Develop Reference

Call a Java class that is in a different Java file than the calling Java class

So, I have a Java file called MinTest.java which contains a call to a class called Min which is located in another file called Min.java. Therefore, the layout is: The MinTest.java method calls the Min class that is in min.java.
I am compiling the code using "javac MinTest.java" but it does not work because it does not recognize Min.
How do I deal with this? I do not want to use an IDE, I need to compile and run everything from the command line. I am using ubuntu.
Thank you.

class Min shall be in Min.java, and to use it in another class Min.class shall be on compilation classpath ( and of course, on execution classpath) - consult javac documentation how to setup it. But to be hones, you can as well do this in IDE. Almost nobody does compile manually. Use ant/maven/gradle/IIDE ofyour choice

Java: Class files containing source code?

I was inspecting the class file format since I wanted to add source code to the class file (which was possible in early Java versions) but all I found was a SourceFile attribute and the SourceDebug attribute. I was looking for the complete source code of the class to be bundled with the class file to ease the post-processing pipeline.
Does anyone know if my memories are wrong or how I can bundle the complete source code of a class within the class file so that I do not have to look up for the java-file when I want to check the source code?
Is there a compiler switch to do that?
Javac has a -g option adding additional debug information. Can someone tell me whats are the information it adds? Without the -g switch it generates lines of code index and source file information.
The main problem I have is generate a class file but only have a reference to a source file that might change. I want simply to bundle up source and class file.
In maven I can simply copy over all the source files to the target directory but would might be incompatible with Eclipse, IntelliJ and NetBeans IDE (and what not)... .

Using a decompiler will also provide a way to extract a useful representation of the source code since most decompiler will value the lines of code information and position the decompiled structures accordingly within the source code.
Since some scenarios will require access to comments and a correct representation on a char by char level, the decompiler would be a second rate solution.

One possible solution I found is defining a new class-file attribute (which is legal) that contains the source. Since the source is huge when compared to the class file, the content might be best compressed (yielding a 1:5 to 1:10 ratio).
This way the class file and the sources stay bundled.
The JVM specification guarantees that every JVM/Tool has to ignore unknown attributes.
I will invest into a wrapper of javac application, that ensures the source was not modified during compilation (and if yes, redo the compilation process) and after compilation is done adding the source code as a class-file attribute.
Since this will be incompatible to the IDE-build cycle of Eclipse (and most likely IntelliJ and NetBeans) it will also require a special post processor.
So integration will also require alternatives to the JavaBuilder.
Once the source code is attached to the class file in question it is very easy to do a lot of advanced stuff with it that helps with both maintaining and managing code. For me its important that the source code and a class stay together and the source information is a 100% percent equal to the source code it was compiled from.

Add a new class to an existing JAR File(which contains source code)

I'll try to illustrate the problem as simple as I can.
I have a JAR file, which I extracted using Winrar. (The jar file contains an open source android library).
I want to modify this JAR file by adding a new class to the library.
So here are my steps:
First, I created a class using Eclipse and set the package name same as the android's library package name.
Second, I copied this java File to the folder of the other java files in the library.
Third, I tried to compile the JAVA file via the CMD using javac.
The path of the new java file and the other .JAVA and .CLASS files of the library is: C:\com\example\core\
The name of the new java file would be: "MyNewClass.java"
The command I run via the CMD is: javac C:\com\example\core\MyNewClass.java
But, during the compilation I get many errors saying: Cannot find symbols.
I've been looking up for a solution of this problem but couldn't figure how to solve it and make the new JAR File having another class that I created seperately.
What am I missing?

As per earlier comments:
Rather than trying to modify the JAR, you can get access to the full source code of the Universal Image Loader library by cloning the repository using git or hitting "Download ZIP" on the righthand side of the page you linked.
Once you have the source, import the library in your IDE. From there on you'll be able to build the whole thing from scratch, make any adjustments/modifications you like, etc.

Your classpath might be wrong or there might be some mistake in package name.
When a Java program is being compiled the compiler it creates a list of all the identifiers in use. If it can't find what an identifier refers to it cannot complete the compilation. This is what the cannot find symbol error message is saying, it doesn't have enough information to piece together what the Java code wants to execute.

Try:
javac -cp com/* C:\com\example\core\MyNewClass.java
That should make the compiler aware of all the other classes under com/...

Why my compiled class has it's methods local variables renamed?

I have a Kitchen.jar file. I need to modify a class inside it. I decompile it with JD. Then I modify the Toster.java file and compile it with:
javac -classpath . Toster.java
And then I take it back into the Kitchen.jar with:
jar -uf Kitchen.jar Toster.class
All works except for one problem. When I open updated Kitchen.jar in JD I see that local variables inside all methods are renamed to something like localLongVar. Why?
The reason I ask is because Kitchen.jar refuses to work after the modification. And I suspect it has to be the compilation problem. Maybe I've misused some flags or anything. Not sure. I have no knowledge of Java whatsoever, except for the basic syntax.
My guess is that I compile it with latest 1.7 version and original jar is compiled with older JDK. That may explain failure of operation, but that doesn't explain the renaming of locals.
EXAMPLE
The random line from the original jar:
BigInteger[] result = new BigInteger[bis.length / 2];
And the very same line of my class:
BigInteger[] arrayOfBigInteger1 = new BigInteger[paramArrayOfBigInteger.length * 2];
So its result vs arrayOfBigInteger1.

By default javac removes debugging information other than source file and line number. Compile with javac -g or javac -g:vars.
From the documentation of javac
-g Generate all debugging information, including local variables. By default, only line number and source file information is generated.
-g:none Do not generate any debugging information.
-g:{keyword list} Generate only some kinds of debugging information, specified by a comma separated list of keywords. Valid keywords are:
source Source file debugging information
lines Line number debugging information
vars Local variable debugging information

The names of the variables are not preserved in compiled code. Most obvious to reduce the size of the compiled class. The compiler will replace them by shorter names. Doing this is also good for obfuscating the code so that someone who decompiles the code has problems to understand the logic. The localLongVar you see in JD is what the compiler makes of the replaced variable names.

How do I use user defined Java classes within Matlab?

I have read the documentation and several websites on exactly how to do this, however Matlab does not seem to pick up the classes that I have added to the dynamic java class path. Nor do I use the right syntax to correctly construct the object.
I have an class HandDB and which to create an object of this type and invoke it's static methods to connect to a SQL database. The class has an empty constructor and takes no parameters. The class is part of a package 'nuffielddb' which I made in a project within Netbeans. All the files are on my usb stick which is my E:\ drive...
I would like to be able to use all the classes within the package. The package is contained at E:\nuffielddb.
I entered the following commands into Matlab:
javaaddpath('E:\');
javaclasspath; % Output from java class path includes E:\ within dynamic path
str = java.lang.String('Test'); % Works fine
db = nuffieldbd.HandDB(); % Does not work - undefined variable or class error
Interesting I typed 'import nuffielddb.*;' and received no error.
Just where am I going wrong?
Thanks for your help btw!

Ah problem solved! Well not solved in a sense! I found out it's actually a problem with my matlab installation and I have no idea how to fix it :-(
Never mind, it works on the computers at the office :-)

if your classes are in a .jar file, make sure your classpath includes the .jar file name itself (not just the directory it's in).
Also if the MATLAB JRE is Java 1.5 (R2006b is, whereas R2009a is Java 1.6, not sure when they switched), make sure your classes are compiled with 1.5 as a target, not 1.6, otherwise MATLAB will not be able to use them.

Minor note: .* imports will never error, so they're not diagnostic. They simply add a package to the list that Matlab searches through when trying to resolve a class name. Nonexistent packages are ignored.
>> import this.package.does.not.exist.*
>>