StringBuilder with modern compilers

Modern Java compiler convert your + operations by StrinBuilder's append. I mean to say if you do str = str1+sr2+str3 then compiler will generate following code

StringBuilder sb = new StringBuilder();
str = sb.append(str1).append(str2).append(str3).toString();

So now its more of matter of choice than performance benefit to use + or StringBuilder :)

JVM: Finding the process id

package com.kk.memory.tool;

import sun.management.VMManagement;
import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class FindJavaProcessId {

public static void main(String[] args) {

try {
RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
Field jvmField = runtimeMXBean.getClass().getDeclaredField("jvm");
jvmField.setAccessible(true);
VMManagement vmManagement = (VMManagement) jvmField.get(runtimeMXBean);
Method getProcessIdMethod = vmManagement.getClass().getDeclaredMethod("getProcessId");
getProcessIdMethod.setAccessible(true);
Integer processId = (Integer) getProcessIdMethod.invoke(vmManagement);
System.out.println("################    ProcessId = " + processId);
} catch (Exception e) {
e.printStackTrace();
}
}

}

String vs StringBuilder performance trade-offs

public class StringTest {

public static void main(String[] args) {

int[] runfor = { 10, 100, 1000, 10000 };

for (int i = 0; i < runfor.length; i++) {
long start = System.currentTimeMillis();
String s = "";
for (int j = 0; j < runfor[i]; j++) {
s += "Hello" + "--" + "World!!!";
}
long end = System.currentTimeMillis();
System.out.println("String concatenation x " + runfor[i] + " times: " + (end - start) + " miliseconds");

start = System.currentTimeMillis();
StringBuilder sb = new StringBuilder();
for (int j = 0; j < runfor[i]; j++) {
sb.append("Hello");
sb.append("--");
sb.append("World!!!");
}
end = System.currentTimeMillis();
System.out.println("StringBuilder concatenation x " + runfor[i] + " times: " + (end - start) + " miliseconds");
}
}
}

Results:

String concatenation x 10 times: 0 miliseconds

StringBuilder concatenation x 10 times: 0 miliseconds

String concatenation x 100 times: 1 miliseconds

StringBuilder concatenation x 100 times: 0 miliseconds

String concatenation x 1000 times: 15 miliseconds

StringBuilder concatenation x 1000 times: 1 miliseconds

String concatenation x 10000 times: 1143 miliseconds

StringBuilder concatenation x 10000 times: 3 miliseconds

Pushing a specific commit to repository

git status says:

$ git status
# On branch master
# Your branch is ahead of 'origin/master' by 2 commits.

You want to git push only one of those commits to the public repo. Here’s how:

First use git log to get the commit hash of the commit you want to push. Then:

$ git push origin <thelonghash>:master

example:
$ git push origin 7605596d45d2e3812da1e22db447fc6f1fe6f876:Dev-5.0

Viewing Unpushed Git Commits

It was useful for me to avoid unnecessary commits with a push.

git log origin/master..HEAD

You can also view the diff using the same syntax

git diff origin/master..HEAD

Source:  http://stackoverflow.com/questions/2016901/viewing-unpushed-git-commits

GIT: reverting a second commit of the push from central repository

Have you ever come across the issue, where you have pushed your code to a central repository but unknowingly old commit also has been pushed which is not required any more.

In general, If you want to revert a last commit:

$ git revert d768b8d6a709ba5524e2cf68915d718b9e9ae0bf


In your last push, you have pushed two commits and imagine second commit now you want to roll back,

$ git revert a768b8d6a709ba5524e2cf68915d718b9e9ae0be

fatal: Commit 137ea95 is a merge but no -m option was given.

You will come across above issue,

To resolve that, we need use -m option with order of a commit. Like below,

$ git revert a768b8d6a709ba5524e2cf68915d718b9e9ae0be  - m 2

This will revert second commit which you have made.

Source:  http://gitready.com/intermediate/2009/03/16/rolling-back-changes-with-revert.html

Eclipse debug configuration setting and reading

 Here is the way to specify the debug configuration parameters through VM arguments in eclipse.

In VM arguments section, as you can see I have passed following debug parameter.
-Dkony.debug=true


These parameters I can read in the following way in Java.

String isdebug = System.getProperty("kony.debug");
Boolean DEBUG_MODE = new Boolean(isdebug);

if(DEBUG_MODE) {
        System.out.println("My application is running in debug mode");
      //Do your action here!!
}


Other sources:
http://www.avajava.com/tutorials/lessons/whats-the-difference-between-program-arguments-and-vm-arguments.html