JavaRoach

How To Add JLabel To JApplet

2010-06-02T14:43:21Z



package javaroach;
import java.awt.Color;
import java.awt.Container;
import java.awt.GridLayout;
import java.awt.LayoutManager;
import javax.swing.JApplet;
import javax.swing.JLabel;
public class HowToAddJLabelToJApplet extends JApplet {
// Declaration
private Container container;
private LayoutManager layoutManager;
private JLabel label1;
private JLabel label2;
private JLabel label3;
private JLabel label4;
private JLabel label5;
private JLabel label6;
private JLabel label7;
public HowToAddJLabelToJApplet() {
// Instantiation
layoutManager = new GridLayout(7, 1);
label1 = new JLabel("A Simple Label");
label2 = new JLabel("A Label with LEFT alignment", JLabel.LEFT);
label3 = new JLabel("A Label with CENTER alignment", JLabel.CENTER);
label4 = new JLabel("A Label with RIGHT alignment", JLabel.RIGHT);
label5 = new JLabel("A Label with LEADING alignment", JLabel.LEADING);
label6 = new JLabel("A Label with TRAILING alignment", JLabel.TRAILING);
label7 = new JLabel();
container = getContentPane();
// Location
container.setLayout(layoutManager);
container.add(label1);
container.add(label2);
container.add(label3);
container.add(label4);
container.add(label5);
container.add(label6);
container.add(label7);
// Decoration
container.setBackground(Color.yellow);
label7.setHorizontalAlignment(JLabel.CENTER);
label7.setForeground(Color.blue);
label7.setText("Text added with setText");
}
}

How To Use Generic Servlet

2010-06-02T15:56:47Z

GenericServlet is protocol independent. The code shows how to use it.



package javaroach;
import java.io.IOException;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class HowToUseGenericServlet extends GenericServlet {
public void service(ServletRequest arg0, ServletResponse arg1)
throws ServletException, IOException {
// Handle the request here
System.out.println("The request will be handled here");
}
}

How To Use HTTP Servlet

2010-06-02T15:59:18Z

To handle HTTP protocol request, we need to use HTTPServlet. Depending on which HTTP protocol is calling the servlet (GET or POST), its respective method will be called.



package javaroach;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class HowToUseHTTPServlet extends HttpServlet {
public HowToUseHTTPServlet() {
}
public void doGet(HttpServletRequest request, HttpServletResponse response) {
// if this is printed, HTTP GET protocol is used to call this servlet
System.out.println("HTTP GET protocol is used to call this servlet");
}
public void doPost(HttpServletRequest request, HttpServletResponse response) {
// if this is printed, HTTP POST protocol is used to call this servlet
System.out.println("HTTP POST protocol is used to call this servlet");
}
}

What And How Do I Debug A Null Pointer Exception

2010-06-02T14:51:46Z

Null pointer exception usually occurs when an object variable is either set as null or is not initialized. Note that primitives such as int, long, float, double, char, boolean, short and byte are not object hence the above rule does not apply. Calling a method from the object that is null will caused it to blow up during run time and throw a NullPointerException.



package javaroach;
public class ShowHowNullPointerExceptionHappens {
public static void main(String[] args) {
String ferrari = "Cool!";
String camry = null;
System.out.println(ferrari.substring(0, 4));
camry.substring(1, 1);
}

}

Here’s the output.



Cool

Exception in thread "main" java.lang.NullPointerException

at javaroach.ShowHowNullPointerExceptionHappens.main(ShowHowNullPointerExceptionHappens.java:10)

How To Make Thread Sleep

2010-06-02T14:55:00Z

This will make the application to wait or sleep for 10 seconds before printing the statement.



package javaroach;
public class MakeThreadSleep {
public static void main(String[] args) {
try {
// sleeps for 10000 milliseconds or 10 seconds
Thread.currentThread().sleep(10000);
System.out.println("Thread slept for 10 seconds before printing this.");
} catch (InterruptedException e) {
e.printStackTrace();
}
}

}

How To Write To Properties File

2010-06-02T14:30:02Z



package javaroach;





import java.io.FileNotFoundException;


import java.io.FileOutputStream;


import java.io.IOException;


import java.util.Properties;





public class WriteToProperties {





    public static void main(String[] args) {


        // Write properties file


        Properties properties = new Properties();


        


        try {


            properties.setProperty("best", "JavaRoach is the best Java website!");


            properties.store(new FileOutputStream("other.properties"), null);


        } catch (FileNotFoundException e) {


            e.printStackTrace();


        } catch (IOException e) {


            e.printStackTrace();


        }


    }





}

How To Read From Properties File

2010-06-02T14:20:18Z

This will read from a properties file and using key value to get the data.



package javaroach;





import java.io.FileInputStream;


import java.io.FileNotFoundException;


import java.io.IOException;


import java.util.Properties;





public class ReadFromProperties {





    public static void main(String[] args) {


        // Read properties file


        Properties properties = new Properties();





        try {


            properties.load(new FileInputStream("anyname.properties"));


            


            // use key to get the value


            // this should print "JavaRoach is great"


            System.out.println("JavaRoach " + properties.getProperty("javaroach"));


        } catch (FileNotFoundException e) {


            e.printStackTrace();


        } catch (IOException e) {


            e.printStackTrace();


        }


    }





}

The above will print “JavaRoach is great”.

Introduction To Generics

2010-01-11T15:22:56Z



List myIntList = new LinkedList();

myIntList.add("value");

Integer x = (Integer) myIntList.iterator().next();

The code above is a common programming error. It will not throw an exception on compilation but will definitely blow up during run time. To prevent this from happening, we can use generics to specify the type that is accepted by the List. This is known as generics. The code below uses generics.



List myIntList = new LinkedList();

myIntList.add(new Integer(0));

Integer x = myIntList.iterator().next();

How To Format Date

2010-06-02T15:09:35Z



package javaroach;
import java.text.SimpleDateFormat;
import java.util.Date;
public class HowToFormatDate {
public static void main(String[] args) {
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("dd/MM/yyyy");
Date date = new Date();
System.out.println(simpleDateFormat.format(date));
}
}

Checking Whether Port Is Running From Command Prompt

2010-06-02T15:15:50Z

Here’s another useful non java tips. This is to check whether a server port is up and running on your command prompt.

It will look something like this.

The command above checks whether port 80 from server 127.0.0.1 is up and running. If the port is running, then the screen will be cleared. If not, an error message will appear.