A very **very** good document regarding this topic is [Troubleshooting Guide for Java][1] from (originally) Sun. See the chapter &quot;Troubleshooting System Crashes&quot; for information about `hs_err_pid*` Files.

See [Appendix C - Fatal Error Log][2]

Per the guide, by default the file will be created in the working directory of the process if possible, or in the system temporary directory otherwise. A specific location can be chosen by passing in the `-XX:ErrorFile` product flag.  It says:

&gt; If the -XX:ErrorFile= file flag is not specified, the system attempts to create the file in the working directory of the process. In the event that the file cannot be created in the working directory (insufficient space, permission problem, or other issue), the file is created in the temporary directory for the operating system.

  [1]: https://web.archive.org/web/20210915102559/https://www.oracle.com/java/technologies/javase/6hotspotvm.html
  [2]: https://web.archive.org/web/20201025232140/https://www.oracle.com/java/technologies/javase/felog.html#gbwcy

    int a = 10;
    switch(a){
    case 0:
        printf(&quot;case 0&quot;);
        break;
    case 1:
        printf(&quot;case 1&quot;);
        break;
    }

Is the above code valid?

If I am sure that int `a` will not have any other value than 1 and 0, can I avoid `default`?

What if in any case a value will be different from 1 and 0?

I know this is a silly question but I was thinking that perhaps it would be illegal or undefined behavior soI just asked to make sure.

What if I don&#39;t write default in switch case?

What for do we need ARM EABI v7a System image in Android development?
What is the purpose of that particular image?

What is the use of ARM EABI v7a System image in android?

Are any specific settings required on the Java tab of Tomcat configuration tool in order to generate a `hs_err_pid.log` file?

What is the default location of the `hs_err_pid.log` file? Can this location be changed?

What are hs_err_pid.log files generated when Tomcat crashes?

<p>Are any specific settings required on the Java tab of Tomcat configuration tool in order to generate a <code>hs_err_pid.log</code> file?</p>
<p>What is the default location of the <code>hs_err_pid.log</code> file? Can this location be changed?</p>


I&#39;ve searched for this, but couldn&#39;t find an answer and for whatever reason I was too ashamed to ask professor, due to that feeling when hundreds of people stare at you... 

Anyhow, my question is what&#39;s the importance of having brackets? Is it OK if I omit them? Example:

    for (int i = 0; i &lt; size; i++)  {
       a += b;
    }

vs

    for (int i = 0; i &lt; size; i++)
       a += b;

I know both of them will work, but if I omit the brackets (which I tend to do a lot, due to visibility) will that change anything, anything at all? As I said, I know it works, I tested it dozen of times, but now some of my uni assignments are getting larger, and for some reason I have irrational fear that in the long run, this my cause some problems? Is there a reason to fear that?

Is it ok if I omit curly braces in Java?

What is the simplest way to get a list of all items within an S3 bucket using Java?

    List&lt;S3ObjectSummary&gt; s3objects = s3.listObjects(bucketName,prefix).getObjectSummaries();

This example only returns 1000 items.

How to list all AWS S3 objects in a bucket using Java

I try to convert an integer to an array. For example, 1234 to `int[] arr = {1,2,3,4};`.

I&#39;ve written a function:

    public static void convertInt2Array(int guess)  {
        String temp = Integer.toString(guess);
        String temp2;
        int temp3;
        int [] newGuess = new int[temp.length()];
        for(int i=0; i&lt;=temp.length(); i++) {
            if (i!=temp.length()) {
                temp2 = temp.substring(i, i+1);
            } else {
                temp2 = temp.substring(i);
                //System.out.println(i);
            }
            temp3 =  Integer.parseInt(temp2);
            newGuess[i] = temp3;
        }

        for(int i=0; i&lt;=newGuess.length; i++) {
            System.out.println(newGuess[i]);
        }
    }

But an exception is thrown:

&gt;    Exception in thread &quot;main&quot; java.lang.NumberFormatException: For input string: &quot;&quot; &lt;br/&gt;
        at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) &lt;br/&gt;
 &lt;br/&gt;
        at java.lang.Integer.parseInt(Integer.java:504) &lt;br/&gt;
        at java.lang.Integer.parseInt(Integer.java:527) &lt;br/&gt;
        at q4.test.convertInt2Array(test.java:28) &lt;br/&gt;
        at q4.test.main(test.java:14) &lt;br/&gt;
    Java Result: 1 &lt;br/&gt;

How can I fix this?


Convert an integer to an array of digits

I&#39;ve got a collection of Duck objects and I&#39;d like to **sort them using multiple keys**.

    class Duck {
        DuckAge age; //implements Comparable
        DuckWeight weight; //implements Comparable
        String name;
    }
    List&lt;Duck&gt; ducks = Pond.getDucks();

eg. I want to sort them **primarily by their weights**, and **secondarily by their age**. If two ducks have the exact same weight and the exact same age, then let&#39;s differentiate them using their **names as a tertiary key**. I might do something like this:

    Collections.sort(ducks, new Comparator&lt;Duck&gt;(){
        @Override
        public int compare(Duck d1, Duck d2){
            int weightCmp = d1.weight.compareTo(d2.weight);
            if (weightCmp != 0) {
                return weightCmp;
            }
            int ageCmp = d1.age.compareTo(d2.age);
            if (ageCmp != 0) {
                return ageCmp;
            }
            return d1.name.compareTo(d2.name);
        }
    });

Well I do this quite frequently, but this solution doesn&#39;t smell right. It doesn&#39;t scale well, and it&#39;s easy to mess up. Surely there must be a better way of sorting Ducks using multiple keys! Does anybody know of a better solution?

**EDIT** removed unnecessary `else` branches

Sorting Java objects using multiple keys

Will google Go use less resources than Python and Java on Appengine? Are the instance startup times for go faster than Java&#39;s and Python&#39;s startup times? 

Is the go program uploaded as binaries or source code and if it is uploaded as source code is it then compiled once or at each instance startup?

In other words: Will I benefit from using Go in app engine from a cost perspective? (only taking to account the cost of the appengine resources not development time)

Resource usage of google Go vs Python and Java on Appengine

I just downloaded the Tomcat 7.0.23 package on my Ubuntu 11.10. 

I followed the instructions on a Google API website to [deploy their example webapp][1]. It basically consists of ``jar`` files placed in the ``WEB-INF/lib`` directory and a ``web.xml`` file placed in the ``WEB-INF`` directory. 

Yet the app is not automatically deployed and when trying to *force* the server to deploy it through the manager gui, I get the following message:

    FAIL - Application at context path /myWebApp could not be started
    FAIL - Encountered exception org.apache.catalina.LifecycleException: 
             Failed to start component 
             [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/myWebApp]]


  [1]: http://code.google.com/apis/chart/interactive/docs/dev/dsl_get_started.html#webapp


However, the JSP examples provided with Tomcat do work!

I have the same problem on Tomcat6.

So what did I do wrong ? Is this a permission problem ? (I even try to change the mod of all files to 777).

Tomcat: LifecycleException when deploying

I integrated Tomcat 7 in Eclipse. When I start it using Eclipse, it shows that Tomcat is up and running, but when I go to http://localhost:8080 in my browser, it gives me following error:

&gt; ##HTTP Status 404 - /

&gt; **type** Status report

&gt; **message** /

&gt; **description** The requested resource (/) is not available.  

&gt; Apache Tomcat/7.0.23

I tried changing the port in `server.xml` just in case if 8080 is used by another service, but it didn&#39;t work either. How can I solve it?

HTTP Status 404 - The requested resource (/) is not available

I am using Tomcat 7 in Eclipse on Windows. When starting Tomcat, I am getting the following info message:

&gt; The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path

What does this mean and how can I provide the APR library?

What does &quot;The APR based Apache Tomcat Native library was not found&quot; mean?

Currently I have 2 web applications app1 and app2 running on Tomcat 6:

- app1 on http://localhost:8080/app1 
- app2 on http://localhost:8080/app2

I want to configure Tomcat so that they run in root context behind separate ports:

- app1 on http://localhost:8081
- app2 on http://localhost:8082

What needs to be done?



How to run different apps on single Tomcat instance behind different ports?

It is said that in the Spring javadoc article about `DriverManagerDataSource` class, that this class is very simple and that it is recommended

&gt;to use a JNDI DataSource provided by the container. Such a `DataSource` can be exposed as a `DataSource` bean in a Spring ApplicationContext via `JndiObjectFactoryBean`

The question is: **how do I accomplish this?**

For example, if I wish to have `DataSource` bean to access my custom MySQL database, what would I require then? What should I write in the context configuration, etc?

How to use JNDI DataSource provided by Tomcat in Spring?

Recently we came across a situation where we wanted to see the debug info from the app which a user has on his device. So, what I am looking for is a way to find the log on the device, paste it as inline text on a mail and allow the user to send it..

Any ideas? Here are the questions again..
1)Find a debug log on the device
2)open the file and attach the contents of the file as inline text in to the mail.
3)Allow the user to email it the next time app launches..

Thanks,

iOS crash log catch, debug info.. Catch and send via email to the Dev team

I&#39;m trying to make a Python program that interfaces with a different crashy process (that&#39;s out of my hands). Unfortunately the program I&#39;m interfacing with doesn&#39;t even crash reliably! So I want to make a quick C++ program that crashes on purpose but I don&#39;t actually know the best and shortest way to do that, does anyone know what to put between my:

    int main() {
        crashyCodeGoesHere();
    }


to make my C++ program crash reliably

What is the easiest way to make a C++ program crash?

Hopefully this will be a quick fix.  I have been trying to figure out the error that i keep getting.  The error is listed below and the appdelagate is below that.

Any help is appreciated.

Thanks

&gt; 2012-04-12 21:11:52.669 Chanda[75100:f803] --- Assertion failure in `-[UITableView _endCellAnimationsWithContext:]`, `/SourceCache/UIKit_Sim/UIKit-1914.84/UITableView.m:1037`
&gt; 2012-04-12 21:11:52.671 Chanda[75100:f803] --- Terminating app due to uncaught exception &#39;`NSInternalInconsistencyException`&#39;, reason: &#39;Invalid update: invalid number of rows in section 0.  The number of rows contained in an existing section after the update (2) must be equal to the number of rows contained in that section before the update (2), plus or minus the number of rows inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).&#39;

    #import &quot;AppDelegate.h&quot;
    
    @implementation AppDelegate
    
    @synthesize window = _window;
    @synthesize databaseName,databasePath; 
    
    - (BOOL)application: (UIApplication *)application didFinishLaunchingWithOptions: (NSDictionary *)launchOptions {
        self.databaseName = @&quot;Customers.db&quot;;
        
        NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentDir = [documentPaths objectAtIndex:0];
        self.databasePath = [documentDir stringByAppendingPathComponent:self.databaseName];
        [self createAndCheckDatabase];
        
        return YES;
    }
    
    - (void)createAndCheckDatabase {
        BOOL success;
        
        NSFileManager *fileManager = [NSFileManager defaultManager];
        success = [fileManager fileExistsAtPath:databasePath];
        
        if (success) return; 
        
        NSString *databasePathFromApp = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:self.databaseName];
        
        [fileManager copyItemAtPath:databasePathFromApp toPath:databasePath error:nil];
    }
    
    @end

Assertion failure in -[UITableView _endCellAnimationsWithContext:]

In the app I&#39;m developing on Android, I keep getting a Fatal Signal 11 error.

I think it&#39;s something to do with the way that I&#39;m accessing the memory but I can&#39;t figure out what is causing it. 

Any help will be much appreciated!

Here&#39;s the LogCat:

    05-02 23:47:17.618: D/dalvikvm(590): GC_FOR_ALLOC freed 68K, 4% free 6531K/6787K, paused 101ms
    05-02 23:47:17.638: I/dalvikvm-heap(590): Grow heap (frag case) to 7.619MB for 1228816-byte allocation
    05-02 23:47:17.738: D/dalvikvm(590): GC_CONCURRENT freed 1K, 4% free 7730K/8007K, paused 5ms+14ms
    05-02 23:47:17.878: D/dalvikvm(590): GC_FOR_ALLOC freed &lt;1K, 4% free 7730K/8007K, paused 37ms
    05-02 23:47:17.888: I/dalvikvm-heap(590): Grow heap (frag case) to 8.790MB for 1228816-byte allocation
    05-02 23:47:17.998: D/dalvikvm(590): GC_CONCURRENT freed &lt;1K, 4% free 8930K/9223K, paused 4ms+4ms
    05-02 23:47:17.998: A/libc(590): Fatal signal 11 (SIGSEGV) at 0x00000000 (code=1)



Android Fatal Signal 11

Ok, here is the deal, I **hate** putting out questions about my debugging and crashes. Because I usually handle them myself, but I just **cannot** get my way around this, even after **viewing multiple questions already**.

Ok so here is the problem, I find my app randomly on and off crashing with this stack trace:


    *** -[ViewController respondsToSelector:]: message sent to deallocated instance 0x1e5d2ef0

Where `ViewController` can vary, sometimes the place where my code crashes, has **NO** relevance to that particular `ViewController` and doesn&#39;t own or call it.

Also, to get that console trace, I have enabled Zombies, otherwise I would get no console print at all, I would only get: `objc_msgSend`, which I know means I am messaging something that is released. But I cannot find where that is... I am really stuck! Usually I **always** debug my crashes, so I am really stuck on this.

Again, this crashes in different places at different times, on and off. And the place it crashes has almost **no** relevance to the `ViewController`. And I find this very confusing. 

Do you need any of my code? I have **a lot** of files and since it is crashing in different places, distributing my code will be a mess!

I have tried to add symbolic breakpoints with no luck, and Zombies is not available on the Instruments application for iOS. I cannot run my app on the simulator as it has unsupportive architecture frameworks for it.

Thanks everyone...

ViewController respondsToSelector: message sent to deallocated instance (CRASH)

What are the default values for the following options in Java 6 on a *non-server-class machine*?

 - -Xmx
 - -XX:MaxPermSize

Oracle&#39;s [documentation][1] states that:

&gt; On server-class machines running the server VM, the garbage collector (GC) has changed from the previous serial collector (-XX:+UseSerialGC) to a parallel collector (-XX:+UseParallelGC).

and

&gt; On server-class machines running either VM (client or server) with the parallel garbage collector (-XX:+UseParallelGC) the initial heap size and maximum heap size have changed

The page doesn&#39;t describe the defaults for non-server-class machines, only that, for example, the initial heap size is &quot;a reasonable minimum&quot;. Looking at [the &#39;man page&#39;][2] for the `java` command there is the following against `-Xms`:

&gt; The default value is chosen at runtime based on system configuration 


  [1]: http://docs.oracle.com/javase/6/docs/technotes/guides/vm/gc-ergonomics.html
  [2]: http://docs.oracle.com/javase/6/docs/technotes/tools/windows/java.html

Default values for Xmx, Xms, MaxPermSize on non-server-class machines

We&#39;ve run into a **Java.lang.OutOfMemoryError: PermGen space** error and looking at the tomcat JVM params, other than the `-Xms` and `-Xmx` params we also specify `-XX:MaxPermSize=128m`. After a bit of profiling I can see occasionally garbage collection happening on the PermGen space saving it from running full.

My question is: other than increasing the `-XX:MaxPermSize` what would be the difference if I specify as well `-XX:PermSize`? I know the total memory then would be **Xmx+maxPermSize** but is there any other reason why `-XX:PermSize` should **not** be there when `-XX:MaxPermSize` is specified?

Please do share if you have real-world experience dealing with these JVM parameters.

ps. The JVM is HotSpot 64bit Server VM build 16.2-b04



-XX:MaxPermSize with or without -XX:PermSize

For example:
    
    class A {
        static int i=0;
        static int j;

       static void method() {
           // static k=0; can&#39;t use static for local variables only final is permitted
           // static int L;
        }
    }

Where will these variables be stored in Java, in heap or in stack memory? How are they stored?

Where are static methods and static variables stored in Java?

I am unable to understand the following text... Does it mean that `&lt;clinit&gt;` is for empty constructors? Why is important to have two different versions?

https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-2.html

&gt;     2.9. Special Methods
&gt; 
&gt; At the level of the Java virtual machine, every constructor (&#167;2.12) appears as an instance initialization method that has the
&gt; special name `&lt;init&gt;`. This name is supplied by a compiler. Because the
&gt; name `&lt;init&gt;` is not a valid identifier, it cannot be used directly in a
&gt; program written in the Java programming language. Instance
&gt; initialization methods may be invoked only within the Java virtual
&gt; machine by the invokespecial instruction, and they may be invoked only
&gt; on uninitialized class instances. An instance initialization method
&gt; takes on the access permissions (&#167;2.7.4) of the constructor from which
&gt; it was derived.
&gt;     
&gt; A class or interface has at most one class or interface initialization method and is initialized (&#167;2.17.4) by invoking that
&gt; method. The initialization method of a class or interface is static
&gt; and takes no arguments. It has the special name `&lt;clinit&gt;`. This name is
&gt; supplied by a compiler. Because the name `&lt;clinit&gt;` is not a valid
&gt; identifier, it cannot be used directly in a program written in the
&gt; Java programming language. Class and interface initialization methods
&gt; are invoked implicitly by the Java virtual machine; they are never
&gt; invoked directly from any Java virtual machine inw2struction, but are
&gt; invoked only indirectly as part of the class initialization process.

Java: What is the difference between &lt;init&gt; and &lt;clinit&gt;?

I am studying new features of JDK 1.7 and I just can&#39;t get it what MethodHandle is designed for? I understand (direct) invocation of the static method (and use of Core Reflection API that is straightforward in this case). I understand also (direct) invocation of the virtual method (non-static, non-final) (and use of Core Reflection API that requires going through Class&#39;s hierarchy `obj.getClass().getSuperclass()`). Invocation of non-virtual method can be treated as special case of the former one.

Yes, I aware that there is an issue with overloading. If you want to invoke method you have to supply the exact signature. You can&#39;t check for overloaded method in easy way.

But, what is MethodHandle about? Reflection API allows you to &quot;look on&quot; the object internals without any pre-assumption (like implemented the interface). You can inspect the object for some purpose. But what is MethodHandle is designed too? Why and when should I use it?

**UPDATE:** I am reading now this http://blog.headius.com/2008/09/first-taste-of-invokedynamic.html article. According to it, the main goal is to simplify life for scripting languages that runs atop of JVM, and not for Java Language itself.

**UPDATE-2:** I finish to read the link above, some quotation from there:

&gt;The JVM is going to be the best VM for building dynamic languages, because it already is a dynamic language VM. And InvokeDynamic, by promoting dynamic languages to first-class JVM citizens, will prove it.
&gt;
&gt;Using reflection to invoke methods works great...except for a few problems. Method objects must be retrieved from a specific type, and can&#39;t be created in a general way.&lt;...&gt; 
&gt;
&gt;...reflected invocation is a lot slower than direct invocation. Over the years, the JVM has gotten really good at making reflected invocation fast. Modern JVMs actually generate a bunch of code behind the scenes to avoid a much of the overhead old JVMs dealt with. But the simple truth is that reflected access through any number of layers will always be slower than a direct call, partially because the completely generified &quot;invoke&quot; method must check and re-check receiver type, argument types, visibility, and other details, but also because arguments must all be objects (so primitives get object-boxed) and must be provided as an array to cover all possible arities (so arguments get array-boxed).
&gt;
&gt;The performance difference may not matter for a library doing a few reflected calls, especially if those calls are mostly to dynamically set up a static structure in memory against which it can make normal calls. But in a dynamic language, where every call must use these mechanisms, it&#39;s a severe performance hit.

http://blog.headius.com/2008/09/first-taste-of-invokedynamic.html

So, for Java programmer it is essentially useless. Am I right? From this point of view, It can be only considered as alternative way for Core Reflection API.

**UPDATE-2020:** Indeed, MethodHandle can be thought as s more powerful alternative to Core Reflection API. Starting with JDK 8 there are also Java Language features that use it.

Content Type	Original Author	Original Content on Stackoverflow
Question	user1030969	View Question on Stackoverflow
Solution 1 - Java	Eduard Wirch	View Answer on Stackoverflow

What are hs_err_pid.log files generated when Tomcat crashes?

Java Problem Overview

Java Solutions

Solution 1 - Java

What is the use of ARM EABI v7a System image in android?

What if I don't write default in switch case?

Attributions