I am trying to compile and run a java program with `CLASSPATH`

& `PATH`

variables with commands as follows:

```
javac -classpath path_to_external_jar:. test.java
java -Djava.library.path=external_lib_folder -classpath path_to_external_jar:. test
```

**test.java code**:

```
package cplextest;
import ilog.concert.*;
import ilog.cplex.*;
import java.io.*;
import java.util.*;
//--------------------------------------------------------------------------
//File: examples/src/QPex1.java
//Version 9.0
//--------------------------------------------------------------------------
//Copyright (C) 2001-2003 by ILOG.
//All Rights Reserved.
//Permission is expressly granted to use this example in the
//course of developing applications that use ILOG products.
//--------------------------------------------------------------------------
//
// Entering and optimizing a QP problem
public class test {
public static void main(String[] args) {
try {
IloCplex cplex = new IloCplex();
IloLPMatrix lp = populateByRow(cplex);
//#ifdef FULLTEST
// cplex.setParam(IloCplex.IntParam.Threads,
// cplex.getMax(IloCplex.IntParam.Threads));
//#endif
if ( cplex.solve() ) {
double[] x = cplex.getValues(lp);
double[] dj = cplex.getReducedCosts(lp);
double[] pi = cplex.getDuals(lp);
double[] slack = cplex.getSlacks(lp);
System.out.println("Solution status = " + cplex.getStatus());
System.out.println("Solution value = " + cplex.getObjValue());
int ncols = lp.getNcols();
for (int j = 0; j < ncols; ++j) {
System.out.println("Column: " + j +
" Value = " + x[j] +
" Reduced cost = " + dj[j]);
}
int nrows = lp.getNrows();
for (int i = 0; i < nrows; ++i) {
System.out.println("Row : " + i +
" Slack = " + slack[i] +
" Pi = " + pi[i]);
}
cplex.exportModel("qpex1.lp");
}
cplex.end();
}
catch (IloException e) {
System.err.println("Concert exception '" + e + "' caught");
}
}
static IloLPMatrix populateByRow(IloMPModeler model) throws IloException {
IloLPMatrix lp = model.addLPMatrix();
double[] lb = {0.0, 0.0, 0.0};
double[] ub = {40.0, Double.MAX_VALUE, Double.MAX_VALUE};
IloNumVar[] x = model.numVarArray(model.columnArray(lp, 3), lb, ub);
double[] lhs = {-Double.MAX_VALUE, -Double.MAX_VALUE};
double[] rhs = {20.0, 30.0};
double[][] val = { {-1.0, 1.0, 1.0},
{ 1.0, -3.0, 1.0} };
int[][] ind = { {0, 1, 2},
{0, 1, 2} };
lp.addRows(lhs, rhs, ind, val);
// Q = 0.5 ( 33*x0*x0 + 22*x1*x1 + 11*x2*x2 - 12*x0*x1 - 23*x1*x2 )
IloNumExpr x00 = model.prod( 33, x[0], x[0]);
IloNumExpr x11 = model.prod( 22, x[1], x[1]);
IloNumExpr x22 = model.prod( 11, x[2], x[2]);
IloNumExpr x01 = model.prod(-12, x[0], x[1]);
IloNumExpr x12 = model.prod(-23, x[1], x[2]);
IloNumExpr Q = model.prod(0.5, model.sum(x00, x11, x22, x01, x12));
double[] objvals = {1.0, 2.0, 3.0};
model.add(model.maximize(model.diff(model.scalProd(x, objvals), Q)));
return (lp);
}
}
```

The `test.java`

is in the current folder. The compilation went through fine but when I run the second command above, the error:`Could not find the main class:test. Program will exit.`

jumps out.

Anyone has advice on this issue?

The problem is with the package your main class is in. Java machine cannot fine your class in default package.

Either remove `package cplextest;`

line from the class or put compiled class into cplextest subfolder and run with command

```
java -classpath path_to_external_jar:. cplextest.test
```