I tend to prefer the use of `@Override` in this case, so that the method gets flagged in the subclasses if the superclass changes (either removing the method altogether, or changing its signature, etc.).

The only real difference is that without the annotation, if the method in the superclass/interface is changed or removed, the implementation in question simply becomes a &quot;normal&quot; method of that class.  Thus you should add the annotation if you&#39;re implementing the method solely to fulfil the contract; and you probably shouldn&#39;t add it if the method makes sense in your class regardless of any implemented interfaces or inherited abstract methods.

Yes - again, it tells the compiler, &quot;I really want to be overriding a method here. If there *isn&#39;t* a corresponding method to override, I&#39;ve made a mistake and want to be told about it!&quot;

Personally I think it&#39;s a pity that this is just an annotation rather than part of the language (as it is in C#) but that&#39;s the benefit of hindsight, of course.

Yes. It is recommended practise by Joshua Bloch in Effective Java.

Actually, Joshua Bloch, in the final paragraph of page 178 in *Effective Java (2nd Ed.)*, says that it&#39;s not essential for methods of concrete classes that override abstract methods to use the `Override` annotation because the compiler would give an error anyway. However, &quot;it is not harmful to do so&quot;.

I&#39;d recommend choosing a strategy and sticking with it consistently.

Ruby is slow at certain things.  But what parts of it are the most problematic?

How much does the garbage collector affect performance?  I know I&#39;ve had times when running the garbage collector alone took several seconds, especially when working with OpenGL libraries.

I&#39;ve used matrix math libraries with Ruby that were particularly slow.  Is there an issue with how ruby implements basic math?

Are there any dynamic features in Ruby that simply cannot be implemented efficiently?  If so, how do other languages like Lua and Python solve these problems?

Has there been recent work that has significantly improved performance?


What makes Ruby slow?

I have a Perl script that is counting the number of occurrences of various strings in a text file. I want to be able to check if a certain string is not yet a key in the hash. Is there a better way of doing this altogether?

Here is what I am doing:

    foreach $line (@lines){
        if(($line =~ m|my regex|) )
        {
            $string = $1;
            if ($string is not a key in %strings) # &quot;strings&quot; is an associative array
            {
                $strings{$string} = 1;
            }
            else
            {
                $n = ($strings{$string});
                $strings{$string} = $n +1;
            }
        }
    }


How can I see if a Perl hash already has a certain key?

When overriding a non-virtual method in Java, use of the `@Override` annotation is recommended, but what if I implement an abstract method? Should I use `@Override` then as well?

Should I add an @Override annotation when implementing abstract methods in Java?

<p>When overriding a non-virtual method in Java, use of the <code>@Override</code> annotation is recommended, but what if I implement an abstract method? Should I use <code>@Override</code> then as well?</p>


Is UTF-8 the default encoding in Java?  
If not, how can I know which encoding is used by default?

What is the default encoding of the JVM?

The problem is that, as you know, there are thousands of characters [in the Unicode chart][1] and I want to convert all the similar characters to the letters which are in English alphabet.

For instance here are a few conversions:

    ҥ-&gt;H
    Ѷ-&gt;V
    Ȳ-&gt;Y
    Ǭ-&gt;O
    Ƈ-&gt;C
    tђє Ŧค๓เℓy --&gt; the Family
    ...

and I saw that there are more than 20 versions of letter A/a. and I don&#39;t know how to classify them. They look like needles in the haystack. 



The complete list of unicode chars is at [http://www.ssec.wisc.edu/~tomw/java/unicode.html][2]  or [http://unicode.org/charts/charindex.html][3] . Just try scrolling down and see the variations of letters. 

How can I convert all these with Java? Please help me :(

  [1]: http://www.ssec.wisc.edu/~tomw/java/unicode.html
  [2]: http://www.ssec.wisc.edu/~tomw/java/unicode.html
  [3]: http://unicode.org/charts/charindex.html

Converting Symbols, Accent Letters to English Alphabet

In java, what does the private static method `registerNatives()` of the Object class do?

What does the registerNatives() method do?

Is it possible to add a file (not necessarily a jar file) to java classpath at runtime.
Specifically, the file already is present in the classpath, what I want is whether I can add a modified copy of this file to the classpath.

Thanks,

Adding files to java classpath at runtime

We&#39;re starting to make heavier use of GWT in our projects, and the performance of the GWT compiler is becoming increasingly annoying. 

We&#39;re going to start altering our working practices to mitigate the problem, including a greater emphasis on the hosted-mode browser, which defers the need to run the GWT compiler until a later time, but that brings its own risks, particularly that of not catching issues with real browsers until much later than we&#39;d like.

Ideally, we&#39;d like to make the GWT compiler itself quicker - a minute to compile a fairly small application is taking the piss. However, we are using the compile if a fairly naive fashion, so I&#39;m hoping we can make some quick and easy gains.

We&#39;re currently invoking com.google.gwt.dev.Compiler as a java application from ant Ant target, with 256m max heap and lots of stack space. The compiler is launched by Ant using fork=true and the latest Java 6 JRE, to try and take advantage of Java6&#39;s improved performance. We pass our main controller class to the compiler along with the application classpath, and off it goes.

What else can we do to get some extra speed? Can we give it more information so it spends less time doing discovery of what to do?

I know we can tell it to only compile for one browser, but we need to do multi-browser testing, so that&#39;s not really practical.

All suggestions welcome at this point.

How do I speed up the gwt compiler?

Should you place the `@Transactional` in the `DAO` classes and/or their methods or is it better to annotate the Service classes which are calling using the DAO objects? Or does it make sense to annotate both &quot;layers&quot;?

Where does the @Transactional annotation belong?

Why am I getting an error &quot;Attribute value must be constant&quot;. Isn&#39;t **null** constant???

    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface SomeInterface {
        Class&lt;? extends Foo&gt; bar() default null;// this doesn&#39;t compile
    }

Error setting a default null value for an annotation&#39;s field

I am having trouble setting the type of a String, it goes like

	public void setTextDesc(String textDesc) {
		this.textDesc = textDesc;
	}

	@Column(name=&quot;DESC&quot;)
	@Lob
	public String getTextDesc() {
		return textDesc;
	}

and it didn&#39;t work, I checked the mysql schema and it remains varchar(255), I also tried, 

	@Column(name=&quot;DESC&quot;, length=&quot;9000&quot;)
	
or

	@Column(name=&quot;DESC&quot;)
	@Type(type=&quot;text&quot;)
	
I am trying to make the type to be TEXT, any idea would be well appreciated!

Text Field using Hibernate Annotation

I defined my own custom annotation

    @Target(value={ElementType.METHOD, ElementType.FIELD})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface MyCustomAnnotation  {
	    Class&lt;?&gt; myType();
    }

how, if at all, can I make the attribute optional


java custom annotation: make an attribute optional

What are the major areas that we can use Annotations? Is the feature a replacement for XML based configuration?

How and where are Annotations used in Java?

Overriding &quot;+=&quot; in Python? (__iadd__() method)

Is there way to override return types in C#? If so how, and if not why and what is a recommended way of doing it?

My case is that I have an interface with an abstract base class and descendants of that. I would like to do this (ok not really, but as an example!) :

    public interface Animal
    {
       Poo Excrement { get; }
    }

    public class AnimalBase
    {
       public virtual Poo Excrement { get { return new Poo(); } }
    }

    public class Dog
    {
      // No override, just return normal poo like normal animal
    }

    public class Cat
    {
      public override RadioactivePoo Excrement { get { return new RadioActivePoo(); } }
    }

`RadioactivePoo` of course inherits from `Poo`.

My reason for wanting this is so that those who use `Cat` objects could use the `Excrement` property without having to cast the `Poo` into `RadioactivePoo` while for example the `Cat` could still be part of an `Animal` list where users may not necessarily be aware or care about their radioactive poo. Hope that made sense...

As far as I can see the compiler doesn&#39;t allow this at least. So I guess it is impossible. But what would you recommend as a solution to this? 

C#: Overriding return types

In Java, for example, the `@Override` annotation not only provides compile-time checking of an override but makes for excellent self-documenting code. 

I&#39;m just looking for documentation (although if it&#39;s an indicator to some checker like pylint, that&#39;s a bonus). I can add a comment or docstring somewhere, but what is the idiomatic way to indicate an override in Python?

In Python, how do I indicate I&#39;m overriding a method?

Consider the following code:

    class Base(object):
    
        @classmethod
        def do(cls, a):
            print cls, a
    
    class Derived(Base):
    
        @classmethod
        def do(cls, a):
            print &#39;In derived!&#39;
            # Base.do(cls, a) -- can&#39;t pass `cls`
            Base.do(a)
    
    if __name__ == &#39;__main__&#39;:
        d = Derived()
        d.do(&#39;hello&#39;)

    &gt; $ python play.py  
    &gt; In derived! 
    &gt; &lt;class &#39;__main__.Base&#39;&gt; msg

From `Derived.do`, how do I call `Base.do`? 

I would normally use `super` or even the base class name directly if this is a normal object method, but apparently I can&#39;t find a way to call the classmethod in the base class. 

In the above example, `Base.do(a)` prints `Base` class instead of `Derived` class.


Calling a base class&#39;s classmethod in Python

Wondering what the difference is between the following:

Case 1: Base Class

    public void DoIt();

Case 1: Inherited class 

    public new void DoIt();

Case 2: Base Class

    public virtual void DoIt();

Case 2: Inherited class 

    public override void DoIt();

Both case 1 and 2 appear to have the same effect based on the tests I have run. Is there a difference, or a preferred way?

Difference between new and override

I am interating through classes in a Jar file and wish to find those which are not abstract. I can solve this by instantiating the classes and trapping InstantiationException but that has a performance hit as some classes have heavy startup. I can&#39;t find anything obviously like isAbstract() in the Class.java docs.


How can I determine whether a Java class is abstract by reflection

Why can&#39;t Java classes have abstract fields like they can with abstract methods?

For example: I have two classes that extend the same abstract base class.  These two classes each have a method that is identical except for a String constant, which happens to be an error message, within them. If fields could be abstract, I could make this constant abstract and pull the method up into the base class. Instead, I have to create an abstract method, called `getErrMsg()` in this case, that returns the String, override this method in the two derived classes, and then I can pull up the method (which now calls the abstract method).

Why couldn&#39;t I just make the field abstract to begin with? Could Java have been designed to allow this?

Why not abstract fields?

I am coming from c# where this was easy, and possible.

I have this code:

    public abstract class clsAbstractTable {
    	
    	public abstract String TAG;
        public abstract void init();
    
    }

but Eclipse tells me I use illegal modifier. 

I have this class:

    public class clsContactGroups extends clsAbstractTable {
    
    	
    }

I want the variable and method defined in such way, that Eclipse to **prompt me**, I have unimplemented abstract **variables** and methods.

How do I need to define my abstract class so I should be prompted to implement the abstracts?

**EDIT 1**

I will create different classes for different db tables. Each class should have it&#39;s own TABLENAME variable, no exception. I have to make sure this variable is static each time when I create a new class that extends the abstract class.

Then in the abstract class I will have a method eg: init();

If in this init() method I call TABLENAME, it should take the value from the sub-class.

something like this should also work out

    String tablename=(clsAbstract)objItem.TABLENAME;
    // where objItem can be any class that extended clsAbstract;

**EDIT 2**

I want a constant(static) defined in each class having it&#39;s name defined in abstract. 

 - I define variable TABLENAME in abstract, but no value given.
 - I create a clsContactGroups, I should be prompted to implement TABLENAME, this is where gets some data. eg: TABLENAME=&quot;contactgroups&quot;;
 - I create a second class clsContacts, I should be prompted to implement TABLENAME, this is where gets some data. eg: TABLENAME=&quot;contacts&quot;;  
etc...

Abstract variables in Java?

I&#39;ve set up an abstract parent class, and a concrete class which extends it. Why can the parent class not call the abstract function?

    //foo.php
    &lt;?php
        abstract class AbstractFoo{
            abstract public static function foo();
            public static function getFoo(){
                return self::foo();//line 5
            }
        }
        
        class ConcreteFoo extends AbstractFoo{
            public static function foo(){
                return &quot;bar&quot;;
            }
        }
        
        echo ConcreteFoo::getFoo();
    ?&gt;

Error: 

&gt; Fatal error: Cannot call abstract method AbstractFoo::foo() in **foo.php**  on line 5

Why can&#39;t you call abstract functions from abstract classes in PHP?

What is the difference between `sealed abstract` and `abstract` Scala class?

Content Type	Original Author	Original Content on Stackoverflow
Question	Eyvind	View Question on Stackoverflow
Solution 1 - Java	Andrzej Doyle	View Answer on Stackoverflow
Solution 2 - Java	Jon Skeet	View Answer on Stackoverflow
Solution 3 - Java	mR_fr0g	View Answer on Stackoverflow
Solution 4 - Java	Mark	View Answer on Stackoverflow

Should I add an @Override annotation when implementing abstract methods in Java?

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Solution 4 - Java

How can I see if a Perl hash already has a certain key?

What makes Ruby slow?

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