CODEWITHSUNDEEP
javaeclipse
Joe
Joe

Reputation: 4514

Code works on command line, but not in eclipse (compiling a class from a string...)

So I've got this code that compiles a class from a string and then runs it. It works fine from the command line but not in eclipse... 

import java.lang.reflect.Method;
import java.util.Arrays;
import javax.tools.DiagnosticCollector;
import javax.tools.JavaCompiler;
import javax.tools.JavaCompiler.CompilationTask;
import javax.tools.JavaFileObject;
import javax.tools.ToolProvider;

public class Another2 {

    public static void main(String args[]) throws Exception {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
        String temp = "public class ByeWorld {\n" + "  public static void main(String args[]) {"
                + " System.out.println(\"First of our Compiled Class\");}}";
        JavaFileObject file = new JavaSourceFromString("ByeWorld", temp);
        Iterable<? extends JavaFileObject> compilationUnits = Arrays.asList(file);
        CompilationTask task = compiler.getTask(null, null, diagnostics, null, null, compilationUnits);
        task.call();
        ClassLoader classLoader = Another2.class.getClassLoader();
        Class<?> myclass = classLoader.loadClass("ByeWorld");
        Method mymethod = myclass.getDeclaredMethod("main", new Class[] { String[].class });
        mymethod.invoke(null, new Object[] { null });
    }
}

In the command line I get: 

$ javac Another2.java 
$ java Another2
First of our Compiled Class

But in eclipse I get: 

Exception in thread "main" java.lang.ClassNotFoundException: ByeWorld
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
    at Another2.main(Another2.java:21)

Is something permission-ally going on? is it permanent? And what's my approach for fixing it?

Upvotes: 3

Views: 932

Answers (3)

Subash
Subash

Reputation: 7266

I have had this issues earlier. The way I fixed is simply created a project in Eclipse. Then created all the classes and package with exact same name in eclipse. THen copy and paste the code from your old file to new eclipse class.

Upvotes: 1

Lost In Code
Lost In Code

Reputation: 504

Program worked for me in Eclipse when I added the root project folder as an "external class folder" in the Java Build Path.

For example, let's say my project is located at "C:\EclipseWS\MyProject". Go to Project Properties, then Java Build Path, then to the Libraries tab, and click the "Add External Class Folder" button. Navigate to "C:\EclipseWS\MyProject" then click "OK".

Upvotes: 1

corsiKa
corsiKa

Reputation: 82589

I would bet the directory the file goes in and the directory it's looking to load classes from are different. So essentially it's a working-directory/classpath issue. Remember that Eclipse is trying to make things easier, and it wouldn't expect to look in the current working directory for a .class file.

Try hard-coding where the files should go and be loaded from and see if that changes things. I suspect it will, but can't be sure.

Upvotes: 1

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