Tuesday, February 26, 2013

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");
VMManagement vmManagement = (VMManagement) jvmField.get(runtimeMXBean);
Method getProcessIdMethod = vmManagement.getClass().getDeclaredMethod("getProcessId");
Integer processId = (Integer) getProcessIdMethod.invoke(vmManagement);
System.out.println("################    ProcessId = " + processId);
} catch (Exception e) {


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++) {
end = System.currentTimeMillis();
System.out.println("StringBuilder concatenation x " + runfor[i] + " times: " + (end - start) + " miliseconds");


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

Monday, January 28, 2013

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

$ git push origin 7605596d45d2e3812da1e22db447fc6f1fe6f876:Dev-5.0

Friday, January 25, 2013

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

Thursday, January 24, 2013

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

Tuesday, January 22, 2013

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.

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

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

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

Other sources: