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Getting default value for java primitive types

I have a java primitive type at hand:

Class c = int.class; // or long.class, or boolean.class

I'd like to get a 'default value' for this class - specifically the value is assigned to fields of this type if they are not initialized. E.g., '0' for a number, 'false' for a boolean.

Is there a generic way to do this? I tried

c.newInstance()

But I'm getting an InstantiationException, and not a default instance.

Google Guava isNullOrEmpty for collections

I see that Guava has isNullOrEmpty utility method for Strings

Strings.isNullOrEmpty(str)

Do we have anything similar for Lists? Something like

Lists.isNullOrEmpty(list)

which should be equivalent to

list == null || list.isEmpty()

Also, do we have anything similar for Arrays? Something like

Arrays.isNullOrEmpty(arr)

which should be equivalent to

arr == null || arr.length == 0

Maven for Eclipse 1.5.0 plugin cannot be installed under Kepler

I downloaded Eclipse Kepler and tried to install M2Eclipse from its update site.

After selecting Maven Integration for Eclipse, I clicked Next and got the following error:

Missing requirement: Maven Integration for Eclipse 1.5.0.20140606-0033 (org.eclipse.m2e.core 1.5.0.20140606-0033) requires 'bundle com.google.guava [14.0.1,16.0.0)' but it could not be found

So I searched through the internet to find out how to install the Guava Eclipse plugin. Some say it's from the Eclipse marketplace, but it cannot be downloaded. I downloaded the binary and tried to copy it to Eclipse's plugin directory. Still the same result.

cp ~/Downloads/guava-16.0.1.jar /Applications/eclipse/plugins/com.google.guava_16.0.1.v1234.jar

How do I install the m2e plugin for Kepler?

Using Google Guava's Objects.ToStringHelper

I used ToStringBuilder.reflectionToString(class) in commons-lang, to implement toString() for simple DTOs. Now I'm trying to use Google Guava instead of Apache commons library. And I found Objects.ToStringHelper in Guava. But it's too verbose if there're lots of members in the class. For example:

@Override
public String toString() {
    return Objects.toStringHelper(this.getClass()).add("name", name)
            .add("emailAddress", emailAddress)
            .add("department", department).add("yearJoined", yearJoined)
            .toString();
}

is much simpler if I use commons-lang:

@Override
public String toString() {
    return ToStringBuilder.reflectionToString(this);
}

Is there any better ways to implement toString() with Guava, not with commons-lang?

Guava: Set + Function = Map?

Is there an idiomatic way to take a Set<K> and a Function<K,V>, and get a Map<K,V> live view? (i.e. the Map is backed by the Set and Function combo, and if e.g. an element is added to the Set, then the corresponding entry also exists in the Map).

(see e.g. Collections2.filter for more discussion on live views)

What if a live view is not needed? Is there something better than this:

public static <K,V> Map<K,V> newMapFrom(Set<K> keys, Function<? super K,V> f) {
    Map<K,V> map = Maps.newHashMap();
    for (K k : keys) {
        map.put(k, f.apply(k));
    }
    return map;
}

Flattening an Iterable> in Guava

Is there a flatten method in Guava - or an easy way to convert an Iterable<Iterable<T>> to an Iterable<T>?

I have a Multimap<K, V> [sourceMultimap] and I want to return all values where the key matches some predicate [keyPredicate]. So at the moment I have:

Iterable<Collection<V>> vals = Maps.filterKeys(sourceMultimap.asMap(), keyPredicate).values();

Collection<V> retColl = ...;
for (Collection<V> vs : vals) retColl.addAll(vs);
return retColl;

I've looked through the Guava docs, but nothing jumped out. I am just checking I've not missed anything. Otherwise, I'll extract my three lines into a short flatten generic method and leave it as that.

Guava: how to combine filter and transform?

I have a collection of Strings, and I would like to convert it to a collection of strings were all empty or null Strings are removed and all others are trimmed.

I can do it in two steps:

final List<String> tokens =
    Lists.newArrayList(" some ", null, "stuff\t", "", " \nhere");
final Collection<String> filtered =
    Collections2.filter(
        Collections2.transform(tokens, new Function<String, String>(){

            // This is a substitute for StringUtils.stripToEmpty()
            // why doesn't Guava have stuff like that?
            @Override
            public String apply(final String input){
                return input == null ? "" : input.trim();
            }
        }), new Predicate<String>(){

            @Override
            public boolean apply(final String input){
                return !Strings.isNullOrEmpty(input);
            }

        });
System.out.println(filtered);
// Output, as desired: [some, stuff, here]

But is there a Guava way of combining the two actions into one step?

initializing a Guava ImmutableMap

Guava offers a nice shortcut way of initializing a map. However I get the following compiler error (Eclipse Indigo) when my map initializer gets to nine entries.

The method of(K, V, K, V, K, V, K, V, K, V) in the type ImmutableMap is not applicable for the arguments (String, String, String, String, String, String, String, String, String, String, String, String, String, String, String, String, String, String)

ImmutableMap<String,String> myMap = ImmutableMap.of(
        "key1", "value1", 
        "key2", "value2", 
        "key3", "value3", 
        "key4", "value4", 
        "key5", "value5", 
        "key6", "value6", 
        "key7", "value7", 
        "key8", "value8", 
        "key9", "value9"
        );

The message appears to say that an ImmutableMap has a maximum size of four pairs of key,value. Obviously, this cannot be the case but I can't figure out what to do to increase the size of my initializer.

Can someone tell me what is missing?

Is there an elegant way to remove nulls while transforming a Collection using Guava?

I have a question about simplifying some Collection handling code, when using Google Collections (update: Guava).

I've got a bunch of "Computer" objects, and I want to end up with a Collection of their "resource id"s. This is done like so:

Collection<Computer> matchingComputers = findComputers();
Collection<String> resourceIds = 
    Lists.newArrayList(Iterables.transform(matchingComputers, new Function<Computer, String>() {
    public String apply(Computer from) {
        return from.getResourceId();
    }
}));

Now, getResourceId() may return null (and changing that is not an option right now), yet in this case I'd like to omit nulls from the resulting String collection.

Here's one way to filter nulls out:

Collections2.filter(resourceIds, new Predicate<String>() {
    @Override
    public boolean apply(String input) {
        return input != null;
    }
});

You could put all that together like this:

Collection<String> resourceIds = Collections2.filter(
Lists.newArrayList(Iterables.transform(matchingComputers, new Function<Computer, String>() {
    public String apply(Computer from) {
        return from.getResourceId();
    }
})), new Predicate<String>() {
    @Override
    public boolean apply(String input) {
        return input != null;
    }
});

But this is hardly elegant, let alone readable, for such a simple task! In fact, plain old Java code (with no fancy Predicate or Function stuff at all) would arguably be much cleaner:

Collection<String> resourceIds = Lists.newArrayList();
for (Computer computer : matchingComputers) {
    String resourceId = computer.getResourceId();
    if (resourceId != null) {
        resourceIds.add(resourceId);
    }
}

Using the above is certainly also an option, but out of curiosity (and desire to learn more of Google Collections), can you do the exact same thing in some shorter or more elegant way using Google Collections?

Interface/enum listing standard mime-type constants

I am looking among the standard libraries (like apache commons, jax, jboss, javax) for an interface or enum that lists the values of all the standard mime-type (aka content-type).

This interface should not be encumbered with too deep with other classes that would make it difficult to include the whole bunch as gwt source code.

for example

interface ContentType{
  String JSON = "Application/JSON";
  blah ... blah ...
}

or,

enum ContentType{
  JSON("Application/JSON"),
  blah ... blah ...
}

Are there tutorials and resources explaining all components of guava-libraries?

I still precise that this request doesn't concern the google-collections part of the library which has a lot of resources: I'm speaking essentially about the services and the concurrency part.

I couldn't find tutorials regarding guava that aren't fully collections oriented. I know the collections are the most important part of the library, but others look interesting while they don't have much associated documentation.

Map implementation with duplicate keys

I want to have Map with duplicate keys, I know there are many Map implementations(eclipse shows me about 50), so I bet there must be one that allows this. I know its easy to write your own Map that does this, but i would rather use some existing solution. Maybe something in commons-collections or google-collections?

Combine multiple Collections into a single logical Collection?

Assume, I have a constant number of collections (e.g. 3 ArrayLists) as members of a class. Now, I want to expose all the elements to other classes so they can simply iterate over all elements (ideally, read only). I'm using guava collections and I wonder how I could use guava iterables/iterators to generate a logical view on the internal collections without making temporary copies.

How to shrink code - 65k method limit in dex

I have a rather large Android app that relies on many library projects. The Android compiler has a limitation of 65536 methods per .dex file and I am surpassing that number.

There are basically two paths you can choose (at least that I know of) when you hit the method limit.

1) Shrink your code

2) Build multiple dex files (see this blog post)

I looked into both and tried to find out what was causing my method count to go so high. The Google Drive API takes the biggest chunk with the Guava dependency at over 12,000. Total libs for Drive API v2 reach over 23,000!

My question I guess is, what do you think I should do? Should I remove Google Drive integration as a feature of my app? Is there a way to shrink the API down (yes, I use proguard)? Should I go the multiple dex route (which looks rather painful, especially dealing with third party APIs)?

Is it a good idea to use Google Guava library for Android development?

I am involved in the development of Android application which is a rather "thick" mobile client for a Web service. It heavily communicates with the server but also has a lot of inner logic too. So, I decided to use some features of Google Guava library to simplify development process. Here is a list of features I'm very interested in: immutable collections, base utils, collection extensions, functional programming sugar and idioms (common.collect and common.base), primitives utilities (common.primitives), hashing utilities (common.hash), concurrent utils (futures and AsyncFunction). Things I don't want to use in Android: common.cache (see question below), common.eventbus (we have better Android specific libs for this, such as Otto), common.io (we can use okio for Android now).

I read that using Guava for Android can significantly slow down compilation process and also decrease the whole runtime performance: Bad performance with Guava Cache (in this case it is reasonable and there is no need to use Guava's cache for Android) and Adding Google Guava to Android project - significantly slows down the build

So, is it efficient to use Guava library in Android project or this library is designed to be used only for the server-side development, and I should go with standard solutions? Any explanations will be very appreciated.