Java Package Execution

Question

Here's my Situation: I have a folder Structure:

C:\Users\user\Desktop\JavaTraining\Chapter3\examples.

examples is also a folder. Now, I have a file name Calculator.Java in Chapter3 folder with the package statement package Chapter3;. So, from the Command Line I compiled the file from the JavaTraining directory as javac Chapter3\Calculator.java, It compiled and I see a file Calculator.class generated. But when I run the command java Chapter3.Calculator from the JavaTraining Directory. It throwed me an error: Could not find file or load main class Chapter3.Calculator.

Then, I created a sub folder in Chapter3 named examples and copied the Calculator.java into the examples folder and tried compiling and executing the file thinking Chapter3 as the root folder ( executed commands from the Chapter3 directory). No error, the file got executed.

Please can anyone explain me why this happened or what is the reason behind it, I am going mad...

Calculator.java is just a class Calculator with main function trying to find a sum from a printsum function of two variables.

I went through the suggestions provided in http://stackoverflow.com/questions/18093928/what-does-could-not-find-or-load-main-class-mean According to the above, it was either the syntax mistake ( the way of trying to executing the file) or setting the PATH and CLASSPATH environment variables.

I even tried the echo %CLASSPATH% to see if my CLASSPATH variable is set to current directory. It did show me the . when I executed the echo command from JavaTraining directory. The file did not execute when I tried Chapter3 folder as root directory, but when I create a subfolder in Chapter3 and made Chapter3 as the root directory, it executed, what might be the reason or what am I doing wrong,

Here is the command line with the output:

C:\Users\vikas\Desktop\JavaTraining>javac Chapter3\Calculator.java

C:\Users\vikas\Desktop\JavaTraining>java Chapter3.Calculator
Error: Could not find or load main class Chapter3.Calculator

C:\Users\vikas\Desktop\JavaTraining>cd Chapter3

C:\Users\vikas\Desktop\JavaTraining\Chapter3>javac examples\Calculator.java

C:\Users\vikas\Desktop\JavaTraining\Chapter3>java examples.Calculator
The sum is 30

C:\Users\vikas\Desktop\JavaTraining\Chapter3>

The Calculator.java file:

// One Package Statement
package chapter3;
// The file in Chapter 3 folder, file in example folder has
//package examples;
// One or more import statements
import java.io.*;
import java.util.*;

// Class Declaration
public class Calculator {

    // State. Variables and Constants
    int i=10;
    long k = 20;

    // Behavior, one or more methods
     void printSum(){
         long sum;
         sum = i+ k;
    System.out.println("The sum is " + (i+k));
    }
    public static void main (String[] args) {
    Calculator c = new Calculator();
    c.printSum();
    }
}

The classpath has to be set to the top of the package hierarchy. If it's set to . then you should invoke java from there or set a classpath with the flag cp — pvg
– pvg, Commented Mar 21, 2017 at 13:18
from package JavaTraining, should be able to do both: javac Chapter3\Calculator.java and java Chapter3\Calculator — LeTex
– LeTex, Commented Mar 21, 2017 at 13:22
@pvg: the classpath is set to ' . ', can you please elaborate on what you mean — user2534033
– user2534033, Commented Mar 21, 2017 at 13:49

matt · Accepted Answer · 2017-03-21 13:17:46Z

1

When you build a file, it is good to have a build directory, then java will put the class in the correct package layout.

mkdir build
javac -d build path/to/source/Files.java
java -cp build package.name.Files

answered Mar 21, 2017 at 13:17

matt

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