I have installed the JDK version 1.6 now the code is compiled but throws a run-time error
class Console1
{
public static void main(String args[])
{
System.console().readLine("this is how we give he input to the string");
System.out.println("this is what we want to print:0)");
}
}
Output
exception in thread "main" java.lang.NoClassDefFoundError: Console
It looks like you are running with a different version of Java. Add this as the first line of code to your "application". It will show the java version which is used to run the application.
System.out.println(System.getProperty("java.version"));
I see this is related to your other thread here.
System.console() returns the Console object, which was added in JDK 1.6, you say you have installed jdk 1.6, so one can only assume that your versions of java you are using to compile and run your code are different.
Can you please tell me what you are using to compile the code, and how you are running the code?
In future, please use the same thread you initially posted, it's much easier for people to trace.
Instead of console you can use...
BufferedReader bufferRead = new BufferedReader(new InputStreamReader(System.in));
String s = bufferRead.readLine();
see example
Related
Summary
1. I am import java.io.console,i am not getting any error in my code,
code is correct, I thought, It's getting some error in eclipse
software... Error :
Exception in thread "main" java.lang.NullPointerException at
loops.Escapey.main(Escapey.java:9)
Coding:
package loops;
import java.io.Console;
public class Escapey {
public static void main(String[] args) {
Console ar = System.console(); // creating a new object for console
String name = ar.readLine("how old are you ?"); //reads a user input
System.out.printf("%s - pretty age",name);
}
}
Ouput :
- I except the output how old are you ?? 18 18 - pretty age
But the actual output is getting error... Exception in thread "main"
java.lang.NullPointerException at loops.Escapey.main(Escapey.java:9)
I assume you are running this into some IDE. Since System.console returns the attached console, if you run it into IDE, it will return NULL. The better approach is to use Scanner class. If you really want to use System.console, you will have to test it on some console. If on Mac, run the terminal. On Linux any of the terminal apps would work.
If we run this in IDE (Intellij), it is throwing null pointer exception. Since this is related to console, I tried to execute this in command line and it works fine.
Execute these steps in terminal or command line and it will work
1) javac Escapey.java
2) java Escapey
Here is the code that's expected to produce error:
public class App {
public static void main (String[] args) {
tick();
}
public static void tick () {
System.out.print("hi");
Note that the closing angled bracket of both, the method tick() and class App is missing. Although the IDE indicates this error while writing code, this compiles and runs just fine. It doesn't look like an issue with Java (or my OS) as doing javac in the command line surely does fail.
What's even funnier...the following code throws a Runtime exception after successfully executing tick():
public class App {
public static void main (String[] args) {
tick();
public static void tick () {
System.out.print("hello..");
Here I skipped closing bracket of main too.
I have installed the development version of Netbeans that has support for Java 9.
[This is a comment more than an answer, but I wanted to include screen shots to show that I cannot reproduce either issue.]
An interesting problem. I just downloaded the most recent nightly build (NetBeans Dev 201803060002) and built your code using Oracle JDK 9.04.
Neither of your code examples would compile for me. For the first example the error for the final line was "reached end of file while parsing System.out.print("hi");". Here is a screen shot:
For the second example, where you removed the closing bracker of main() the additional error reported was "illegal start of expression public static void tick () {":
I suggest that you try the following:
Create a new project and new class "App2" to see if you can replicate the issue with that same version of NetBeans.
If you cannot then review why App compiles and App2 does not.
If you can replicate the problem then download the most recently nightly build to see if you can still replicate the problem (i.e. Invalid source code compiles cleanly). If you cannot then I don't think it is worth raising a bug report or spending further time on the matter.
However, if you can replicate the problem then by all means raise a bug report. But I strongly recommend being able to replicate the failure before doing that. Otherwise you are likely to get a WORKSFORME response if the NetBeans team cannot replicate the issue.
One more thing: it would be helpful to update your OP with the stack trace for that RuntimeException, which you should also include in your bug report.
Ah...I see it now. At some point of time I checked the "Always run without asking" checkbox and since then my IDE is ignoring all the compile time errors without any warnings.
Sorry guys...my bad.
This question already has answers here:
System.console() returns null
(13 answers)
Closed 8 years ago.
I am working on a legacy app which depends on user command line input:
String key = System.console().readLine("Please enter the license key: ");
However, I am getting a NullPointerException because System.console() gives me a null.
Why does System.console() return null for a command line app? It happens when running it out of the terminal as well as IDE.
If you start java from a terminal window, then it really should work, even though I haven't tried on OSX.
If you run a simple test using java directly from the terminal, does it work?
echo 'public class Test { public static void main(String[] args) {System.console().printf("hello world%n");}}' >Test.java && javac Test.java && java Test
Expected output:
hello world
If it doesn't work, then sorry, no console support on your platform.
However, if it works, and your program doesn't then there is a problem with how your program is started.
Check how the java binary started? Is it started from a shell script? Check that stdin/stdout have not been redirected or piped into something, and possibly also that it's not started in the background.
ex: This will probably make System.console() return null.
java Test | tee >app.log
and this:
java Test >/tmp/test.log
This seems to work on my machine (linux)
java Test &
Neither does it seem as if System.setOut, System.setErr or System.setIn affects the console, even after a couple of gc's and finalizers.
However:
Closing (the original) System.out or System.in will disable the console too.
echo 'public class Test { public static void main(String[] args) {System.out.close();System.console().printf("hello world%n");}}' >Test.java && javac Test.java && java Test
Expected output:
Exception in thread "main" java.lang.NullPointerException
at Test.main(Test.java:1)
So; scan your code for places where it closes streams, or passes System.out somewhere it might get closed.
To read from Standard input (command line input) you must use some kind of stream reader to read the System.in stream.
An InputStreamReader initialised by
InputStreamReader(System.in)
lets you read character by character.
However, I suggest wrapping this with a BufferedReader:
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String inputLine = reader.readLine();
Must import
java.io.*;
My DrJava was working fine, but now I keep getting the folowing error whenever I run anything:
Static Error: This class does not have a static void main method accepting String[].
So it will compile OK, but then it shoots out the error . This happens even though everything I test does indeed have a public static void main(String[] args) in it. It seems like a classpath/resources type of error. I appreciate any tips
EDIT: my class
public class Test{
public static void main(String[] args){
System.out.println(" hashmap ");
}
}
There's nothing wrong with the code, so the problem must be with the environment.
Check that you're actually executing that class. Find out where the class that's executed is specified and check it's correct
Check that you're compiling the class. Maybe the code you're looking at has not been compiled and you're trying to execute an old version that was compild before you coded a main()
Check your classpath. Is the compiled class accessible in the classpath of the java command
You don't need to reinstall java, nor is it a java version issue. It may be the way that your are running the program.
To check if it is a problem with your code, do the following:
Make a new folder and put Test.java in it.
Open up Command Line Or Terminal and change to that folder .
Type javac Test.java. Test.class should be in the folder now.
If you want, open up the class with a text editor. This is what I get:
˛∫æ2
<init>()VCodeLineNumberTablemain([Ljava/lang/String;)V
SourceFile Test.java hashmap Testjava/lang/Objectjava/lang/SystemoutLjava/io/PrintStream;java/io/PrintStreamprintln(Ljava/l ang/String;)V! *∑±
% ≤∂±
Back to the command line or terminal, type java Test.
If you get an error, which you shouldn't, I don't know what to say. It should produce the string " hashmap " on to the command line or terminal.
Why re-installing Dr. Java may not work is because you may be using the same working directory, causing same run settings to be used. Dr. Java may be running an external program, one without a main method.
I think that you should install the Eclipse IDE for Java. It is much easier to get around, it looks nicer, and it runs the file or project that you are looking at currently.
Sometimes this problem happens because may be mistake in saving file.you always your file using double quotes and with the .java extension which is main class means that class containing main method.
you should save your file by class name which is public .if there is two classes and both have main method then you should save your file by class name that is public and that class will be run.As like your compiler looking for main method in public static void main(String [] args) that is contract for jvm to run a programme
so it is not able to found that main method that is static and it looking for your Dr class.java
See this Example it have two main methods and practice these kinds of question.I also got this kind of problem in starting.
public class TestFirst
{
public static void main(String [] args){
System.out.println(" TestFirst ");
}
}
class Test{
public static void main(String [] args){
System.out.println(" hashmap ");
}
}
if you save pro-gramme by "TestFirst.java" then o/p will come TestFirst if you do some mistake in main method because we have saved our programme by TestFirst then you will get error like you got.
# 2nd mistake may be this
debian#debian:~/Geany_java$ javac Test1.java
debian#debian:~/Geany_java$ java Test1
Exception in thread "main" java.util.NoSuchElementException
at java.util.StringTokenizer.nextToken(StringTokenizer.java:349)
at Test1.main(Test1.java:11)
your classpath has not set properly See above Compiling successfully but running showing same kind of error you got.Which OS is using I can guide you properly.
Check that actually your file have the .java termination nor the .dj
There is nothing wrong with the code.
It is the executing environment which might have problem. Please share the details.
Check if program compiled correctly.
Check time-stamo of .class file.
Check permissions on folder/directory where class-files are getting generated.
Check if DrJAVA has appropriate permission on the directory.
Did you create a file, compiled it with out main?
Check class-path. Might be possible that previous class file is still being found by JDK in classpath.
Try compiling .java file from cmdLine instead of editor.
As others have mentioned, your code is fine. There must be a problem with your environment. I recently experienced a similar issue when investigating and answering this question.
Basically, in that question, the code Void.class instanceof Class resulted in a compiler error because a user-made Class.class existed in the classpath, so one Class (the Java built-in java.lang.Class) didn't match with the given Class (user-made).
Something similar may be at work here. It is possible that there is a user-made String.class in your classpath. Then in your main signature, String[] args would mean an array of your String, when Dr. Java must be looking for a main method taking an array of the Java built-in String, i.e. java.lang.String[]. If you have a custom String class in your classpath (or in your project?), then the Java compiler will choose it over the built-in String. If you were to compile and run your Test class from the command line, then you would get the runtime error: Exception in thread "main" java.lang.NoSuchMethodError: main.
Following #S0urceC0ded's suggestion, you may find this when looking at Test.class in a text editor:
main([LString;)V // A user-made String class
instead of what it's supposed to be:
main([Ljava/lang/String;)V // The built-in java.lang.String class
If so, remove your own String class (at least the .class file, but also the .java file so the .class file isn't re-created) from the classpath, and compile and run your Test class again.
Without a look at your environment, I can't tell for sure that this is the issue. But it can explain it.
If you are using Dr.Java as IDE, then you need to make sure that the main class containing 'public static void main' should be at the very top of your program. Otherwise Dr.Java throws this error during runtime.
What is the simplest way to call a program from with a piece of Java code? (The program I want to run is aiSee and it can be run from command line or from Windows GUI; and I am on Vista but the code will also be run on Linux systems).
Take a look at Process and Runtime classes. Keep in mind that what you are trying to accomplish is probably not platform independent.
Here is a little piece of code that might be helpful:
public class YourClass
{
public static void main(String args[])
throws Exception
{
Runtime rt = Runtime.getRuntime();
Process proc = rt.exec("name_of_your_application.exe");
int exitVal = proc.exitValue();
System.out.println("Process exitValue: " + exitVal);
}
}
One question in S.O. discussing similiar issues. Another one. And another one.
You can get a runtime instance using Runtime.getRuntime() and call the runtime's exec method, with the command to execute the program as an argument.
For example:
Runtime runTime = Runtime.getRuntime ();
Process proc = rt.exec("iSee.exe");
You can also capture the output of the program by using getting the InputStream from the process.
The difficulty you will run into is how to get the application to know the path. You may want to use an xml or config file, but if you use this link, it should explain how to run a file:
http://www.javacoffeebreak.com/faq/faq0030.html
You may also want to consider passing in some kind of argument to your program to facilitate finding the specific program you want to run.
This could be with command line arguments, properties files or system properties.