According to the [Java specification][1] that would be for example:

    Collections.&lt;String&gt;unmodifiableSet()

(Sorry for asking and answering my own question - I was just looking this up for the third time. :-)

  [1]: http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.12

The following is **not** the syntax 

    &lt;ArgType&gt;genericMethod()

It seems the type arguments **must** come after a dot as in

    SomeClass.&lt;ArgType&gt;genericMethod()
    this.&lt;ArgType&gt;genericMethod()
    p.&lt;ArgType&gt;genericMethod()
    super.&lt;ArgType&gt;genericMethod()
    SomeClass.super.&lt;ArgType&gt;genericMethod()
    SomeClass.this.&lt;ArgType&gt;genericMethod()

A good example from `java.util.Collection` of specifying a generic method which defines its own generic type is [`Collection.toArray`][1] where the method signature looks like:

    &lt;T&gt; T[] toArray(T[] a);

This declares a generic type T, which is defined on method call by the parameter `T[] a` and returns an array of T&#39;s.  So the same instance could call the toArray method in a generic fashion:

    Collection&lt;Integer&gt; collection = new ArrayList&lt;Integer&gt;();
    collection.add(1);
    collection.add(2);

    // Call generic method returning Integer[]
    Integer[] ints = collection.toArray(new Integer[]{});

    // Call generic method again, this time returning an Number[] (Integer extends Number)
    Number[] nums = collection.toArray(new Number[]{});

Also, see the [java tutorial on generic type parameters][2].


  [1]: http://java.sun.com/javase/6/docs/api/java/util/Collection.html#toArray%28T[]%29
  [2]: http://java.sun.com/docs/books/tutorial/extra/generics/methods.html

What are the different ways where we can use object operators `-&gt;` in PHP?


Where do we use the object operator &quot;-&gt;&quot; in PHP?

In Bash, I want to get the Nth word of a string hold by a variable.

For instance:

    STRING=&quot;one two three four&quot;
    N=3

Result:

    &quot;three&quot;


What Bash command/script could do this?

Nth word in a string variable

What is the syntax for explicitly giving the type parameters for a generic Java method?

Java-syntax for explicitly specifying generic arguments in method calls

<p>What is the syntax for explicitly giving the type parameters for a generic Java method?</p>


When I start Tomcat I get the following error:

    Jun 10, 2010 5:17:25 PM org.apache.catalina.core.StandardContext start
    SEVERE: Error filterStart
    Jun 10, 2010 5:17:25 PM org.apache.catalina.core.StandardContext start
    SEVERE: Context [/mywebapplication] startup failed due to previous errors

It seems odd that the logs for Tomcat would not include a stack trace.  Does somebody have a suggestion for how to increase the logging in Tomcat to get stack traces for errors like this?

Tomcat startup logs - SEVERE: Error filterStart how to get a stack trace?

When I run `maven install` on my multi module maven project I always get the following output:

    [WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!

So, I googled around a bit, but all I can find is that I have to add:

    &lt;properties&gt;
        &lt;project.build.sourceEncoding&gt;UTF-8&lt;/project.build.sourceEncoding&gt;
    &lt;/properties&gt;

...to my pom.xml. But it&#39;s already there (in the parent `pom.xml`).

Configuring `&lt;encoding&gt;` for the maven-resources-plugin or the maven-compiler-plugin also doesn&#39;t fix it. 

So what&#39;s the problem?

How to configure encoding in Maven?

What does `assert` do?
For example in the function:

    private static int charAt(String s, int d) {
    	assert d &gt;= 0 &amp;&amp; d &lt;= s.length();
    	if (d == s.length()) return -1;
    	return s.charAt(d);
    }

What does the &quot;assert&quot; keyword do?

I often have a need to take a list of objects and group them into a Map based on a value contained in the object. Eg. take a list of Users and group by Country.

My code for this usually looks like:

    Map&lt;String, List&lt;User&gt;&gt; usersByCountry = new HashMap&lt;String, List&lt;User&gt;&gt;();
    for(User user : listOfUsers) {
    	if(usersByCountry.containsKey(user.getCountry())) {
    		//Add to existing list
    		usersByCountry.get(user.getCountry()).add(user);
    
    	} else {
    		//Create new list
    		List&lt;User&gt; users = new ArrayList&lt;User&gt;(1);
    		users.add(user);
    		usersByCountry.put(user.getCountry(), users);
    	}
    }

However I can&#39;t help thinking that this is awkward and some guru has a better approach. The closest I can see so far is the [MultiMap from Google Collections][1]. 

Are there any standard approaches?

Thanks!


  [1]: http://google-collections.googlecode.com/svn/trunk/javadoc/index.html?com/google/common/collect/Multimap.html

Shortcut for adding to List in a HashMap

When creating JSON data manually, how should I escape string fields? Should I use something like Apache Commons Lang&#39;s `StringEscapeUtilities.escapeHtml`, `StringEscapeUtilities.escapeXml`, or should I use `java.net.URLEncoder`?

The problem is that when I use `SEU.escapeHtml`, it doesn&#39;t escape quotes and when I wrap the whole string in a pair of `&#39;`s, a malformed JSON will be generated.


How should I escape strings in JSON?

This is more of a documentation than a real question. This does not seem to have been addressed on SO yet (unless I missed it), so here goes:

Imagine a generic class that contains a static member:

    class Foo&lt;T&gt; {
        public static int member;
    }

Is there a new instance of the member for each specific class, or is there only a single instance for all Foo-type classes?

It can easily be verified by code like this:

    Foo&lt;int&gt;.member = 1;
    Foo&lt;string&gt;.member = 2;
    Console.WriteLine (Foo&lt;int&gt;.member);

What is the result, and where is this behavior documented?

Are static members of a generic class tied to the specific instance?

I have done far more C++ programming than &quot;plain old C&quot; programming.  One thing I sorely miss when programming in plain C is type-safe generic data structures, which are provided in C++ via templates.

For sake of concreteness, consider a generic singly linked list.  In C++, it is a simple matter to define your own template class, and then instantiate it for the types you need.

In C, I can think of a few ways of implementing a generic singly linked list:

1. Write the linked list type(s) and supporting procedures once, using void pointers to go around the type system.
2. Write preprocessor macros taking the necessary type names, etc, to generate a type-specific version of the data structure and supporting procedures.
3. Use a more sophisticated, stand-alone tool to generate the code for the types you need.

I don&#39;t like option 1, as it is subverts the type system, and would likely have worse performance than a specialized type-specific implementation.  Using a uniform representation of the data structure for all types, and casting to/from void pointers, so far as I can see, necessitates an indirection that would be avoided by an implementation specialized for the element type.

Option 2 doesn&#39;t require any extra tools, but it feels somewhat clunky, and could give bad compiler errors when used improperly.

Option 3 could give better compiler error messages than option 2, as the specialized data structure code would reside in expanded form that could be opened in an editor and inspected by the programmer (as opposed to code generated by preprocessor macros).  However, this option is the most heavyweight, a sort of &quot;poor-man&#39;s templates&quot;.  I have used this approach before, using a simple sed script to specialize a &quot;templated&quot; version of some C code.

I would like to program my future &quot;low-level&quot; projects in C rather than C++, but have been frightened by the thought of rewriting common data structures for each specific type.

What experience do people have with this issue?  Are there good libraries of generic data structures and algorithms in C that do not go with Option 1 (i.e. casting to and from void pointers, which sacrifices type safety and adds a level of indirection)?

Type-safe generic data structures in plain-old C?

I would like a method that takes a `List&lt;T&gt;` where `T` implements `Comparable` and returns `true` or `false` depending on whether the list is sorted or not.

What is the best way to implement this in Java?  It&#39;s obvious that generics and wildcards are meant to be able to handle such things easily, but I&#39;m getting all tangled up.

It would also be nice to have an analogous method to check if the list is in reverse order.


How to determine if a List is sorted in Java?

So, I have a class with a constructor like this:

    public FilterList(Set&lt;Integer&gt; labels) {
        ...
    }

and I want to construct a new `FilterList` object with an empty set. Following Joshua Bloch&#39;s advice in his book Effective Java, I don&#39;t want to create a new object for the empty set; I&#39;ll just use `Collections.emptySet()` instead:

    FilterList emptyList = new FilterList(Collections.emptySet());

This gives me an error, complaining that `java.util.Set&lt;java.lang.Object&gt;` is not a `java.util.Set&lt;java.lang.Integer&gt;`. OK, how about this:

    FilterList emptyList = new FilterList((Set&lt;Integer&gt;)Collections.emptySet());

This also gives me an error! Ok, how about this:

    Set&lt;Integer&gt; empty = Collections.emptySet();
    FilterList emptyList = new FilterList(empty);

Hey, it works! But why? After all, Java doesn&#39;t have type inference, which is why you get an unchecked conversion warning if you do `Set&lt;Integer&gt; foo = new TreeSet()` instead of `Set&lt;Integer&gt; foo = new TreeSet&lt;Integer&gt;()`. But `Set&lt;Integer&gt; empty = Collections.emptySet();` works without even a warning. Why is that?

Why does using Collections.emptySet() with generics work in assignment but not as a method parameter?

This is a bit of noob question - I&#39;m still fairly new to C# and generics and completely new to predicates, delegates and lambda expressions...

I have a class &#39;Enquiries&#39; which contains a generic list of another class called &#39;Vehicles&#39;. I&#39;m building up the code to add/edit/delete Vehicles from the parent Enquiry. And at the moment, I&#39;m specifically looking at deletions.

From what I&#39;ve read so far, it appears that I can use Vehicles.RemoveAll() to delete an item with a particular VehicleID or all items with a particular EnquiryID. My problem is understanding how to feed .RemoveAll the right predicate - the examples I have seen are too simplistic (or perhaps I am too simplistic given my lack of knowledge of predicates, delegates and lambda expressions).

So if I had a `List&lt;Of Vehicle&gt; Vehicles` where each Vehicle had an `EnquiryID`, how would I use `Vehicles.RemoveAll()` to remove all vehicles for a given EnquiryID?

I understand there are several approaches to this so I&#39;d be keen to hear the differences between approaches - as much as I need to get something working, this is also a learning exercise.

As an supplementary question, is a Generic list the best repository for these objects? My first inclination was towards a Collection, but it appears I am out of date. Certainly Generics seem to be preferred, but I&#39;m curious as to other alternatives.


Content Type	Original Author	Original Content on Stackoverflow
Question	Hans-Peter Störr	View Question on Stackoverflow
Solution 1 - Java	Hans-Peter Störr	View Answer on Stackoverflow
Solution 2 - Java	Theodore Norvell	View Answer on Stackoverflow
Solution 3 - Java	krock	View Answer on Stackoverflow

Java-syntax for explicitly specifying generic arguments in method calls

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Nth word in a string variable

Where do we use the object operator "->" in PHP?

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