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ConcurrentHashMap vs Synchronized HashMap

What is the difference between using the wrapper class, SynchronizedMap, on a HashMap and ConcurrentHashMap? Is it just being able to modify the HashMap while iterating it (ConcurrentHashMap)?


Source: (StackOverflow)

Difference between core and processor?

What is the difference between a core and a processor?

I've already looked for it on Google, but I'm just having multi-core and multi-processor definition, but it doesn't match what I am looking for.


Source: (StackOverflow)

Treeset to order elements in descending order

Here is the piece of code that I have used for Java 5.0

TreeSet<Integer> treeSetObj = new TreeSet<Integer>( Collections.reverseOrder() ) ;

Collections.reverseOrder() is used to obtain a comparator in order to reverse the way the elements are stored and iterated.

Is there a more optimized way of doing it?


Source: (StackOverflow)

Strings are objects in Java, so why don't we use 'new' to create them?

We normally create objects using the new keyword, like:

Object obj = new Object();

Strings are objects, yet we do not use new to create them:

String str = "Hello World";

Why is this? Can I make a String with new?


Source: (StackOverflow)

What is SEGV_MAPERR?

What is SEGV_MAPERR, why does it always come up with SIGSEGV?


Source: (StackOverflow)

Confusing output from String.split

I do not understand the output of this code:

public class StringDemo{              
    public static void main(String args[]) {
        String blank = "";                    
        String comma = ",";                   
        System.out.println("Output1: "+blank.split(",").length);  
        System.out.println("Output2: "+comma.split(",").length);  
    }
}

And got the following output:

Output1: 1 
Output2: 0

Source: (StackOverflow)

How to analyze information from a Java core dump? [closed]

If a process crashes and leaves a core dump or I create one with gcore then how can I analyze it?

I'd like to be able to use jmap, jstack, jstat etc and also to see values of all variables.

This way I can find the reasons for a crashed or frozen JVM.


Source: (StackOverflow)

What is JAVA_HOME? How does the JVM find the javac path stored in JAVA_HOME?

I would like to know what is JAVA_HOME. Where do I set the path of javac.exe and java.exe. It is in environment variables. When I compile a Java program from command prompt, how does the JVM find javac.exe?


Source: (StackOverflow)

In python, is there a "pass" equivalent for a variable assignment

I am using a library function called get_count_and_price which returns a 2-tuple (count,price). In many places I use both time and price. However, in some I only need time or price. So right now, if I only need count, I assign to (count,price) and leave the price unused.

This works great and causes no trouble in and of itself.

However...

I use Eclipse with PyDev, and the new version 1.5 automatically shows errors and warnings. One of the warnings it shows is unused variables. In the above example, it flags price as unused. This is the sort of behavior which is great and I really appreciate PyDev doing this for me. However, I would like to skip the assignment to price altogether. Ideally, I would like something like:

(count,None) = get_count_and_price()

Now as we all know, None cannot be assigned to. Is there something else I could do in this case?

I know I could do something like

count = get_count_and_price()[0]

but I am asking just to see if anyone has any better suggestions.


Source: (StackOverflow)

How do I prepend a directory the library path when loading a core file in gdb on Linux

I have a core file generated on a remote system that I don't have direct access to. I also have local copies of the library files from the remote system, and the executable file for the crashing program.

I'd like to analyse this core dump in gdb.

For example:

gdb path/to/executable path/to/corefile

My libraries are in the current directory.

In the past I've seen debuggers implement this by supplying the option "-p ." or "-p /=."; so my question is:

How can I specify that libraries be loaded first from paths relative to my current directory when analysing a corefile in gdb?


Source: (StackOverflow)

One core exclusively for my process [duplicate]

Possible Duplicate:
how to set CPU affinity of a particular pthread?

Is there a way in Linux to disable one core for all processes except one process? I would like to have one core reserved only and only for my process.

Expected behavior is as follows:

  1. Processes which will be spawned after my process, should not see this core and use the others.
  2. When my process is spawned, all processes which are utilizing this core, should be switched to other cores.

Source: (StackOverflow)

How to integrate ZXing Library to Android Studio for Barcode Scanning?

I've been looking all over internet how to include zxing library to my project, and I found this tutorial: http://blog.dihaw.com/integrating-zxing-in-your-android-app-as-standalone-scanner/

But when I reach the point that you need to check for BeepManager to add the R import I get all kinds of errors in my project (Even on the MainActivity) that it couldn't find R.

Also I found this one https://github.com/journeyapps/zxing-android-embedded/blob/master/README.md which seemed a lot easier because it was auto integrated by gradle, but when I sync it pops an error that it couldn't find the files.

Any help would be appreciated :) I'm new to Android Studio.

EDIT:

I added the settings of the 2nd method (the one with the gradle settings) to my build.gradle and 4 error pop up:

Error:Failed to find: com.embarkmobile:zxing-android-legacy:2.0.0 
Error:Failed to find: com.google.zxing:core:3.0.1 
Error:Failed to find: com.embarkmobile:zxing-android-integration:2.0.0 
Error:Failed to find: com.embarkmobile:zxing-android-minimal:2.0.0

Any help?

---ANSWER---

To fix this problem I needed to disable Offline Work on Gradle. Go into Android Studio's settings>Gradle>Uncheck 'offline work' After that, you're good to go!


Source: (StackOverflow)

What is the use of static synchronized method in java? [duplicate]

This question already has an answer here:

I have one question in my mind , I read static synchronized method locked on class object and synchronized method locks on current instance of an object.So Whats the meaning of locked on class object ?

Can anyone please help me on this topic ?


Source: (StackOverflow)

How to access the private variables of a class in its subclass?

This is a question I was asked in an interview: I have class A with private members and Class B extends A. I know private members of a class cannot be accessed, but the question is: I need to access private members of class A from class B, rather than create variables with the same value in class B.


Source: (StackOverflow)

Is Math.max(a,b) or (a>b)?a:b faster in Java?

Which one is faster in Java and why?

  1. Math.max(a,b)
  2. (a>b)?a:b

(This was asked in an interview.)


Source: (StackOverflow)