Why System.out.println("joint"+3) can work?

When add another object MyObject to a String,it will append MyObject.toString to the String. But for 3(a primary type,int) ,is not an obect ,and have not corresponding toString method.Then how this work?How "joint"+3 to be compiled?

It's magic.
For poorly defined operations (i.e. those not specified in the Java Language Specification Version 2 section 15.18.1.1), the compiler tries to guess what you are trying to do, and then kind of randomly decides what the best guess is and goes with that.

Similar Messages

Why System.out.println() is ok but System.out.print(); ?

why System.out.println() is ok but System.out.print();?
if i leave empty between parantheses in print .compiler gives error but println() doesnt?

gimbal2 wrote:
Think about it for a moment. What would System.out.print() do without any parameters? What CAN it do?That's easy: print() COULD behave like println() without writing a newline at the end ;)
But I agree with Kayaman and Ram: javadoc is very nice, you simply have to read it.

Why System.out.println not PrintStream.println ?

Hi, just a beginner question
I just wonder why should we use System.out.println, not PrintStream.println ?
the field out in the System class is the instance of PrintStream class, isn't it?
So why don't we just use the PrintStream class directly?
Thanks..
Edited by: riff_almighty on Oct 27, 2007 3:27 AM

According to the api:
A PrintStream adds functionality to another output stream, namely the ability to print representations of various data values conveniently. Two other features are provided as well. Unlike other output streams, a PrintStream never throws an IOException; instead, exceptional situations merely set an internal flag that can be tested via the checkError method. Optionally, a PrintStream can be created so as to flush automatically; this means that the flush method is automatically invoked after a byte array is written, one of the println methods is invoked, or a newline character or byte ('\n') is written.
So there is nowhere mentioned about the PrintStream associated with the user console. System.out is the one instance of PrintStream which is associated with the console...
Also println() is not a static method and cant be called upon the class...
Edited by: VijayBabu on Oct 27, 2007 12:51 AM

Why doesn't System.out.println work for Palm?

In my Java code,
how come I don't see any output on my screen (Palm Vx) when I try this?
System.out.println("Hello World");
Where is the output really going to???

Hi,
On POSE (Palm OS emulator), the System.out.println() method output is a file called STDOUT.txt, filed in some directory of the emulator.
On the eal device, I think theres no output for system.out.println().
Ricardo

Why we use logger instead of System.out.println for debugging?

Hi,
why we use logger instead of System.out.println for debugging?
Regard
Sankar

Ya Basha,
good question....
You can use the idoc method to transfer the data when you are having an interface between the sap system and the legacy system......
All the times BDC is not preferable like take the case you developed on upload program with bdc after some days your company thought to go for upgrade the sap vesion from lower version to upper version... in that upgraded version the application may change like sequence of fields or screens at that time you previous bdc program will not work here so u have to develop a new program and and you have to take the things into consideration again...
where as if you use bapi or idoc method it will support the upgradations...
in the case of bdc you have to take the data into flat files.... and then upload it to sap system after all the validations done some times the data which is in the flat file is confidential so there is no security if u take such data in flat file any user can chang the data even though if u maintain the data in application server super user can change the data
where is idoc is fully secured... you can easily establich the interface between the systems and once it is done you can transfer the data with full security because idoc r generated by a program... so there is no manual interaction.....
I think i gave some useful answer to you
~~Guduri

32-bit JDK 7 System.out.println not working in IDE

Hi folks,
I have a 64-bit Windows 7 OS.
Due to 3rd party library/jar dependencies, i had to install the 32-bit Java JDK 1.7 and Eclipse IDE.
I also installed NetBeans.
So i have a 64-bit OS and am running 32-bit Java JDK/JRE & IDEs.
The problem I am having is that my program's System.out.println("...") statements are not outputting strings to either IDE debug console.
Executing the compiled program from a command line/prompt produces the expected string output.
The basic "Hello, World" program is enough to cause this behaviour to start occurring.
I have not manually / intentionally changed any IDE-specific Debug Console or Windows environment settings.
One caveat: This same environment has worked successfully in the past ?! Yes, this is one of those "..it worked last week & yesterday and today it isn't and i swear i didn't do anything..." issue.
Thoughts ?

Thanks for the reply.
The 64-bit versions of Java & Eclipse were installed first.
When i discovered I had to use the 32-bit versions, i un-installed the 64-bit ones & installed the 32-bits.
Even after that initial un-install 64-bit/install 32-bit process, it was working.
I have also been installing the Windows 7 64-bit OS updates when i am informed of them.
I'm not sure if any of these would affect how the Eclipse / NetBeans IDEs behave.
Behaviour has been inconsistent.
Initially it was always working.
But over the past several days, it has been working less and less.
I don't have any large data structures.
This isn't a large complicated program, couple hundred lines, so i highly doubt that i'm doing anything to the resources, but something has changed.
The main project I am working on takes command line parameters, does some initial processing, produces output using System.out.printlns [SOP] then depending on the parameters, branches into 2 different processing paths, let's call them A & B. Each of these processing paths also use SOPs. When i run the program in the IDE going thru path A, sometimes the initial SOP statements will work and the SOP statements specific to path A will also work. If i immediately change the parameters to go thru path B & re-run it, not even the initial SOP statements before the branching decision work.
I've tried doing System.flush()s too - no affect.
I haven't tried the re-direction option to a file option you mentioned yet.
It always works from a command prompt - that is telling me that the Java SOPs are working properly, correct ?
Inside an Eclipse or NetBeans IDE, SOP output to the debug console is inconsistent.
Running from a command prompt, the SOPs always work.
It'd help to know if this an IDE issue, a Java issue, a Windows 7 issue so i can narrow down where to try and correct the situation.
I have a Windows XP VM set up, i'll try running the program there and see if there's a difference.
Thanks for your reply.

System.out.println () is not working properly

Hi, Why does this happens:
Object temp=null;
System.out.println ("temp is null? "+temp==null);
just prints: true
expected: temp is null? true
Why does this happens????
If I do System.out.println ("temp is null? "+(temp==null)); it works bu it should work without the pharentesis too

MelGohan wrote:
Hi, Why does this happens:
Object temp=null;
System.out.println ("temp is null? "+temp==null);
just prints: trueThat is odd, mine prints "false".
type Test126.java
public class Test126 {
    public static void main(String[] args) {
        Object temp=null;
        System.out.println ("temp is null? "+temp);
        System.out.println ("temp is null? "+temp==null);
}javac Test126.java
java Test126
temp is null? null
false

System.out.println not working in Tomcat-4.1.x

System.out.println not working in Tomcat-4.1.24. Any settings has to be enabled??? I am using tomcat for Solaris

I think u can use ServletContext.log() to output info instased.

How does System.out.println(). Work inside src.zip file !

Hello guyz,
I was just wondering how System.out.println() worked so i opened up the src.zip file and checked the source code. But could not understand it. As written i remember
"out is an object encapsulated in the System class."
Thats ok. But i could not understand the code.
    public final static PrintStream out = nullPrintStream();
    private static PrintStream nullPrintStream() throws NullPointerException {
     if (currentTimeMillis() > 0) {
         return null;
     throw new NullPointerException();
    }Also when i ran the DJ Decompiler it decompiled it to this:
public class One
     public static void main(String args[])
          System.out.println("hello world");
import java.io.PrintStream;
public class One
    public One()
    public static void main(String args[])
        System.out.println("hello world");
}Also, why does it need to import PrintStream ?

Peter__Lawrey wrote:
I was just wondering how System.out.println() worked so i opened up the src.zip file and checked the source code.This value is a place holder. This value is changed as soon as enough of the JVM is initialised for printing to work.
Also, why does it need to import PrintStream ? It doesn't, but it is used in the code so DJ is including it just in case.Sorry,
But i don't understand at all.

How can I show a System.out.println(""); into a JSP?

Is a simple doubt that would help me a lot to reach other thing that I wished reach with a JSP.
Thank you!!!

Hi!!!
Thank you to answer me......my question�is because�my problem is a little more complicated��let me tell you�.
My problem is that I wish to do some queries to a table of a Municipalities DB, I have read about that....and according with the exemples....my JSP...should be running and executing very well....but I haven�t had success with that...:(
My JSP file is:
<!doctype html public "-//w3c//dtd html 3.2//en">
<html>

<head>
<title>Query of Municipalities</title>
</head>
<body bgcolor=#FFFFFF>
<font face="Helvetica">
<h1>
<font color=#DB1260>
Municipalities List
</font>
</h1>
<%@ page import="
weblogic.db.jdbc.*,
weblogic.html.*,
java.sql.*
" %>
<p>
<%
Connection conn = null;
try {
Class.forName("weblogic.jdbc.pool.Driver").newInstance();
conn = DriverManager.getConnection("jdbc:weblogic:pool:DESAPool");
catch (Exception e) {
e.printStackTrace();
Statement stmt = conn.createStatement();
stmt.execute("select * from cat_municipio");
ResultSet rs = stmt.getResultSet();
while (rs.next()) {
System.out.println(rs.getInt("cve_municipio") + " - " + rs.getInt("cve_sepomex") + " - " + rs.getString("desc_municipio"));
stmt.close();
conn.close();
%>
<p>Please call Mary with any updates ASAP!
<p>
<font size=-1>Copyright (c) 1999-2000 by BEA Systems, Inc. All Rights Reserved.
</font>
</font>
</body>
</html>
My result obtained is the following:
Municipalities List
Please call Mary with any updates ASAP!
Copyright (c) 1999-2000 by BEA Systems, Inc. All Rights Reserved.
I don�t obtain nothing.....is like DB table were without information......but in reality the DB table has information.....and I can obtain it with the following JSP:
<!doctype html public "-//w3c//dtd html 3.2//en">
<html>

<head>
<title>Query of Municipalities</title>
</head>
<body bgcolor=#FFFFFF>
<font face="Helvetica">
<h1>
<font color=#DB1260>
Municipalities List
</font>
</h1>
<%@ page import="
weblogic.db.jdbc.*,
weblogic.html.*,
java.sql.*
" %>
<p>
<%
Connection conn = null;
try {
Class.forName("weblogic.jdbc.pool.Driver").newInstance();
conn = DriverManager.getConnection("jdbc:weblogic:pool:DESAPool");
// Fetch all records from the database in a TableDataSet
DataSet dSet = new TableDataSet(conn, "cat_municipio").fetchRecords();
TableElement tE = new TableElement(dSet);
tE.setBorder(1);
out.print(tE);
} catch (SQLException sqle) {
out.print("Sorry, the database is not available.");
out.print("Exception: " + sqle);
} catch (Exception e) {
out.print("Exception occured: " + e);
} finally {
if(conn != null)
try {
conn.close();
} catch(SQLException sqle) {}
%>
<p>Please call Mary with any updates ASAP!
<p>
<font size=-1>Copyright (c) 1999-2000 by BEA Systems, Inc. All Rights Reserved.
</font>
</font>
</body>
</html>
and with this JSP I obtain all the following information:
Municipalities List
CVE_MUNICIPIO CVE_SEPOMEX DESC_MUNICIPIO
1 1 ACAJETE
2 2 ACATENO
3 3 ACATLAN
4 4 ACATZINGO
5 5 ACTEOPAN
Now...I need that the first JSP work very well, because...with that way...I can do queries and obtain the needed results for showing them in the Browser......
So, I already find out�.that�any string that I send to the browser with System.out.println(); isn�t showed�.so it is the reason of my question�..how I can see my results of a query using a loop (like a for, while) resolving it....I think my problem would be resolved.
So...I hope you understand me, and you could help me please...thanks.....
Mary
P.D. I also attempted with the following JSP...but the result is the same....I don�t obtain none result...
<!doctype html public "-//w3c//dtd html 3.2//en">
<html>

<head>
<title>Query of Municipalities</title>
</head>
<body bgcolor=#FFFFFF>
<font face="Helvetica">
<h1>
<font color=#DB1260>
Municipalities List
</font>
</h1>
<%@ page import="
weblogic.db.jdbc.*,
weblogic.html.*,
java.sql.*
" %>
<p>
<%
Connection conn = null;
try {
Class.forName("weblogic.jdbc.pool.Driver").newInstance();
conn = DriverManager.getConnection("jdbc:weblogic:pool:DESAPool");
catch (Exception e) {
e.printStackTrace();
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("select CVE_MUNICIPIO, CVE_SEPOMEX, DESC_MUNICIPIO from cat_municipio");
while (rs.next()) {
System.out.println(rs.getInt(1) + " - " + rs.getInt(2) + " - " + rs.getString(3));
rs.close();
stmt.close();
conn.close();
%>
<p>Please call Mary with any updates ASAP!
<p>
<font size=-1>Copyright (c) 1999-2000 by BEA Systems, Inc. All Rights Reserved.
</font>
</font>
</body>
</html>

Want the "System.out.println()" that is within the java stored procedure works?

hello
i write a java stored procedure,and put a line as "System.out.println(...)" within the procedure,after publish it,i can test it within the sqlplus by invoke following command:
SQL>set serveroutput on;
SQL>call dbms_java.set_output(....);
but when i test it within the jdeveloper9.0.3,it can't be print,why?
thank you!

You can try this:
DBMS_OUTPUT.enable(100000);
DBMS_JAVA.set_output(100000);
HTH,
Robert

System.out.println makes things work fine????

I have a case where vector hasto be populated based on some condition. It is in a for loop.But it throws null pointer exception when i try to access the elements in the vector as its empty.So to check that i gave a System.out.println to check the values at the point of inserting the elements into the Vector.At this point it starts working fine.I got this problem 2-3 times.I checked if i missed out something.But that was not the case.A System.out.println was causing the values to be inserted into the vector. I then removed the SoPs and tried.It worked fine.Any Idea??????????this is causing headache for me.I am using eclipse and tomcat4.1 with jdk1.4.2

Honestly roshan, "I checked if i missed out something" and similar just isn't
enough.
You need to post code. Not 1500 lines but a small example that others can
compile and run to observe the behaviour that you observe.
Constructing such an example often helps in solving a problem. If the problem
goes away when you remove code that contains or calls the method in question
that's a sign of where the problem may lie (Even if that code seems to be
irrelevent).
The task of constructing a small example like this is not always easy: but it's
useful for you and essential for others.

Help: What can make "System.out.println" not displaying anything?

Hello,
We have Portal 10g.
I have noticed a pb on the interpretation of existing JSP pages.
I simplified the code... and I noticed that even this command doesn't work :
<%
System.out.println("Hello World");
%>
Any idea ?
Is there any security ? permission I should get ?
JSP works fine on our old 8i environment ...
Thanks in advance for your help.
Olivier

Olivier,
between 8i and 10g are aeons of time (for computer technology). As far as I recall, in 8i came with a Apache and JServ module. This supported Servlets and JSP through a special Oracle implementation. After that OC4J as a J2EE container for EJBs and Servlets/JSPs was introduced.
Using JSPs with the database installation only is not advised anymore. You can use OC4J for that. But be aware that will require some changes in the configuration and deployment of JSPs.
HTH,
--olaf

How can i put a system.out.println into txt file

i want to generate a txt file instead of system.out.println. for the output How can i do that and what code can i use for that??
Edited by: crystalarun on Oct 14, 2007 11:40 AM

suppose u ant output in "Output.txt"
then code can be
PrintStream out = new PrintStream(new FileOutputStream("Output.txt"));
System.setOut(out)

Can't run java apps with System.out.println on any builder.

Hello,
I'm currently using Vista RC2, which is the immediate problem.
Classes with System.out.println won't launch the console window. As I'm a student and practicing on these steps, I do have quite a problem on my hands. I click on run, build succesfull, nothing happens.
I have tried Netbeans and Jcreator, and gave up on trying different builds, as I reckon I'll have to find some other way to counter this; any way to get println messages working in vista?

It is run as a desktop app, and other runs with commands such as JOptionPane do function, only the println windows don't appear at all. So I think JRE is installed and working.
I did notice there was one command for input where I'd be able to enter it at the bottom of Netbeans.
Like just now I clicked build and run for the following code
import java.util.*;
public class FirstProgram
    public static void main(String[] args)
        System.out.println("Hello out there.");
        System.out.println("I will add two numbers for you.");
        System.out.println("Enter two whole numbers on a line:");
        int n1, n2;
        Scanner keyboard = new Scanner(System.in);
        n1=keyboard.nextInt();
        n2=keyboard.nextInt();
        System.out.println("The sum of those two numbers is");
        System.out.println(n1+n2)
}Resulting in a brief flash of "input" in the output window (which is below the coding window) and it dissapears. But this also occurs when I don't include system scanner code.
Using commands in cmd
java -jar "C:\Users\Alegis\Netb\MyApp\dist\MyApp.jar"
Does not yield desired results either. Nothing happens.

Why System.out.println("joint"+3) can work?

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