Develop Reference

Difference between running with Java & Scala [duplicate]

Can command java run a compiled scala code? If so, why do we have an exclusive command scala?

You can run byte code generated by Scala if you include all necessary runtime libs for Scala (scala-library.jar, scala-swing.jar ...) in the classpath. The scala command does this automatically, and supports Scala specific command line arguments.

Yes, it can. Scala is compiled down to Java bytecode. But remember that it depends on the Scala runtime classes, so you need to still have Scala's jar files on the classpath.
If so, why do we have an exclusive command scala?
Convenience wrapper.

Scala is designed to integrate easily
with applications that run on modern
virtual machines, primarily the Java
virtual machine (JVM). The main Scala
compiler, scalac, generates Java class
files that can be run on the JVM.
-> http://www.artima.com/scalazine/articles/steps.html
As long as you have installed the scala runtime you should be fine: compile classes with scalac and run them with java.

Just want to add my own answer as additional value for the future readers:
scala, if run without parameter, will run an interactive shell
scala, if run with a text file name as parameter, will regard the file as a scala script
those two can't be done using java

If you look closely, the scala command is simply a bash helper-script which summarize to the below command:
$cat /usr/local/Cellar/scala#2.11/2.11.12_1/libexec/bin/scala
execCommand \
"${JAVACMD:=java}" \
$JAVA_OPTS \
"${java_args[#]}" \
"${classpath_args[#]}" \
-Dscala.home="$SCALA_HOME" \
$OVERRIDE_USEJAVACP \
"$EMACS_OPT" \
$WINDOWS_OPT \
scala.tools.nsc.MainGenericRunner "$#"
There are 2 things required to run a .class file compiled using scalac ( the scala compiler) using the java command.
We need to include the scala-library.jar and the location of the .class file in the classpath. To find the location of scala-library.jar, please execute the
below:
which scala /usr/local/opt/scala#2.11/bin/scala
In my case the scala-*.jar files are in :
/usr/local/Cellar/scala#2.11/2.11.12_1/idea/lib on Mac
The location of the Main2.class file which is in /training/example1/scala.
So, to execute the program we could use the below command:
java -cp /usr/local/Cellar/scala#2.11/2.11.12_1/idea/lib/scala-library.jar:/training/example1/scala/ Main2
EDIT-1: If you are using windows, please use semicolon(;) as the separator in java classpath command.

Compiling multiple jar and java files using javac

I downloaded a sample code written in java that has multiple jar files and java files. I am not a Java programmer so I am having a hard time compiling the code. Here's my attempt:
javac -classpath lib/*.jar src/*.java
However this is what I get:
javac: invalid flag: lib/dom4j-1.6.1.jar
Usage: javac <options> <source files>
use -help for a list of possible options
What's wrong with my approach and how can I compile the code? ALl the jar files are located in the lib folder, and the java files in the src folder.

You need to stop the shell from globbing the wild-card in lib/*.jar by escaping it.
Also, you need to remove the .jar suffix ... because that's how classpath wildcards work; see Oracle's "Setting the classpath" document.
So ...
javac -classpath lib/\* src/*.java
Using an IDE is another option. However, if all you want to do is compile and run, then downloading and installing and learning to use an IDE is overkill (IMO). And the flipside is that it is good for an IDE-using Java programmer to also understand how to compile and run from the shell prompt ...

old post, but thought below details help,
you can specify jar files by separating by ; in windows and : in unix
Eg: (windows)
javac -cp first.jar;second.jar;third.jar YourClass.java
(unix)
javac -cp first.jar:second.jar:third.jar YourClass.java
Source: https://gullele.com/pass-all-the-jars-in-classpath-when-compiling-java/

How do I run a Makefile that was distributed with a Java library?

I downloaded a Java library with a file titled Makefile, but I do not know what to run it with. It has no extension, and this is the text that appears when I open it in TextEdit:
all: BigDecimalMath.jar Wigner3jGUI.jar html
html:
javadoc -sourcepath . -private -d html org.nevec.rjm
BigDecimalMath.jar:
javac org/nevec/rjm/*.java
jar cf $# org
Wigner3jGUI.jar:
javac org/nevec/rjm/*.java
jar cmf Wigner3jGUI.mf $# org/nevec/rjm/*.class
distclean:
rm -rf html *.jar org/nevec/rjm/*.class
Could anyone help me figure out how to run this file (By the way, I have a Mac running Mavericks if that matters at all)

try two commands
make
java -jar Wigner3jGUI.jar

Makefiles are similar to ant files and are run by the make program. I have not seen make used to build jars (usually c/c++). However, it looks like it will build the jars. The all target should build the jars, which can then be run by the java command.

Makefile for Java cannot find package

Hello I am new in Java development. I tried to write a makefile which should be runnable in Linux:
JFLAGS = -g
JC = javac
.SUFFIXES: .java .class
.java.class:
$(JC) $(JFLAGS) $*.java
Heap.class: FibonacciHeap.java \
FileOperation.java \
MinLeftistTree.java \
RandomPermutation.java \
Heap.java
default: classes
classes: $(CLASSES:.java=.class)
clean:
$(RM) *.class
In my assumption, Heap.class should be dependent on all the other java file. Also, the main file should be in it as well.
However, I cannot get it run, it shows
Heap.java:3: package heap.FibonacciHeap does not exist
and cannot find the other reference from other java file, such as
Heap.java:61: cannot find symbol symbol : variable RandomPermutation location: class heap.Heap
list = RandomPermutation.GetList(listnum[route]);
This program runs fine in eclipse. Do you have any suggestions?
I am new and I might commit some mistake....and I don't know much about compiler and make file. If you can point it out I will be grateful!

I don't see where you set CLASSPATH. I don't care that it's a make file or Ant - javac.exe and java.exe expect the CLASSPATH to be set when they run. Where's yours?
I believe you have to set CLASSPATH in the makefile, before you run javac.exe.
I'd forget about make (and Eclipse) for a moment. Can you make this project compile and run in a command shell? If you can't, I'd say that you should not be leaning on any tools to help you.
Reading this might be helpful.
Is make really a requirement for fulfilling this assignment? How will the professor know that you used Eclipse or make or Ant or command shell to compile your .java to .class files?

Building Java package (javac to all files)

How to compile all files in directory to *.class files?

Well, this seems pretty obvious, so I may be missing something
javac *.java
(With appropriate library references etc.)
Or perhaps:
javac -d bin *.java
to javac create the right directory structure for the output.
Were you looking for something more sophisticated? If so, could you give more details (and also which platform you're on)?

Yet another way using "find" on UNIX is described here:
http://stas-blogspot.blogspot.com/2010/01/compile-recursively-with-javac.html
The following two commands will compile all .java files contained within the directory ./src and its subdirectories:
find ./src -name *.java > sources_list.txt
javac -classpath "${CLASSPATH}" #sources_list.txt
First, find generates sources_list.txt, a file that contains the paths to the Java source files. Next, javac compiles all these sources using the syntax #sources_list.txt.

Here's a code fragment that I use to build an entire project where, as usual, source files are in a deeply nested hierarchy and there are many .jar files that must go into the classpath (requires UNIX utilities):
CLASSPATH=
for x in $(find | grep jar$); do CLASSPATH="$CLASSPATH:$x"; done
SRC=$(find | grep java$)
javac -cp "$CLASSPATH" $SRC