Import Statement in Java

I have one question about import of packages and classes. If I import java.awt.** why can't all the packages starting with java.awt get imported.For example java.awt.color.* or java.awt.font doesn't get imported. I didn't get why so and if so then why these classes were prefixed with java.awt. Same case happened to me when I imported java.util.* and didn't find java.util.concurrent.locks.Lock get imported. There must be some reason behind this. But I don't know. Can anyone please let me know ?
--Prasad
Edited by: Prasad_Kumbhare on Oct 1, 2007 7:55 PM

flounder wrote:For me:
Boredom, it gives me something to do.
Reward at imparting my knowledge onto others. When I was at uni I got some part time work as a tutor helping 1st and 2nd year students with their prac sessions and tutorials. I enjoyed being able to mould young minds. Plus, with all the subliminal messages I planted, one day I will rule the world. OK that last bit wasn't true. I want to rule the universe!That's very noble Mr Flounder, so thanks again.
I imagine if you want to rule the universe it makes sense to achieve this goal via a platform independant language. But does Java run on differant planets?
S

Similar Messages

Import statement in .java files and .jsp files

Guys I have few mysteries about this import statement.
Please correct me if I am wrong.
1)Suppose if I have a folder c:\SourceFolder it has one.java and two.java files.If I compile one.java then one.class files is created in c:\ClassFolder .Now two.java uses one of the method of one.java,and without using import statement I am able to compile two.java, and two.class file is created in c:\ClassFolder.I assume that the path of one.class was taken from the CLASSPATH environment variable,hence I there was no need for import statement .........am i right ?
BUT... in My.jsp,which is in C:\JspFolder, if I want to use one.class,then I have to specifically import the class I want to use.That is i have to say
<%@page import="one"%>
and since the classpath is C:\ClassFolder ,it finds one.class in the C:\ClassFolder.(Note that My.class is created in a folder different from c:\ClassFolder )
But I am wondering why was there no need for me to import one.class in two.java.
(Note I am using JDeveloper and Apache server)
Please help.
In this case the pSo I am wondering in JSP why it doesn't take the class I am looking for from the classpath .
Help.

You have to understand Java scoping rules. In the 1st scenario with the two Java files I am guessing neither one of them begins with a package statement. This means that they belong to the default package. When you compile the compiler uses the classpath to resolve method calls looking in the default package since there was no import statement specified in two.java. JSP is a little different. Now I just read this here in these forums a couple of days ago. Since the classfiles generated from the JSP files are not in the CLASSPATH they are loaded by a different classloader. This is why you have to import all references to all classes in the default package.

Import statement in .java files and .jsp files ..correction

Guys I have few mysteries about this import statement.
Please correct me if I am wrong.
1)Suppose if I have a folder c:\SourceFolder it has one.java and two.java files.If I compile one.java then one.class files is created in c:\ClassFolder .Now two.java uses one of the method of one.java,and without using import statement in two.java I am able to compile two.java, and two.class file is created in c:\ClassFolder.I assume that the path of one.class was taken from the CLASSPATH environment variable,hence I there was no need for import statement .........am i right ?
BUT... in My.jsp,which is in C:\JspFolder, if I want to use one.class,then I have to specifically import one.class in My.jsp .That is i have to say
<%@page import="one"%>
in My.jsp.
and since the classpath is C:\ClassFolder ,it finds one.class in the C:\ClassFolder and MyJsp is compiled sucessfully.(Note that My.class is created in a folder different from c:\ClassFolder )
But I am wondering why was there no need for me to import one.class in two.java.
(Note I am using JDeveloper and Apache server)
Please help.

It has to do with packages. Most java classes are in a package, the name of which must conform to its place on the filesystem relative to the classpath. By that I mean that if you have com.mystuff.One.java, it must be in a folder com/mystuff where com is located somewhere in the classpath.
What you've done is a little different. I'm assuming a couple of things:
1. you have no package declaration at the top of one.java or two.java
2. you have the current directory "." in your classpath.
Java has the concept of the "default package", which covers classes without a declared package, and in your case is the current directory.
So when you're in c:\sourcefolder and run the compiler, then "."="c:\sourcefolder", and that directory is part of the default package. No import statements are necessary for classes that are in the same package. This is why two.java can call methods in one.java without an import statement.
When you run your jsp, the "current directory" part of your classpath is not c:\sourcefolder, but some other value (probably the directory you start your jsp engine from) You will have to import all non-java-library classes because the jsp itself becomes a java class, with a package that is determined by the jsp engine.

Why the need of "import" statements for Java base code?

If for documentation purposes, a compiler option to produce an "import list" would have been sufficient.

import statements act as really simple namespaces.
Instead of the programer having to specify:
java.io.File f = new java.io.File("c:\\");
the code can have a 'namespace' added to do the following:
import java.io.file;
File f = new File("c:\\);
it's a way of getting around similiarly named classes, but still have the ability to drop the 'java.io.' part.

Executing db2 import statement from java

we have developed an web application using J2EE technology on websphere and DB2 as a backend.
I have to now develop a utility for data uploading from Excel to DB2. we can do it using IMPORT statement now i want to know is it possible to execute IMPORT statement from JSP/ Servelet and using javabeans.

Yes, it is possible :-)

Import statement and directory structure

First of all, sorry for such a long post, I believe part of it is because I am unsure of the concept of importing in Java. Secondly, Thanks to anyone who can ultimately enlighten me to the concept of import. I did ask this question before in the "erorr and error handling" forum, and the people who have helped me there did a great job. But, I believe I require a little more clarification and thus have decided to post here.
Anyhow, my question..
Could someone explain to me the concept of the import statement, or direct me to a webpage with sort of explanation for newbies? For some reason, I am having a hard time grasping the concept.
As I understand it, the import statement in Java, is very similar to the namespace keyword in C. That is to say, import doesn't actually "import" any source code, the way that the #include statement does in C.
So I suppose what my question is, say I have a java class file like below:
//filename: sentence.java
//located: c:\school\csc365
package csc365;
class sentence
//some variables here..
//some constructor here..
//some methods here..
And some sample program like the one below which implements the above..
//filename: test.java
//located: c:\school\csc365
import csc365.*;
import java.io.*;
class test.java
//creates some sentence object
//uses the object's methods
//some other things.
As I understand it, the test.java file should not compile because the csc365 package is not in the correct directory. (assuming of course, the classpath is like c:\school\csc365;c:\school )
But, ... where then should the sentence.java be located? In a subdirectory of c:\school called csc365 (i.e c:\school\csc365\) ?
And thus that would mean the test.java file could be located anywhere on the hard drive?
I suppose, I just need a little clarification on the correlation between a package's "name" (i.e package csc365; ) and its corresponding directory's name, and also how the javac compiler searches the classpath for java classes.
..So, theoretically if I were to set the classpath to look in every conceivable directory(provided the directory names were all unique) of the harddrive, then I could compile a test.java anywhere?
As a note: I have been able to get the test.java file to compile, by leaving out the import statement in the test.java file, and also leaving out the package statement for the sentence class, but I assume this is because the files are defaulted to the same package?

Hi Mary,
No, import isn't analogous to C++ namespace - Java package is closer to the namespace mark.
import is just a convenience for the programmer. You can go your whole Java career without ever writing an import statement if you wish. All that means is that you'll have to type out the fully-resolved class name every time you want to use a class that's in a package other than java.lang. Example:
// NOTE: No import statements
public class Family
   // NOTE: fully-resolved class names
   private java.util.List children = new java.util.ArrayList();
}If you use the import statement, you can save yourself from typing:
import java.util.ArrayList;
import java.util.List;
public class Family
   // NOTE: fully-resolved class names
   private List children = new ArrayList();
}import isn't the same as class loader. It does not bring in any source code at all.
import comes into play when you're compiling or running your code. Java will check to make sure that any "shorthand" class names you give it live in one of the packages you've imported. If it can't find a matching fully-resolved class name, it'll give you a message like "Symbol not found" or something like that.
I arrange Java source in a directory structure that matches the package structure in the .class files.
If I've got a Java source file like this:
package foo.bar;
public class Baz
   public static void main(String [] args)
        Baz baz = new Baz();
        System.out.println(baz);
   public String toString()
       return "I am a Baz";
}I'll store it in a directory structure like this:
root
+---classes
+---src
      +---foo
           +---bar
                +---Baz.javaWhen I compile, I go to root and compile by typing this:
javac -d classes foo/bar/*.javaI can run the code from root by typing:
java -classpath classes foo.bar.BazI hope this wasn't patronizing or beneath you. I don't mean to be insulting. - MOD

Javac(1.4.2) gives error in import statement

Hi All,
I am facing a surprising problem. I have 2 java class files. I write the import statement for second one in the first one. There is no package & these are in the same directory. I have compiled the second one. But when I try to compile the First one. Javac throws error at import statement like below :
D:\Clubs\oct\6>javac -d . ManojTest.java
ManojTest.java:1: '.' expected
import SessionBean;
^
1 error
My Java Files are as below :
import SessionBean;
public class ManojTest
public static void main(String args[])
//ManojTest.java
public class SessionBean
public static void main(String args[])
//SessionBean.java
I have compiled SessionBean.java successfully but when I try to compile ManojTest.java I get error mentioned above.
However this probelm comes when I use j2se 1.4.2.. but works in j2se 1.3.1..
Another way could be I use package structure.
But I can't do any of these, as I have to port my big project to j2se1.4.2.. from j2se1.3.1.. (Live project is running on Tomcat).
Problems is similar in Unix & Windows both.
Is this javac compiler issue or there is some setting which I can make.
I have already included . (dot) in PATH & CLASSPATH environment varibales.
Please help me out if there is any way around this, as i am stuck up in between
thank you
Manoj :confused:

Use a package and then add that package in your classpathOr don't use a package, leave the file in the default (noname) package, and don't use the import statement. Java will find it in the default package without the import.
Explicit import statements from the default package are no longer allowed

How to organize the import statements in FXML Files?

Hello,
I'm a user of NetBeans IDE and it can organize the import statements in *.java files. Now, I'm using JavaFX and editing the *.fxml files as well. I want to know how to organize the import statements in *.fxml files?
Thanks a lot.

You should use Scene Builder, it will make all these import statements for you.
Moreover, it will greatly simplify the writing of your FXML files, since you only have to Drag&Drop JavaFX objects on the scene. Then, it automatically generates FXML files.

NewBee question - Import statements

Hi,
I am new to Bea workshop.
Can someone help me out in how to add my own Import statements in Java classes
created in workshop.
Thanks and Regards,
Nikita

Hi Nikita,
Welcome to Workshop!
The JWS classes used in Workshop are essentially Java classes with the
additional capability to understand the JWS metatags in the comments.
Hence you can use the import statements in the same manner as you use in a
normal Java class.
Please do let us know if you have any further queries.
Regards,
Anurag
Workshop Support
"Nitika" <[email protected]> wrote in message
news:[email protected]..
>
Hi,
I am new to Bea workshop.
Can someone help me out in how to add my own Import statements inJava classes
created in workshop.
Thanks and Regards,
Nikita

Java import statement problems

Hello...
I have the book "Java in a Nutshell, 2nd ed" and have a query about a nested top-level interface example they have in the book.
Basically there's two files/classes. The first, LinkedList.java, is as follows:
public class LinkedList {
    public static interface Linkable {
        // Linkable interface details here
    // rest of LinkedList class here
Next is LinkedList.java as follows:
import LinkedList.*;
class LinkableInteger2 implements Linkable {
    // rest of LinkableInteger2 class here
Now I thought the import statement had two forms - and both used a package name as part of the statement:
import package.class;
import package.*;
Obviously, neither class has a package statement.
As written, these classes do not compile. Am I right in assuming the lack of a package name is causing this problem, or is there something else going on here?
Thanks...
Mark.

Since you don't have package statements in the files, the classes are being placed in the default package. You cannot explicitly import classes from the default package. Al classes in the default package, the java.lang package and the current package are always imported automatically. Your import statement is incorrect - remove it.

Java programming(import statement)

My query is that what if i import whole package instead of one class being used in my code.
eg.
if i need " java.awt.Button" in my program code
and my import statement is
import java.awt.*;
will it be reduce execution performance of my program?
or it will reduce only Complie time performance?

Only the compile time performance. All the import statement does is tells the compiler it can use the classes. Try importing a whole swathe of classes into a small program and see what I mean. The resulting class file doesn't bloat.

Confused about CLASSPATH and how java handles import statements...

Hello,
I must admit I don't get it. I read the articles about setting CLASSPATH etc. but I still wonder:
If you use an import statement, what does the compiler do? I.e. where does it look for the specified classes? I find it confusing because I see in different locations different .jar files:
C:\jdk1.3.1_03\lib\dt.jar
C:\jdk1.3.1_03\lib\htmlconvertor.jar
C:\jdk1.3.1_03\lib\tools.jar
and also
C:\jdk1.3.1_03\jre\lib\i18n.jar
C:\jdk1.3.1_03\jre\lib\rt.jar
C:\jdk1.3.1_03\jre\lib\jaws.jar
C:\jdk1.3.1_03\jre\lib\sunrassign.jar
Can someone explain me what the purpose is of these files?
And why do I have the same contents in
C:\Program Files\JavaSoft\JRE\1.3.1_03\lib
and in
C:\jdk1.3.1_03\jre\lib
Why is that?
Thanks for answering my questions!
-mike

Thanx for the answers, but I still wonder, everyone
here says I need to set the classpath, but I don't.Probably because your classes are already in the class path. The compiler/jvm also look for classes by themselves not just in jar files, when just a directory is supplied in the class path. And a period (".") is a valid directory.
Programs importing different classes compile with no
problem. So what's up with that?
Presumably you are referring to your own code - because they are in the class path.
Second, I still don't understand why the runtime needs
the .jar files. The runtime uses classes, like String, that have to come from somewhere.
This would also mean that end-users
need to set the classpath to the .jar files in their
JRE directory to be able to run programs that import
classes from these .jars. But this is not true, right?No it is true. The end-users will have to set the class path. There are variations on this which make it seem like no class path is set. For instance applets in a browser are java but the end-user does not need to set a class path. That is because the browser knows how to download classes/jars and how to set it up so it uses them. (Actually it uses a class loader, but that is probably more information that you need.)
Because if I make some nice classes myself and import
them, how can I expect my end-user to install these
classes and make a classpath for them?That would be between you and you end-user.
First installation is not part of java. For installation you will have to find something outside of java to accomplish the goal.
Additionally how the class path gets set is OS specific. Java does not deal with that. You will also have to find some way to deal with this (most likely part of the installation.)
There are also variations on this. For example the browser example I gave above. Or using the ext directory. Or creating an executable jar. Or simply setting the class path.
In my understanding it should only be needed in the JDK, not
in the JRE. True or am I mistaken?Mistaken. The class path is needed in the JRE as well. You will need to set it.

Java import statement memory problem

Hi,
will java.io.* loads all the classes in io package to the memory? will it afftect the program performance?

RajBabu wrote:
I hope that import statement might present in a java class fileNo, import statements are in no way represented in the java class files. All references to external classes are made via their fully quallified class names in a class file (com.foo.Bar and not just Bar*).
Imports only serve as a shortcut so that you don't have to write the full class name everywhere in your Source code. You could just as well write a program without using any import statements, just by using the fully qualified class names of each class you use and it would produce the same class files (although the source code would be rather unreadable).
* actually the format is different, but the idea is the same

Import Statement Different ways to refer ???

Dear Friends,
Can any one help me the difference between the usage of import statement....
1. using import statement
2. using the class directly
that is,
for example ;
1. import java.util.Date;
Date dt = new Date();
2. java.util.Date dt = new java.util.Date();
what's the difference between two reference of Date class...is there any meaning beyond this ?????
Regards,
V.Prasanna

what's the difference between two reference of Date
class...is there any meaning beyond this ?????there is no difference once the code is compiled - the compiler resolves single class names to their fully-qualified names (ie with the package prefix) and that appears in the .class file constant pool
before compilation then my opinion is that having all the imports at the top of the file is good practice because you can see what is being used easily

Import Statement Error

Does anyone know what is wrong with these import statement?
import Reduction;
import Mapper;
import ApplyObj;
import ApplyObjUnary;
import java.lang.String;
public class Driver{
public static Driver me = new Driver();
public static void main(String[] args){
int i;
I places all my *.java file in the same directory as Driver.java
But when i try to compile Driver.java, it says :-
C:\assignment1>javac Driver.java
Driver.java:10: '.' expected
import Reduction;
^
Driver.java:11: '.' expected
import Mapper;
^
Driver.java:12: '.' expected
import ApplyObj;
^
Driver.java:13: '.' expected
import ApplyObjUnary;
^
4 errors
I set my class path as
C:\>SET CLASSPATH = .;C:\j2sdk1.4.0_01;c:\assignment1
Apparently, the current directory has been set and my assignment1 directory has been set.
Did i miss out anything? Why does it can't recognize the existence of other class file in the same directory?
thanks.

You don't need to import classes that are in the default package (i.e. you didn't put them in a package). And in Java 1.4, you can't import them. Just remove the import statements, you shouldn't need them.

Import Statement in Java

Similar Messages

Maybe you are looking for