You can use `_JAVA_OPTIONS` to pass *options to any* JVM process started on your system.

For example,

    set _JAVA_OPTIONS=-Dsun.java2d.noddraw=true

When a JVM starts, it parses the value of `_JAVA_OPTIONS` as if the parameters were at the command line of java. You can see the passed parameters via JVisualVM.

For more information, read the blog post: 
[What I discovered while trying to pass Default JVM Parameters][1]


  [1]: http://progexc.blogspot.co.il/2013/12/what-i-discovered-while-trying-to-pass.html


And according to https://bugs.openjdk.java.net/browse/JDK-4971166 undocumented Hotspot-specific `_JAVA_OPTIONS` was superseded by [`JAVA_TOOL_OPTIONS`][1] that is included in standard JVMTI specification, does better handling of quoted spaces and should be always preferred.

---

Since JDK 9+ there&#39;s also JDK_JAVA_OPTIONS as the preferred replacement, see https://stackoverflow.com/q/52986487/537554

  [1]: https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/envvars002.html

When you try to install some package of R from GitHub&#39;s repository

    install_github(&#39;rWBclimate&#39;, &#39;ropensci&#39;)

If you have the following error:
   
    Installing github repo(s) rWBclimate/master from ropensci
    Downloading rWBclimate.zip from https://github.com/ropensci/rWBclimate/archive/master.zip
    Error in function (type, msg, asError = TRUE)  :
    Could not resolve host: github.com; Host not found, try again

This error is displayed because R is trying to access on Intenet through a proxy.

Solution. How to install_github when there is a proxy

I am on CentOS 6.4 32 bit and am trying to cause a buffer overflow in a program. Within GDB it works. Here is the output:

    [root@localhost bufferoverflow]# gdb stack
    GNU gdb (GDB) Red Hat Enterprise Linux (7.2-60.el6_4.1)
    Copyright (C) 2010 Free Software Foundation, Inc.
    License GPLv3+: GNU GPL version 3 or later &lt;http://gnu.org/licenses/gpl.html&gt;
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.  Type &quot;show copying&quot;
    and &quot;show warranty&quot; for details.
    This GDB was configured as &quot;i686-redhat-linux-gnu&quot;.
    For bug reporting instructions, please see:
    &lt;http://www.gnu.org/software/gdb/bugs/&gt;...
    Reading symbols from /root/bufferoverflow/stack...done.
    (gdb) r
    Starting program: /root/bufferoverflow/stack
    process 6003 is executing new program: /bin/bash
    Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.107.el6_4.2.i686
    sh-4.1#

However when I run the program stack just on its own it seg faults. Why might this be?

Buffer overflow works in gdb but not without it

Can anyone explain what does Java do when `_JAVA_OPTIONS` Environment variable defined &amp; when application launched on the windows machine? 

Information about _JAVA_OPTIONS

<p>Can anyone explain what does Java do when <code>_JAVA_OPTIONS</code> Environment variable defined &#x26; when application launched on the windows machine?</p>


I have a problem resetting hours in Java. For a given date I want to set the hours to 00:00:00.

This is my code : 

    /**
         * Resets milliseconds, seconds, minutes and hours from the provided date
         *
         * @param date
         * @return
         */
        public static Date trim(Date date) {
            Calendar calendar = Calendar.getInstance();
            calendar.setTime(date);
            calendar.set(Calendar.MILLISECOND, 0);
            calendar.set(Calendar.SECOND, 0);
            calendar.set(Calendar.MINUTE, 0);
            calendar.set(Calendar.HOUR, 0);
    
            return calendar.getTime();
        }


The problem is that sometimes the time is `12:00:00` and sometimes it is `00:00:00` and when I query the database for an entity that was saved on `07.02.2013 00:00:00` and the actual entity time, that is stored, is `12:00:00` the query fails. 

I know that `12:00:00 == 00:00:00`! 

I am using AppEngine. Is this an appengine bug, problem or some other issue?  Or does it depend on something else?

Set time to 00:00:00

Can someone help me to understand what Java `CountDownLatch` is and when to use it? 

I don&#39;t have a very clear idea of how this program works. As I understand all three threads start at once and each Thread will call CountDownLatch after 3000ms. So count down will decrement one by one. After latch becomes zero the program prints &quot;Completed&quot;. Maybe the way I understood is incorrect. 

&lt;!-- language-all: java --&gt;

    import java.util.concurrent.CountDownLatch;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
         
    class Processor implements Runnable {
        private CountDownLatch latch;
         
        public Processor(CountDownLatch latch) {
            this.latch = latch;
        }
         
        public void run() {
            System.out.println(&quot;Started.&quot;);
             
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
             
            latch.countDown();
        }
    }

 // -----------------------------------------------------

    public class App {
    	 
    	public static void main(String[] args) {
    		 
    		CountDownLatch latch = new CountDownLatch(3); // coundown from 3 to 0
    		 
    		ExecutorService executor = Executors.newFixedThreadPool(3); // 3 Threads in pool
    		 
    		for(int i=0; i &lt; 3; i++) {
    		    executor.submit(new Processor(latch)); // ref to latch. each time call new Processes latch will count down by 1
    		}
    
    		try {
    		    latch.await();  // wait until latch counted down to 0
    		} catch (InterruptedException e) {
    		    e.printStackTrace();
    		}
    		 
    		System.out.println(&quot;Completed.&quot;);
    	}
    	 
    }

How is CountDownLatch used in Java Multithreading?

I was wondering what happens when you try to catch an StackOverflowError and came up with the following method:

    class RandomNumberGenerator {

        static int cnt = 0;

        public static void main(String[] args) {
            try {
                main(args);
            } catch (StackOverflowError ignore) {
                System.out.println(cnt++);
            }
        }
    }

Now my question:

Why does this method print &#39;4&#39;?

I thought maybe it was because `System.out.println()` needs 3 segments on the call stack, but I don&#39;t know where the number 3 comes from. When you look at the source code (and bytecode) of `System.out.println()`, it normally would lead to far more method invocations than 3 (so 3 segments on the call stack would not be sufficient). If it&#39;s because of optimizations the Hotspot VM applies (method inlining), I wonder if the result would be different on another VM.


&lt;b&gt;Edit&lt;/b&gt;:

As the output seems to be highly JVM specific, I get the result 4 using&lt;br&gt;
Java(TM) SE Runtime Environment (build 1.6.0_41-b02)&lt;br&gt;
Java HotSpot(TM) 64-Bit Server VM (build 20.14-b01, mixed mode)

&lt;br&gt;

&lt;b&gt; Explanation why I think this question is different from https://stackoverflow.com/questions/15083318/understanding-java-stack: &lt;/b&gt;

My question is not about why there is a cnt &gt; 0 (obviously because `System.out.println()` requires stack size and throws another `StackOverflowError` before something gets printed), but why it has the particular value of 4, respectively 0,3,8,55 or something else on other systems.


Why does this method print 4?

I am just having hard time to understand concept behind putting `wait()` in `Object` class.  For this questions sake consider if `wait()` and `notifyAll()` are in `Thread` class.

    class Reader extends Thread {
        Calculator c;
        public Reader(Calculator calc) {
            c = calc;
        }
    
        public void run() {
            synchronized(c) {                              //line 9
            try {
                System.out.println(&quot;Waiting for calculation...&quot;);
                c.wait();
            } catch (InterruptedException e) {}
                System.out.println(&quot;Total is: &quot; + c.total);
            }
        }

        public static void main(String [] args) {
            Calculator calculator = new Calculator();
            new Reader(calculator).start();
            new Reader(calculator).start();
            new Reader(calculator).start();
            calculator.start();
        }
    }
    
    class Calculator extends Thread {
        int total;
        public void run() {
            synchronized(this) {                     //Line 31
                for(int i=0;i&lt;100;i++) {
                    total += i;
                }
                 notifyAll();
            }
        } 
    }

My Question is that what difference it could have made? In line 9 we are acquiring lock on object c and then performing wait which satisfy the condition for wait that we need to acquire lock on the object before we use wait and so is case for notifyAll we have acquired lock on object of Calculator at line 31.


Concept behind putting wait(),notify() methods in Object class

I would like to write a method that would return a `java.util.List` of any type **without the need to typecast anything**:

    List&lt;User&gt; users = magicalListGetter(User.class);

    List&lt;Vehicle&gt; vehicles = magicalListGetter(Vehicle.class);

    List&lt;String&gt; strings = magicalListGetter(String.class);

What would the method signature look like? Something like this, perhaps(?):

    public List&lt;&lt;?&gt; ?&gt; magicalListGetter(Class&lt;?&gt; clazz) {
        List&lt;?&gt; list = doMagicalVooDooHere();

        return list;
    }

Content Type	Original Author	Original Content on Stackoverflow
Question	Madan	View Question on Stackoverflow
Solution 1 - Java	Demi Ben-Ari	View Answer on Stackoverflow
Solution 2 - Java	Vadzim	View Answer on Stackoverflow

Information about _JAVA_OPTIONS

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Buffer overflow works in gdb but not without it

Solution. How to install_github when there is a proxy

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