Using lp_solve 5.5 in Java programs


1. Introduction
2. Installation
3. Usage
4. Implementation notes
5. Building from source
6. Calling lp_solve from Python/Jython

1. Introduction

lp_solve is a free (see LGPL for the GNU lesser general public license) linear (integer) programming solver based on the revised simplex method and the Branch-and-bound method for the integers. lp_solve has its own community via the Yahoo group There you can find the latest sources, executables for the common platforms, examples, manuals and a message board where people can share their thoughts on lp_solve.

lp_solve is written in ANSI C and can be compiled on many different platforms like Linux and Windows. Basically, lp_solve is a library, a set of routines, that can be called easily from programming languages like C, C++, C# and VB. Unfortunately, there is no simple and straightforward way to use native C libraries like lp_solve in Java programs. This library (also called "Java wrapper") is designed to remedy this shortcoming. It consists of two main parts:

This document should help you getting started using the Java wrapper and lp_solve in your Java programs. Read it in addition to the documentation that comes with lp_solve. Always refer to the lp_solve docs as ultimate reference for using the routines of the optimization library. Bug reports, succes stories and requests for changes concerning the Java wrapper are welcome by email at or in the lp_solve discussion group.

The current wrapper version was written to work with lp_solve and was tested under Windows XP and Linux. As long as the API stays the same, other versions of lp_solve are likely to work as well. The wrapper requires a Java Runtime Environment 1.3 or later.

The latest version of the Java wrapper can be found in the files section of the lp_solve group. The wrapper is released under the same LGPL license conditions as lp_solve. A copy of the LGPL text is contained in the distribution archive.

2. Installation

3. Usage

To create a Java application that uses lp_solve routines, you must perform the following steps:

A simple example

The following program is a very simple example that shows how to program with lp_solve in Java.

import lpsolve.*;

public class Demo {

  public static void main(String[] args) {
    try {
      // Create a problem with 4 variables and 0 constraints
      LpSolve solver = LpSolve.makeLp(0, 4);

      // add constraints
      solver.strAddConstraint("3 2 2 1", LpSolve.LE, 4);
      solver.strAddConstraint("0 4 3 1", LpSolve.GE, 3);

      // set objective function
      solver.strSetObjFn("2 3 -2 3");

      // solve the problem

      // print solution
      System.out.println("Value of objective function: " + solver.getObjective());
      double[] var = solver.getPtrVariables();
      for (int i = 0; i < var.length; i++) {
        System.out.println("Value of var[" + i + "] = " + var[i]);

      // delete the problem and free memory
    catch (LpSolveException e) {


Using callbacks

The following code fragment shows you how to use callbacks in Java. The example defines an anonymous inner class that implements the AbortListener interface which is then passed to the putAbortfunc method.

    LpSolve solver = LpSolve.makeLp(0, 4);
    AbortListener abortfunc = new AbortListener() {
      public boolean abortfunc(LpSolve problem, Object handle) {
        System.out.println("Java abortfunc called, handle = " + handle);
        return false;
    solver.putAbortfunc(abortfunc, new Integer(123));

Running the demo application

Follow these steps to run the demo application, which is a port of the C demo program that comes with lp_solve to the Java language. You will need a Java Runtime Environment (JRE) on your machine in order to run the demo. You can download the latest JRE from

More example code

In the demo directory you will find the file which contains more than 100 JUnit test cases (see for details about this highly useful software) to strengthen the faith in the Java wrapper implementation. The test cases may also seve as examples of basic lp_solve usage in Java. You will need the library junit.jar in your CLASSPATH to run the test cases. junit.jar is included in the lib directory of the Java wrapper. You can run the test cases directly by starting the batch script "run_unittests.bat" on Windows or "sh run_unittests" on Linux.

4. Implementation notes

5. Building from source

The Java wrapper archive contains precompiled binary libraries for Windows and Linux. If you just want to use the wrapper there should be no need to build the libs from the sources. But if you absolutely have to, follow the guidelines in this chapter.

On Windows OS

The following prerequisites must be met in order to build the wrapper C library from source on Windows operating systems: Change to the lib/win32 directory and edit the file build.bat. Change the path to the directory where you unpacked the lp_solve Windows archive. Run the script to build lpsolve55j.dll.

On Linux

The following prerequisites must be met in order to build the wrapper C library from source on Linux operating systems: Change to the lib/linux directory and edit the file build. Change the paths to the directory where you unpacked the lp_solve linux archive and where the JDK is installed. Run sh build to build

On Mac OS X

Change to the lib/mac directory and edit the file build_osx. Change the directory paths as indicated in the comments. Thanks to Sean P. Kane ( who provided this build script.

6. Calling lp_solve from Python/Jython

Jython ( is a 100% Java implementation of the popular scripting language Python. One of the most remarkable features of Jython is the seamless interaction between Python and Java. Java programmers can add the Jython libraries to their system to allow end users to write scripts that add functionality to the application. On the other hand, Python/Jython programs can interact with Java packages or with running Java applications.

lp_solve functions can be called via the Java wrapper from Python/Jython programs. See the file in the demo directory of the Java wrapper distribution for an example program. To run this program, you must install lp_solve, the Java wrapper, and Jython. Don't forget to include lpsolve55j.jar in the Java CLASSPATH when you run Jython.