ambiguity. Sorry! And hats off to Google Collections!

The following worked for me:

String[] arr1 = { "abc", "def" };
String[] arr2 = { "ghi", "jkl" };
String[] result = ObjectArrays.concat(arr1, arr2, String.class);

How are you getting the result from concat()?

For some example usage of the Google Collections classes, check out the unit tests.

For example:

String[] result = ObjectArrays.concat(
    new String[] { "a", "b" }, new String[] { "c", "d" }, String.class);
assertEquals(String[].class, result.getClass());
assertContentsInOrder(Arrays.asList(result), "a", "b", "c", "d");

So, what the Class<T> notation means is that it needs you to specify what class the objects in the other two argument arrays belong to.

Your syntax looks totally correct. I think the problem must be elsewhere. Are you 100% certain about the input values? Here is a test case:

import com.google.common.collect.ObjectArrays;

public class ObjectArrayTest
{
    public static void main(String[] args)
    {
        String[] first = new String[] { "Fire", "Earth" };
        String[] second = new String[] { "Water", "Air" };

        String[] result = ObjectArrays.concat(first, second, String.class);

        for (String s : result)
        {
            System.out.println (s);
        }
    }
}

Isn't this because you are not assigning the result to the instance variable but to the method variable.

That is this:

public void register(ButtonPair[] pairs) {
    pairs = ObjectArrays.concat(this.pairs, pairs, ButtonPair.class);
    }

should be

public void register(ButtonPair[] pairs) {
    this.pairs = ObjectArrays.concat(this.pairs, pairs, ButtonPair.class);
    }

Incidentally, this is why at our shop we have have a different naming convention for method parameters and variables than that for instance variables (though not the awful prefixing/suffixing of instance variables like _someInstanceVar).