Yes.

If a mapping to the specified key already exists, the old value will be replaced (and returned). See [`Hashtable.put()`][1].

For multi-threaded environment, I&#39;d recommend [`ConcurrentHashMap`][2] or another `ConcurrentMap` implementation. Though `Hashtable` is synchronized, there are more sophisticated implementations available now for concurrent mapping, such as Guava&#39;s [`MapMaker`][3] and [`CacheBuilder`][4].

Also keep in mind the `Map` is going to have the type parameters `&lt;Integer, String&gt;` since primitive type parameters aren&#39;t supported.


  [1]: http://docs.oracle.com/javase/8/docs/api/java/util/Hashtable.html#put-K-V-
  [2]: http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentHashMap.html
  [3]: https://google.github.io/guava/releases/snapshot/api/docs/com/google/common/collect/MapMaker.html
  [4]: https://google.github.io/guava/releases/snapshot/api/docs/com/google/common/cache/CacheBuilder.html

hmmm ,just need add a line  
`myHashtable.put(1,&quot;fish&quot;); `  
to see what&#39;s amazing happens

see this links:[http://docs.oracle.com/javase/6/docs/api/java/util/Hashtable.html#put(K, V)][1]

    Returns:
    the previous value of the specified key in this hashtable, or null if it did not have one


  [1]: http://docs.oracle.com/javase/6/docs/api/java/util/Hashtable.html#put%28K,%20V%29

I have this very annoying problem that in Razor Views the Enter, Backspace and the navigation keys frequently do not respond. I have to restart VS to get it back to normal again. Am I missing something?

Enter., Backspace and the navigation keys not responding in Visual Studio 2010 w/ Powertools/Resharper

In many places in the web, you will see:
 
&gt; What is the memory limit on a node process?

and the answer:

&gt; Currently, by default V8 has a memory limit of 512mb on 32-bit systems, and 1gb on 64-bit systems. The limit can be raised by setting --max-old-space-size to a maximum of ~1gb (32-bit) and ~1.7gb (64-bit), but it is recommended that you split your single process into several workers if you are hitting memory limits.

**Can somebody confirm this is the case as Node.js seems to update frequently?**

**And more importantly, will it be the case in the near future?** 

I want to write JavaScript code which might have to deal with 4gb of javascript objects (and speed might not be an issue).

If I can&#39;t do it in Node, I will end up doing in java (on a 64bit machine) but I would rather not.



memory limit in Node.js (and chrome V8)

New to hashtables with a simple question.  For some reason googling hasn&#39;t gotten me a straight answer.  Say I&#39;ve got an `&lt;int,String&gt;` hashtable set up:

    myHashtable.put(1,&quot;bird&quot;);
    myHashtable.put(2,&quot;iguana&quot;);

and I want to change &quot;bird&quot; to &quot;fish&quot; (and leave the index the same).  Can I just do a simple `put`, or do I need to delete the entry, or what?  


Does &quot;put&quot; overwrite existing values?

New to hashtables with a simple question. For some reason googling hasn't gotten me a straight answer. Say I've got an <code>&#x3C;int,String></code> hashtable set up:
<pre><code class="hljs language-arduino">myHashtable.put(1,"bird");
myHashtable.put(2,"iguana");
</code></pre>
and I want to change "bird" to "fish" (and leave the index the same). Can I just do a simple <code>put</code>, or do I need to delete the entry, or what?

I read many articles to understand Java servlet but I did not succeed.

Can you please give brief introduction of Java servlets (in easy language). What is a servlet? What are the advantages?

I can&#39;t understand the difference between server-side programming languages (PHP, ASP) and servlets.

What is Java Servlet?

How do you access the values in the &lt;code&gt;res/values/string.xml&lt;/code&gt; resource file from the Android &lt;code&gt;Activity class&lt;/code&gt;?

Access string.xml Resource File from Java Android Code

I&#39;ve recently started learning and exploring the basics of GUI programming in Java.

Having been programming for a while I have only done backend work or work and as a result the closest I&#39;ve gotten to user interfaces is the command console (embarrassing I know).

I&#39;m using Swing and as far as I can gather that means by extension I am also using AWT.


My question is based on this piece of code:

    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new frame.setVisible(true);
        }
    } );


I have been researching this for a while as I wanted to fully understand this strange piece of code and have come across the term &#39;Event-Dispatching Thread&#39; multiple times. Correct me if I&#39;m wrong but as I understand it; it has to do with using multiple threads and how Java Swing interprets those threads. I gather as well that the above code is used to make sure all the threads are &#39;safe&#39; before it creates the window, hence the invokeLater?

I have read that:

&gt; &quot;You can only call methods that operate on the frame from the Event-Dispatching Thread&quot;

and that only under certain circumstances can you call methods that operate on the frame from the main method. 

**Can somebody please clarify to me what exactly the Event-Dispatching Thread is?**

**How it relates to multiple threads of execution and how those threads are not safe to be called from the main method? Also why do we need this invokeLater?**

**Can we not just create the window as any other object?**

I&#39;ve hit a bit of a road block in my research as I&#39;m not grasping these relations and ideas.

A side note is that I like to base my knowledge on in-depth understanding as I believe this leads to the best overall outcome and as a result the best programs. If I understand in-depth how something works then you can use the tips and tweaks effectively rather than just parroting them back in to code, so please don&#39;t be afraid to give me some extra in-depth explanations and broaden my knowledge.

Thank you.

Java Event-Dispatching Thread explanation

Why is `08` considered an out of range int but `07` and below are not?

Why is 08 not a valid integer literal in Java?

This is a basic question but I can&#39;t find an answer.  I&#39;ve looked into floating point arithmetic and a few other topics but nothing has seemed to address this.  I&#39;m sure I just have the wrong terminology.

Basically, I want to take two quantities - completed, and total - and divide them to come up with a percentage (of how much has been completed).  The quantities are `long`s.  Here&#39;s the setup:

    long completed = 25000;
    long total = 50000;

    System.out.println(completed/total);  // Prints 0

I&#39;ve tried reassigning the result to a double - it prints `0.0`.  Where am I going wrong?

Incidentally, the next step is to multiply this result by 100, which I assume should be easy once this small hurdle is stepped over.

BTW not homework here just plain old numskull-ness (and maybe too much coding today).

Division of integers in Java

I&#39;m using a ResultSet in Java, and am not sure how to properly close it. I&#39;m considering using the ResultSet to construct a HashMap and then closing the ResultSet after that. Is this HashMap technique efficient, or are there more efficient ways of handling this situation? I need both keys and values, so using a HashMap seemed like a logical choice.

If using a HashMap is the most efficient method, how do I construct and use the HashMap in my code?

Here&#39;s what I&#39;ve tried:

    public HashMap resultSetToHashMap(ResultSet rs) throws SQLException {
      
      ResultSetMetaData md = rs.getMetaData();
      int columns = md.getColumnCount();
      HashMap row = new HashMap();
      while (rs.next()) {
         for (int i = 1; i &lt;= columns; i++) {
           row.put(md.getColumnName(i), rs.getObject(i));
         }
      }
      return row;
    }

Efficient way to Handle ResultSet in Java

Is it possible to have a `HashMap` return a default value for all keys that are not found in the set?

HashMap to return default value for non-found keys?

How to send `HashMap` value from one Intent to second Intent? 

Also, how to retrieve that `HashMap` value in the second Activity?


How to send hashmap value to another activity using an intent

Is it appropriate to use integers as keys in a Ruby hash?

Every example from documentation shows a string or symbol being used as a key, but never an integer.

Internally, would integers somehow get converted to strings? I have seen some conflicting information on the subject.

In other words, is there any significant disadvantage to using integer keys to a hash?


Usage of integers as hash keys

Is it bad practice to use mutable objects as Hashmap keys?  What happens when you try to retrieve a value from a Hashmap using a key that has been modified enough to change its hashcode?

For example, given

    class Key
    {
        int a; //mutable field
        int b; //mutable field
    
        public int hashcode()
            return foo(a, b);
        // setters setA and setB omitted for brevity
    }

with code

    HashMap&lt;Key, Value&gt; map = new HashMap&lt;Key, Value&gt;();

    Key key1 = new Key(0, 0);
    map.put(key1, value1); // value1 is an instance of Value

    key1.setA(5);
    key1.setB(10);

What happens if we now call `map.get(key1)`?  Is this safe or advisable?  Or is the behavior dependent on the language?

Are mutable hashmap keys a dangerous practice?

I&#39;m working on hash table in C language and I&#39;m testing hash function for string.

The first function I&#39;ve tried is to add ascii code and use modulo (`% 100`) but i&#39;ve got poor results with the first test of data: 40 collisions for 130 words. 

The final input data will contain 8000 words (it&#39;s a dictionary stores in a file). The hash table is declared as `int table[10000]` and contains the position of the word in a .txt file.

- Which is the best algorithm for hashing string? 
- And how to determinate the size of hash table?

hash function for string

I am writing program that does *alot* of table lookups. As such, I was perusing the Haskell documentation when I stumbled upon `Data.Map` (of course), but also `Data.HashMap` and `Data.Hashtable`. I am no expert on hashing algorithms and after inspecting the packages they all seem really similar. As such I was wondering:

1: what are the major differences, if any?

2: Which would be the most performant with a high volume of lookups on maps/tables of ~4000 key-value pairs?


Performant Haskell hashed structure.

As we know the purpose of &quot;final&quot; keyword in java. While declaring a variable as final, we have to initialize the variable. like &quot;**final int a=10;&quot;**
   We can not change the value of &quot;a&quot;. But if we go for HashTable its possible to add some value even declaring the HashTable as final.
 
Example::

     private static final Hashtable&lt;String,Integer&gt; MYHASH = new Hashtable&lt;String,Integer&gt;() 
    {{     put(&quot;foo&quot;,      1);     
           put(&quot;bar&quot;,      256);     
           put(&quot;data&quot;,     3);     
           put(&quot;moredata&quot;, 27);     
           put(&quot;hello&quot;,    32);     
           put(&quot;world&quot;,    65536);  }}; 


Now I am declaring the MYHASH HashTable as final. If I try to add some more elements to this, its accepting.

    MYHASH.put(&quot;NEW DATA&quot;,      256);

Now the &quot;NEW DATA&quot; is added to the HashTable.
My questions is Why its allowing to add even its declaring as final????







Creating Hashtable as final in java

As far as I know, [`java.util.Hashtable`][1] synchronizes each and every method in the [`java.util.Map`][2] interface, while [`Collections.synchronizedMap(hash_map)`][3] returns a wrapper object containing synchronized methods delegating calls to the actual `hash_map` (correct me if I am wrong).

**I have two questions :**

1. What difference does it make to synchronize each and every method and to have a wrapper class? What are the scenarios to choose one over the other?

2. What happens when we do `Collections.synchronizedMap(hash_table)`? Will this be equal to simply using a normal `java.util.Hashtable`?


  [1]: http://docs.oracle.com/javase/7/docs/api/java/util/Hashtable.html
  [2]: http://docs.oracle.com/javase/7/docs/api/java/util/Map.html
  [3]: http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html#synchronizedMap(java.util.Map)

Difference between Hashtable and Collections.synchronizedMap(HashMap)

I&#39;m using this (simplified) chunk of code to extract a set of tables from SQL Server with [BCP][1].

    $OutputDirectory = &quot;c:\junk\&quot;
    $ServerOption =   &quot;-SServerName&quot;
    $TargetDatabase = &quot;Content.dbo.&quot;

    $ExtractTables = @(
        &quot;Page&quot;
        , &quot;ChecklistItemCategory&quot;
        , &quot;ChecklistItem&quot;
    )

    for ($i=0; $i -le $ExtractTables.Length – 1; $i++)  {
        $InputFullTableName = &quot;$TargetDatabase$($ExtractTables[$i])&quot;
        $OutputFullFileName = &quot;$OutputDirectory$($ExtractTables[$i])&quot;
        bcp $InputFullTableName out $OutputFullFileName -T -c $ServerOption
    }

It works great, but now some of the tables need to be extracted via views, and some don&#39;t. So I need a data structure something like this:

    &quot;Page&quot;                      &quot;vExtractPage&quot;
    , &quot;ChecklistItemCategory&quot;   &quot;ChecklistItemCategory&quot;
    , &quot;ChecklistItem&quot;           &quot;vExtractChecklistItem&quot;

I was looking at hashes, but I&#39;m not finding anything on how to loop through a hash. What would be the right thing to do here? Perhaps just use an array, but with both values, separated by space?

Or am I missing something obvious?

  [1]: https://en.wikipedia.org/wiki/Bulk_Copy_Program


Content Type	Original Author	Original Content on Stackoverflow
Question	Ben	View Question on Stackoverflow
Solution 1 - Java	Paul Bellora	View Answer on Stackoverflow
Solution 2 - Java	JessonChan	View Answer on Stackoverflow

Does "put" overwrite existing values?

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

memory limit in Node.js (and chrome V8)

Enter., Backspace and the navigation keys not responding in Visual Studio 2010 w/ Powertools/Resharper

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