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

Similar Messages

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.

Import from memory problem

Dear experts:
    When I am using 'import mi[] from memory ID Z_memory.', I don't know how many times can I import from the same memory ID. For example, I want to export once and need to import many times.
    My code is like this:
export mi[] to memory ID Z_memory.
import mi[] from memory ID Z_memory.
import mi[] from memory ID Z_memory.
   Could the second import successful?
   Thanks in advance.
regards,
tyrolu

hi tyrolu,
you can import from the memory for more time also....
why do you want to import same content many times in one program ? instead you can import it at once and you can use it many times right......
sastry

CATS report RCATSP01: Problem with statement IMPORT FROM MEMORY ID.

Hi Guys,
I am trying to create a Z custom report using SAP template RCATSP01. In template report there is an IMPORT statement as below.
IMPORT icatsd
catsfields
fieldtab
FROM MEMORY ID 'LR2'.
When I run the report in debug mode, I found there is no data in ICATSD, CATSFIELDS & FIELDSTAB.
What should I do to get the data in these internal tables.
Thanks,
Mini

I don't think this report is meant to be used as a stand-alone report; it's called within CATS time entry (e.g. CAT2 when user select print time sheet) which would export the info to 'LR2' memory prior to calling this report.

JSP import statement problem

Hey, I got confused with all import statement with jsp.
Here is my problem.
Folder structure:
C:\Program Files\netbeans-4.1\enterprise1\jakarta-tomcat-5.5.7\webapps\ROOT\WEB\S\A
This folder contains a.jsp.
JSP code:
<%@ page
     language="java"
     import="java.sql.*, MyPackage.DataBase"
     errorPage=". . ."
     contentType="text/html; charset=windows-1251"
%>
<%
     Connection connection = null;
     Statement statement = null;
     DataBase dataBase = new DataBase( connection, statement );
%>
...Error message that I get:
org.apache.jasper.JasperException: Unable to compile class for JSP
Generated servlet error:
C:\Program Files\netbeans-4.1\enterprise1\jakarta-tomcat-5.5.7\work\Catalina\localhost\_\org\apache\jsp\WEB\S\A\a_jsp.java:7: package MyPackage does not exist
import MyPackage.DataBase;
                   ^
An error occurred at line: 104 in the jsp file: /WEB/S/A/a.jsp
Generated servlet error:
C:\Program Files\netbeans-4.1\enterprise1\jakarta-tomcat-5.5.7\work\Catalina\localhost\_\org\apache\jsp\WEB\S\A\a100_jsp.java:147: cannot resolve symbol
symbol : class DataBase
location: class org.apache.jsp.WEB.S.A.a_jsp
     DataBase dataBase = new DataBase( connection, statement );
        ^
...How do I import that class so I can use it?
Do I need to use useBean?
What do I need to do?
Thanks

DataBase class does not extend java.sql.
I put this into my jsp page
     import="java.sql.*;"
     import="MyPackage.DataBase;" Here is the error message
Generated servlet error:
C:\Program Files\netbeans-4.1\enterprise1\jakarta-tomcat-5.5.7\work\Catalina\localhost\_\org\apache\jsp\WEB\S\A\a_jsp.java:7: 'class' or 'interface' expected
import MyPackage.DataBase;;
^
1 error
...

Abt "import" statement & Inheritance in Java

Hi, All
As we (Java Programmers) know we'll be using "import java.Math.*" or similar for importing custom/Java packages.
If i have suppose imported "import java.math.BigDecimal;" in a Class 'A' & and iam extending this class 'A' in another class 'B', if i want to use any method from 'BigDecimal' here in this class(i.e., in class 'B') again i need to import "import java.Math.BigDecimal; " .
so, my question is :
1) When we import in one class a package and same package in another class does java import it twice (or) what it does?
2) when I extend a class , why don't this import facility don't get extended.(I think u got my point.)
PS: If any problems in this mail technical or what so ever, iam sorry.
Thanks in advance.

Importation is just a compiler trick. It has nothing to do with runtime.
The separation of sources files brings the necessity of repeated imports from file to file.
You can verify this if you create one source file and put several classes in it: you won't have to import
more than once.
so, my answers are :
1) Each time the compiler encounters an import package.Class statement, it checks the CLASSPATH for the class existence and loads the class definition.
When a reference to the class is done anywhere in the following statements, the compiler checks the referenced entity (member, method...) against the class definition.
2) If the extending class is contained in the same source file, then only one import will be needed.
Hope this helped,
Regards.

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.

A problem from "import" statement

When I was doing some test on "package" and "import" statement, I had a problem.
1 I compiled one class:
package com.sheng.population;
public class A {
     public static int sum (int k, int l) {
          return (k+l);
2 I tried to call the method 'sum' in A:
import com.sheng.population.*;
public class B {
     public static void main(String[] args){
          int i=9;
          int j=100;
          int k = A.sum(i, j);
          System.out.println(k);
Then I got the error message:
"B.java:7: cannot access A
bad class file: E:\newjava\analysis\LDmeasure\A.java
file does not contain class A"
Only after I changed the import statement to "import com.sheng.population.A;" , then it worked.
I just do not know why the '.*' does not work?
Thanks

Let's say your directory structure is "e:\newjava\com\sheng\population\A.class" and "e:\newjava\analysis\LDmeasure\A.java"
If your Classpath is .;e:\newjava and when you compile, your current directory is e:\newjava\analysis\LDmeasure then you have A.java and A.class in your Classpath. When you use "import com.sheng.population.*;" the compiler does not know you mean com.sheng.population.A. The compiler finds A.java and thinks it is the A class that the B class needs. When it tries to compile A.java it finds the class name is com.sheng.population.A which causes the error. When you use "import com.sheng.population.A;" the compiler does not try to use A.java.
If you are keeping the source code in a different directory from the compiled classes, then you should not have the source code in the Classpath. So, if you make sure the current directory is not e:\newjava\analysis\LDmeasure then it should compile.

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.

Program Problems...Import Statement needed?

I am currently a student at DeVry University, and today I had my java class where my professor played a video on java programming for us made by a group called "CBTNuggets". The video went over Inner classes and the professor had us copy the code as the person in the video was typing it up. While attempting to compile the code I encountered several compiler errors on the second of the two files I had typed, I am going to first post the source code for both files, and then follow that with the compiler errors that were generated when I attempted to compile the code. If anyone is able to assist me with this I would greatly appreciate it, I think I may need to add an import statement ;however, I do not know how to implement one for user defined Inner Classes:
Invoice.java was the file that contained the Inner classes
* Invoice.java
* Created on February 1, 2007, 1:39 PM
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
* @author vontux
import java.util.*;
public class Invoice {
    private String strCustName;
    private String strCustAddr;
    private int intInvoiceNum;
    private Date dtInvoiceDate;
    /** Creates a new instance of Invoice */
   Invoice(String sCN, String sCA, int iN, Date dt)
       strCustName = sCN;
       strCustAddr = sCA;
       intInvoiceNum = iN;
       dtInvoiceDate = dt;
class InvoiceItem //enclosed class
      private int intLineItem;
      private int intItemID;
      private int intUnits;
      private String strItemDesc;
      InvoiceItem(int li, int id,String desc, int iu)
          intLineItem = li;
          intItemID = id;
          intUnits = iu;
          strItemDesc = desc;
      public void showInvoice()
          System.out.println("Customer Name: " + Invoice.this.strCustName);
          System.out.println("Item Description: " + strItemDesc);
}UseInvoice.java is the class that is supposed to create objects of the Inner classes from Invoice.java and then run the code:
* UseInvoice.java
* Created on February 1, 2007, 1:51 PM
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
* @author vontux
import java.util.*;
public class UseInvoice {
    public static void main(String[] args)
        Date today = new Date();
        Invoice myInvoice = new Invoice("Robert Barrr", "12345 N. CBTNuggets Dr.", 321,today );
        Invoice.InvoiceItem myInvItem = myInvoice.new InvoiceItem(1, 345,"Toy Train", 2);
        myInvItem.showInvoice();
    /** Creates a new instance of UseInvoice */
    public UseInvoice() {
}And here are the compiler errors that I recieved:
C:\Documents and Settings\Matt\Desktop\temptemp\temp\UseInvoice.java:19: cannot
find symbol
symbol : class Invoice
location: class UseInvoice
        Invoice myInvoice = new Invoice("Robert Barrr", "12345 N. CBTNuggets Dr.
", 321,today );
        ^
C:\Documents and Settings\Matt\Desktop\temptemp\temp\UseInvoice.java:19: cannot
find symbol
symbol : class Invoice
location: class UseInvoice
        Invoice myInvoice = new Invoice("Robert Barrr", "12345 N. CBTNuggets Dr.
", 321,today );
                                ^
C:\Documents and Settings\Matt\Desktop\temptemp\temp\UseInvoice.java:20: package
Invoice does not exist
        Invoice.InvoiceItem myInvItem = myInvoice.new InvoiceItem(1, 345,"Toy Tr
ain", 2);
               ^
3 errors

There are no errors occurs when I compile this two java files .
Here are the result I'm using jdk1.6 and dos command
[output]
[search path for source files: [D:\J2SDK1.6.0\lib, .\out]]
[search path for class files: [D:\J2SDK1.6.0\jre\lib\resources.jar, D:\J2SDK1.6.0\jre\lib\rt.jar, D:\J2SDK1.6.0\jre\lib\sunrsasign.jar, D:\J2SDK1.6.0\jre\lib\jsse.jar, D:\J2SDK1.6.0\jre\lib\jce.jar, D:\J2SDK1.6.0\jre\lib\charsets.jar, D:\J2SDK1.6.0\jre\classes, D:\J2SDK1.6.0\jre\lib\ext\dnsns.jar, D:\J2SDK1.6.0\jre\lib\ext\localedata.jar, D:\J2SDK1.6.0\jre\lib\ext\sunjce_provider.jar, D:\J2SDK1.6.0\jre\lib\ext\sunmscapi.jar, D:\J2SDK1.6.0\jre\lib\ext\sunpkcs11.jar, D:\J2SDK1.6.0\lib, .\out]]
[parsing started .\Invoice.java]
[parsing completed 31ms]
[parsing started .\UseInvoice.java]
[parsing completed 15ms]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Object.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/lang/String.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/util/Date.class)]
[checking Invoice]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/lang/System.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/io/PrintStream.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/io/FilterOutputStream.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/io/OutputStream.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/io/Serializable.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/lang/StringBuilder.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/lang/AbstractStringBuilder.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/lang/CharSequence.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Comparable.class)]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/lang/StringBuffer.class)]
[wrote .\out\Invoice$InvoiceItem.class]
[wrote .\out\Invoice.class]
[checking UseInvoice]
[loading D:\J2SDK1.6.0\lib\ct.sym(META-INF/sym/rt.jar/java/lang/Class.class)]
[wrote .\out\UseInvoice.class]
[total 734ms]
[output]
check your syntax to compile these two files, may be you can show your syntax to compile these two files
javac [options] [classpath] source

Problems with IMPORT STATEMENT

Please, can someone assist me? I am using Java Studio Enterprise 8.1 & Netbeans to design a java application and input form. But the wizard keeps on generating repeated class and subclasses even after I have used the import statement. Its making my program looks clumsy.
I just want to use import statement once and start using the variable in the program without repeating the declaration.
For instance, after importing javax.swing.*, I just want to be able to specify in my program (e.g JPanel Coylogo) without the wizard generating another private javax.swing.JPanel Coylogo.
How can I do it. Please help. I will appreciate
You look at the following section of the program to unstand what I mean. Thank you.
import java.awt.HeadlessException;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.*;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import javax.swing.*;
import java.sql.Date;
* @author */
public class inputForm extends JFrame
private Connection con;
private Statement stmt;
private int k;
ResultSet rs=null;
// Variables declaration - do not modify
private javax.swing.JLabel ClassLabel;
private javax.swing.JPanel Connectivitypanel;
private javax.swing.JPanel Coylogo;
private javax.swing.JCheckBox DataCapable;
private javax.swing.JLabel DateLabel;
// End of variables declaration
* Creates new form inputForm
public inputForm()
//con = new dbConnect();
initComponents();
con = dbconnection();
/** This method is called from within the constructor to
* initialize the form.
* WARNING: Do NOT modify this code. The content of this method is
* always regenerated by the Form Editor.
// <editor-fold defaultstate="collapsed" desc=" Generated Code ">
private void initComponents()
Coylogo = new javax.swing.JPanel();
PhoneType = new javax.swing.JPanel();
PhoneIdLabel = new javax.swing.JLabel();
ClassLabel = new javax.swing.JLabel();
phoneid = new javax.swing.JTextField();
DateLabel = new javax.swing.JLabel();
Connectivitypanel.setBorder(javax.swing.BorderFactory.createTitledBorder("CONNECTIVITY"));
pbluetooth.setText("Bluetooth");
pbluetooth.setActionCommand("bluetooth");
pbluetooth.setBorder(javax.swing.BorderFactory.createEmptyBorder(0, 0, 0, 0));
pbluetooth.setHorizontalAlignment(javax.swing.SwingConstants.TRAILING);
pbluetooth.setHorizontalTextPosition(javax.swing.SwingConstants.LEFT);
pbluetooth.setMargin(new java.awt.Insets(0, 0, 0, 0));
}// </editor-fold>
private void allPhonesTypeActionPerformed(java.awt.event.ActionEvent evt)
}

disable add imports or organize imports in your IDE

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.

Problem in addBatch method in java.sql.Statement Interface

Hi
I am facing a problem java.lang.UnsupportedOperationException when using addbatch() method of java.sql.Statement Interface.
Please suggest solutions.
Thanks
nsgindia

Your JDBC driver doesn't support batch operation, try another driver(not all databases support batch'es eg MySQL)

Weird import statement problem

Hi
I have a strange problem with an application I just developed. Once compiled, if I try to run it on another machine other than the one I developed on, I get a NoClassDefFoundError relating to a class that I did not use. I look at the class file (in a decompiled state) and there is an import statement in there that is not in the source file!! Can anyone tell me why this might have happened?
the import is a symantec class/package I have never used to my knowledge at all and yet it shows up in the binary class file after compilation.
Thanks for any suggestions.

I did use Visual Cafe during parts of the development but I have never imported anything like what is in the class file. I assumed it was VC that was doing it but wasn't sure.
Thanks.

Java import statement memory problem

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