Question

I have a Java program, and write a makefile to compile it on Linux.

My project organized like this (Run.java is the main entry)

Program - 
   Src - 
       (package)adb.Bing_WebResults
            Run.java
       (package)adb.jsonModel
            *.java
       (package)adb.models
            *.java
   bin - 

   lib - 
       gson.jar
       commons.jar

   resource -
       *.txt

This is my makefile:

# My project require 3 parameters from user input.

default: Run.class
Run.class: src/adb/Bing_WebResults/Run.java
    javac -sourcepath src/ -classpath lib/*.jar -d bin/ src/adb/Bing_WebResults/*.java  src/adb/jsonModels/*.java src/adb/models/*.java


run:
    java -classpath bin/:lib/*.jar  Run  "$(ARG1)" "$(ARG2)" "$(ARG3)"

When I use “make run” command in Linux terminate, exception shows that “Could not find the main class: Run”

Are there something wrong with my makefile? Wrong path or something?

Answer 1

There are many things that could potentially be wrong, but the most apparent issues are the incorrect dependencies of the targets in your makefile.

First of all, the target run should have a dependency on Run.class. If you do make run then make looks at the target called run. In your makefile, this target does not have any dependencies defined, and it will execute the line java ... without checking whether the actual compiled class Run.class exists. As a consequence, if you do make run from a clean situation, your source code will not be compiled and the java command will fail because the compiled class is missing.

Your dependency of default on Run.class is incorrect as well, because Run.class will exist in the bin directory, not in the working directory. The line below mentions the target Run.class as well.

There are several ways to improve your makefile. See below an example of corrected code with some variables added to avoid repeated expressions. This approach is a matter of style and preference though.

BINDIR := bin
RUNCLASS := Run
RUNBINARY := $(BINDIR)/$(RUNCLASS).class
SRCDIR := src/adb/Bing_WebResults
RUNSRC := $(SRCDIR)/$(RUNCLASS).java

# Note: the default target below is superfluous at this moment
default: $(RUNBINARY)
$(RUNBINARY): $(RUNSRC)
        javac -sourcepath src/ -classpath lib/*.jar -d $(BINDIR) $(SRCDIR)/*.java src/adb/jsonModels/*.java src/adb/models/*.java

run: $(RUNBINARY)
        java -classpath $(BINDIR):lib/*.jar  $(RUNCLASS)  "$(ARG1)" "$(ARG2)" "$(ARG3)"

This works for me in a simplified, comparable setup — it might work for you as well. Looking at the snippet you provided, there are most likely other dependencies or changes that need to be added to complete your makefile correctly. Potentially, you might have to add package information to your run command and dependency expressions, but that depends on your source code. Your post does not contain enough information to provide a complete solution.

P.S.: Do not forget to replace spaces by tabs if you copy this code to your own makefile.