Monday, December 11, 2017

How to comment uncomment single line and block of code in Java - Eclipse Tips Tricks

Knowing Eclipse shortcut to comment and uncomment single line or block of code can save you lot of time while working in Eclipse. In fact I highly recommend every Java programmer to go through these top 30 Eclipse shortcut and  10 java debugging tips in Eclipse for improved productivity.  If you are Java programmer, coding in Eclipse and want to comment and uncomment single line or block of code quickly you can either use ctrl + / to comment a single line and subsequently uncomment a commented line. If you want to comment a block of code or a complete method, you have two option you can either line comment (//) all those selected lines or block comment (/* */) those lines.

For line comment multiple line, select multiple line and press ctrl + /, it will put // in front of every line. For block commenting in Eclipse, first select all the lines or code block you want to comment and then enter ctrl+shift+/ it will put /* on first line and */ on last line. Here is better illustrated example of commenting and uncommenting Java code in Eclipse IDE :

Eclipse shortcut to comment one line or block code in Java

Suppose I have a following method :

public void printHello(){

and I want to comment line which is printing HelloWorld, just put the courser on that line and type ctrl+/ , you will see following line :

public void printHello(){
//    System.out.println("HelloWorld");

How to comment uncomment java code in Eclipse IDEIf you want to uncomment that same line, keep the cursor on same line and type again ctrl+/, it will uncomment that line.

If you want to comment whole method , first select whole method and then type ctrl+/, this will line comment all selected line as shown below :

//public void printHello(){
//    System.out.println("HelloWorld");

If you want to block comment whole block than type ctrl + shift + / and it will put  /* and */ on first and last line, as shown below :

/*public void printHello(){

This Eclipse shortcut for commenting and uncommenting Java code will surely help you save few keystrokes and improve your speed while working in Eclipse. To learn more Eclipse comments short cuts see Top 30 Eclipse keyboard Shortcuts for Java programmer.

Further Learning
Beginners Eclipse Java IDE Training Course
Eclipse Debugging Techniques And Tricks
The Eclipse Guided Tour - Part 1 and 2

Other Eclipse tutorials for Java programmer


Unknown said...

I Am Facing A Very Unique Problem Rare For Any To Face When I Am Compiling And Running My Java Code Its Getting Compiled And Shows Output In Text-pad/ Eclipse Editor But When I Am Running It Through saved in a textpad calling in DOS Of Win XP Professional. It Compiling Successfully But When Trying To Run It Though Window's DOS It Throws _______My Code States Like This_______
public class HelloWorld {

public static void main(String[] args[]) {
System.out.println("Hello, World");


Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld
Caused by: java.lang.ClassNotFoundException: HelloWorld
at Method)
at java.lang.ClassLoader.loadClass(
at sun.misc.Launcher$AppClassLoader.loadClass(
at java.lang.ClassLoader.loadClass(
at java.lang.ClassLoader.loadClassInternal(

Anonymous said...


The java classpath is not set correctly when you are trying to run your java program directly on the command line, hence the self-evident 'NoClassDefFoundError'.

Post a Comment