Develop Reference

Is source file and a package the same thing in Eclipse?

I am a complete beginner when it comes to Java. I recently picked up Head First Java and it says: "Put a class in a source file. Put methods in a class. Put statements in a method." When I open eclipse i started a new project called helloWorld, this created a project with a src folder(guessing this is the source file?), i then followed an eclipse tutorial from their website and it stated that i needed to first create a project, then a package, then a class in that package. What is the difference between a source file and a package?

A package more-or-less equates to a directory under your "src" folder in this case. Examples might include "com.project.ui" or "com.project.models" (and so there would be a "com" directory inside "src" and inside "com" you would have "project" and so on).
A source file is just that--it's an individual file that will live in one of those packages, probably named as "MyClass.java" where "MyClass" corresponds exactly to the name you give the one public class that the source file should contain.
BTW, if you will build your code with Maven, you should follow the suggested Maven directory structure--see this. In the case of Maven then, your java packages would start under "src/main/java" rather than under just "src" which is maybe what Eclipse will assume you want by default.
EDIT: Also take care to align the package you declare at the top of your Java source file with the package that it actually "lives in" on your filesystem--it's essential that these be in agreement. So, if your "MyClass.java" lives on the filesystem in com/projects/models, your package statement at the top of "MyClass.java" must be "package com.projects.models;" By convention package names will be all lowercase, class names will be upper and lower ("camel case") starting with a capital letter and method names start with a lowercase letter, but then are also camel case.

The following is a java source text:
package org.apache.twinkle;
public class Elfie {
...
}
It resides under a sources directory (generally src), and has a file path:
org/apache/twinkle/Elfie.java
(Directories org, apache, twinkle and file Elfie.java.)
So a package indicates some hierarchy and corresponds 1:1 with a directory.
The source file has a .java extension.
Paths should be case-sensitive. Package paths are hierarchical and generally follow the convention of starting with a reversed URL.
http://mit.com
package com.mit.mathlib.graphs;
http://univ-abu-dabi2.net
package net.univAbuDabi2.linguistics;
import com.mit.mathlib.graphs.GraphUtils;

Source file is complete Java code.
Package gather a several Java file under some issue like: GUI, server, login and etc.
Try to create several package and then go to the workspace to see what you got.
Also, when it comes to package issues, you also have the 'package' definition for class variables, which means that you are able to use this variable from other classes in the same package.

Configuring IntelliJ project

My problem is very simple to describe.
I've made a Class named Car and I let IntelliJ build the Car.class file.
After that I've made another Project which has a dummy class called Main which wrapps this Car object.
In the project structure I've added as an external library the folder which contains Car.class.
So basicly after declaring the Car member variable in my Main dummy class, IntellJ normaly suggests me to import Car which is shown in the picture below.
Picture1
When I choose to import Car class it directly writes down the package before the Class name (not the usual import statement) and the import fails as shown on this picture.
Picture2
(note: the reason it states org.dino.test.pojos is because Car class package is org.dino.test.pojos)
The project setup is shown below.
Picture 3
Does someone know how to setup this project structure so such things work?

The fact that IntelliJ has marked the org directory as the library home is suspicious- I suspect that you have defined the classes in the library as the org subdirectory rather than the JAR or classes directory itself.
You also have a folder structure that is inconsistent with your package structure.
When you define the library, select the testLibrary directory/JAR rather than one of the directories inside it. Also, ensure that the folder structure inside your library matches the Java package of the class within it.

Java: silly newbie issue about path used in import statement

I'm working through the example here:
http://www.vogella.com/articles/JavaPDF/article.html
In my file, I've got:
package com.mycompanyname.mydirectory;
import com.mycompanyname.OneOfMyClasses;
import com.itextpdf.text.Document;
...
public class MyClass {
...
}
Everything is working fine. What I don't understand is that since I just copied the import statement directly from the link above for the iText portion -- why does com.itextpdf.text.Document work?
I mean, if I look in directory com.mycompanyname I can see OneOfMyClasses.java there.
But in the com directly, there is no itextpdf directory (although maybe my user doesn't have permission to see it(?)).
Hoping someone can help me understand what I'm missing here. Doesn't the import point to a specific directory that I should be able to see the class? Is there a different com directory somewhere that iText is using, and com.itextpdf.text points to there? (if so, where's the directory located)?
I installed the jar file for iText in the lib folder as per usual, and made sure it was included in the classpath.

Those classes are inside a JAR file that is added to the classpath:
Create a new Java project "de.vogella.itext.write" with the package "de.vogella.itext.write". Create a folder "lib" and put the iText library (jar file) into this folder. Add the jar to your classpath.
import statements will look inside whatever directory trees are in the classpath, which includes the current directory at compilation time (tipically the src/ directory in your project) as well as any directory specified through environment variable or JVM startup parameter. See this about the classpath.
EDIT
You do need the imports whenever you use classes across packages. Every public class/interface you define is in a package. If whatever you are referencing belongs to another package, you need to import it.
JARs are zip files that contain directories and files inside. It's the same as plain directories and files, only packed.

It comes from the iText dependency (jar) you added in an earlier step.

Not necessarily - you could also import from libraries, etc.
In fact, Java will try to search through the classpath. Here is some helpful documentation.

That class is most probably imported in a JAR library. Inside such JAR file, the class files are kept in exact package/folder structure as you use when importing them.

How to generate package structure from standalone *.java source files?

I've been searching for answer for my problem but I can't find some relevant information, so I'm asking. I've directory which contains thousands of Java classes with source code (*.java files). Each of those files contains information to what package the file belongs, its classnames + code itself of course. I need to find some function of the Eclipse IDE (or maybe of another IDE) which is able to reconstruct packages under the 'src' directory based on the information in the class files and bring to me a good Java project structure so the restored packages and its classes can be easily imported into a new Java project then. Creating the structure of packages manually would take me (maybe) lot of days...
For clarification:
I have:
directory which contains: 1.java, 2.java, 3. java, n.java...
I need:
directory which will contain:
[src] -> [package_1] -> [1.java, 2.java, etc...]
...
[src] -> [package_m] -> [3.java, n.java]
I think this must be possible somehow as the each class file contains information to which package it belongs actually.

Just if you find no better solution: At least you can import all sources into a project in Eclipse and have Eclipse move each file to the right package by means of using the quick fix for each problem. You still need to press 3 keys per wrong package declaration, but it saves you from fiddling with files and folders.

Java Package Vs Folder-Structure? what is the difference

I would like to know What are the difference between folder-structure and package used in Eclipse IDE for Java EE development.
When do we use which one and why?.
Whats should be the practice
create a folder structure like src/com/utils and then create a class inside it
create a package like src.com.util and then create a class inside it
which option would be better and easy to deploy if i have to write a ant script later for deployment ?
if i go for the folder-structure will the deployment is as easy as copying files from development to deployment target ?

If you configured stuffs correctly. Adding a folder inside src, is same as adding a package from File > New Package.
So, it's up to you, whatever feels comfortable to you -- add a folder or create a package. Also, when you put stuffs under src the package name starts from subfolder. So, src/com/naishe/test will be package com.naishe.test.

Basically there is no difference, both are the same.
In both the cases, the folder structure will be src/com/utils.
and in both the cases, you will need to mention
package com.utils;
as first line in the class
Since it doesn't have any difference practically, it won't make any difference to ant script.

"Packaging helps us to avoid class name collision when we use the same class name as that of others. For example, if we have a class name called "Vector", its name would crash with the Vector class from JDK. However, this never happens because JDK use java.util as a package name for the Vector class (java.util.Vector). So our Vector class can be named as "Vector" or we can put it into another package like com.mycompany.Vector without fighting with anyone. The benefits of using package reflect the ease of maintenance, organization, and increase collaboration among developers. Understanding the concept of package will also help us manage and use files stored in jar files in more efficient ways."
check out http://www.jarticles.com/package/package_eng.html for more information on packages

create a package like 'src.com.util'
That sounds like a mistake. The package name should be 'com.util', and 'src' is the name of the source folder.
Other than that, I fail to see what the difference is between your two choices. The result is the same, right? Just different steps in the GUI to arrive at it. The wizard to create a new package in Eclipse is just a wrapper around creating the appropriate folder hierarchy within a source folder.
You don't need to create empty packages at all, you can directly create classes (the package will be created automatically if it does not already exist).

A package is automatically "source folder" where folder is just a normal folder.
When you compile an Eclipse project, all files in source folders are compiled but not in regular folders (unless those regular folders a)

folder structure or to be specific source folder in eclipse is meant just for eclipse but package is universal irrespective of any editor..