This chapter is not something that you need to memorize but, from the exam point of view, this is a pretty important chapter. We will be covering some tips and tricks that can help you prepare better for the exam and get certified successfully.
Another good news is, we have already covered all you need to know to pass the SCWCD Exam. This is going to be the last chapter in this series (Of
Showing posts with label tips. Show all posts
Showing posts with label tips. Show all posts
Spring Framework Dump Java Program Output to a Text File
java Classname
When you append a small greater than symbol at last followed by the file name. All the output will be dumped. Here will be the new command then.
java Classname >out.txt
*Here the file name is out.txt.
In this way we can dump program output.
You'll have to note that not every thing is dumped into the file, instead what is printed using the program using the standard print methods is printed. The input that the user types or any exceptions that occur are not dumped into the file.
Spring Framework Anonymous inner class in Java with Example
We know that one cannot create an object for either an abstract class or an interface directly but can do it indirectly. One of the indirect way of doing this is writing a class that extends the abstract class or if it is an interface, writing a class that implements this interface. Then we'll create the object for that class and call it in the name the interface or it's super abstract class. Writing a class each time is a headache. So, it's better if we can just write a class with in the class itself.
You might encounter the concept of nested classes this time. But let's try the anonymous inner classes. I've previously used the concept of anonymous inner classes very previously in many posts especially in Threading and Swing concepts. Now let us see an example of this here.
abstract class AE
{
int n;
public AE(int n)
{
this.n=n;
}
public abstract void myMethAE();
public void myMethBE()
{
System.out.println("My Meth BE | n:"+n);
}
}
class AnonymousExample
{
public static void main(String args[])
{
AE a=new AE(2){
public void myMethAE(){
System.out.println("myMethAE | n:"+n);}
public void myMethBE(){
System.out.println("My Meth BE");
}
};
a.myMethAE();
a.myMethBE();
}
}
Output
myMethAE | n:2
My Meth BE
Explaining the code
new AE(2){//code}; Invoke the constructor in the class AE taking an int type variable as parameter.Open the braces, start implementing the abstract methods/override the existing ones (if necessary).public void myMethAE(){} Write the implementation code for myMethAE in the braces (i.e. develop the body of this method).In the same way for myMethBE() but here the method is overriden.
Note: Not only with abstract classes, you can also work out things with interfaces i.e. you can provide the implementation code for the methods defined in an interface in the same way. I have already done in many of my previous posts and Using JProgressBar with Thread class is one of them. Here the Runnable interface is implemented in the style above.
So, i think you are now clear about how to write anonymous inner classes in Java with this enunciating example. Drop a comment for queries.
Spring Framework 3 Ways of writing main() in Java
Routine way..
public static void main(String args[]){}
Pushing the square before
public static void main(String[] args){}
Three dot's can make it!
public static void main(String ...args){}
Hmm, you might also know that you can also change the parameter name if you don't like keeping it args whatsoever, this is a common known fact and i think i don't need to tell you.
Spring Framework Pre Check web.xml for Errors in Servlets
As web.xml is an xml file, the default application for xml files is Internet Explorer, so open web.xml in Internet Explorer. That's it.
See following, i had intentionally written an error in web.xml (not properly closing the
<web-app>.
<web-app>
<servlet>
<servlet-name>mys</servlet-name>
<servlet-class>CookieExample</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>mys</servlet-name>
<url-pattern>/co</url-pattern>
</servlet-mapping>
<web-app>
When i open this in Internet Explorer, the screenshot will look like..
 |
| web.xml error in Internet Explorer |
When i write it correctly, closing the tag properly, it will look like..
 |
| web.xml is displayed in Internet Explorer |
Unlike the previous screenshot, in this screenshot you have the web.xml correctly displayed which means that the xml file is well parsed with no errors.
However, errors that are not related to the syntax such as change servlet name in tags i.e. different servlet names in servlet-mapping and servlet tags cannot be identified unless you are familiar with.
This is just a tip that helps you detect xml parsing related errors. Hope this helps.
Spring Framework How to compile Java files to external directory
javac -d EXTERNAL_DIR SRC_FILEHere are some examples,
javac -d D:\classes MyClass.javajavac -d D:\classes E:\java\MyClass.javaNote that
-d represents a directory and that you'll have to specify a directory to store the class files but not a file. Also, the directory where the class files should be stored must exist. The source file of course must exist first of all.You can see javac -help for more options.
Spring Framework Mapping network drive in Windows XP and 7 – net use command Example
Mapping network drive in Windows XP or Windows 7 is much easier and faster by using command line than by doing it on Windows explorer. If you have been working in Windows environment with bunch of Windows 2000 or 2003 servers and your job requires frequent access, copy or paste from local machine to those remote machine than mapping them as network drive is the best option. You can use mapped network drive as any other folder which makes job of copy paste very simple. Though windows provides multiple ways to map network drive, I prefer to use command line i.e. "net use" command to map my windows network drives. This works in Windows XP and should work in Windows 7 without any fuss, its way faster than accessing every singlet node on network to reach desired fast and In order to use this you just need to change of network drive. In our last post on Windows operating system we have seen How to find IP address from hostname and this article we will see how to map remote host as network drive in windows XP. Any way enough talking, let's see command to map network drive in windows:
Spring Framework How to take a screenshot using Robot
BufferedImage createScreenCapture(Rectangle rect)This method takes java.awt.Rectangle as parameter. You can use any of the seven constructors of this class to create it's object, however i don't recommend the first one which just creates a Rectangle object that is invisible when used to capture the screen. All the constructors do the same thing, their parameters differ instead. For brevity and ease, in this post i will be using the third constructor which takes 4 integer values which represent the x, y, width, height respectively. The returned java.awt.image.BufferedImage object is returned. This is used to write the image to a file. Here is the example.
import java.util.*;
import java.awt.*;
import java.awt.image.*;
import javax.imageio.*;
import java.io.*;
class ScreenCapture
{
public static void main(String args[]) throws Exception
{
// Throws AWTException
Robot rb=new Robot();
Scanner s=new Scanner(System.in);
System.out.println("Enter the x,y,width,height of capture");
int x=s.nextInt();
int y=s.nextInt();
int width=s.nextInt();
int height=s.nextInt();
String file=s.next();
// Get the BufferedImage object for writing to a fiel
BufferedImage bim=rb.createScreenCapture(new Rectangle(x,y,width,height));
/* Throws IOException
* Write in PNG format. You can choose whatever format you want.
* Write the image.
* If you know the extension of the format.
* Write to a file specified
*/
ImageIO.write(bim,"PNG",new File(file));
}
}
Sample output of ScreenCapture
Spring Framework How to open JNLP files in Windows?
We might be confused!
At times the JNLP files may not be automatically associated with the required program. This happened to me most of the times. We are confused because there are javaw.exe, java.exe, javaws.exe a lot of exe files in the bin directory and we might not know which will open this. Whatever the reason may be leave it. We have the solution, so let's solve.
What is the file that can open JNLP file?
javaws.exe called as Java Web Start Launcher (TM) can open a JNLP file.
Where is it located?
It is located in the bin directory which is present in the jdk directory. For example,
C:\Program Files\Java\jdk1.6.0_43\bin\javaws.exeHow to associate this program?
Right click on the JNLP file and click on Open with... (if you find this on the context menu itself). If it is a present as menu Open with -> Choose default program.
Whatever you do, try to get the Open with dialogue box, and then click Browse.. go the bin directory, select javaws.exe and hit enter.
If you still didn't get how to open a JNLP file, feel free to drop a comment and i'll be able to respond as soon as possible.
Spring Framework Swapping two variables in Java
import java.util.*;
class SwapDemo
{
public static void main(String args[])
{
Scanner s=new Scanner(System.in);
System.out.println("Enter 2 numbers to
swap");
int a=s.nextInt();
int b=s.nextInt();
swap(a,b);
}
public static void swap(int a,int b)
{
// Store a in a temporary variable
int temp=a;
// Store b variable value in a
a=b;
// Store temp (a original) value in b
b=temp;
// Print the variables
System.out.println("a is "+a+" & b is "+b);
}
}
Sample Output
Enter 2 numbers to swap
8
7
a is 7 & b is 8
Explanation
The logic is very simple. Everything here is done in the swap() method which take two parameters of type int (here) [You can take variables of any type and swap]. From the comments, it is obvious that first, the value in he variable a is stored in temp and the value of b is stored in a. Now a contains the value in b and temp contains the value in a. Now all that is left is store the value of a in b. For this we'll use the initially stored value of a which is in temp and assign the value to b.
When we print the variables we'll find that the variables are swapped i.e. their values are interchanged. Note that, as call-by-value takes place here the effect is circumscribed with in the
swap() method only. The original a & b are not swapped. For that to be done, write the swap code in the main() itself.Spring Framework How to Increase Console Buffer Size in Eclipse IDE - Output and Debug Console
By default Eclipse IDE has limit on console output, also known as console buffer size. Which means, your Eclipse console will overfill quickly, if you are running a Java server program, which usually do lot of logging. Once this happen, you start losing logs. whenever new logs appear, equal number of oldest logs are truncated. Thankfully there is a way to increase output capacity in Eclipse IDE. I discovered this tip, on my search of Eclipse productivity tips e.g. Eclipse shortcuts and settings to organize import. You can increase console buffer size, which is specified in characters by using Eclipse preferences. Eclipse Indigo has default console buffer size as 250000 characters. Eclipse also provides a check box Limit Console Output to put enforce limit on console output, In order to increase console output either you can unchecked this box or you can increase console buffer size. I usually unchecked, Limit Console Output to avoid guessing a good number for console buffer size.
Spring Framework Compile All Java Programs in a Directory
javac filename.java
To compile all the java files in a directory, we can simply write,
javac *.java
The above command compiles all the java files (the files that end with .java extension). Isn't that simple? It helps when your project source files are in the same directory or even when working out with servlets where every source file usually exists in the same folder.
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