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Eclipse Setup for ICU4J Users

 Note: This document explains how to build and debug ICU4J 4.4 on Eclipse IDE.  If you plan to contribute code to ICU4J, please also refer following links.


  • Eclipse IDE - Any Eclipse IDE package including the Java IDE.  This instruction uses Eclipse 3.5 on Windows operating system, but other versions of Eclipse should also work.
  • J2SE JRE 5 - Alternatively, you can use JRE 6 for all ICU4J sub-components instead, but you will see some warnings.
  • J2SE JRE 6 - This is required for building ICU4J Locale SPI.

Getting ICU4J Source

The ICU4J source package can be downloaded from the official ICU4 download page.  If you want to work on the latest development snapshot or a specific version of ICU4J, you can directly export the source package from the ICU4J SVN repository.  For accessing the ICU source code repository, please see this page.  This instruction assumes that ICU4J source package is available at C:\icu4j on Windows operating system.  If you have ICU4J source package in a different location or using another operating system, please replace C:\icu4j with the actual location.

Configuring Workspace

The ICU4J source package includes several ICU4J sub-component project files.  These projects refer JRE via Java Execution Environments.  Before importing the ICU4J projects, you must set up Java Execution Environments by following steps.

1. Start Eclipse IDE.  Eclipse will prompt you to select a workspace first time.  This instruction assumes that you create a new workspace for ICU4J.  (Of course, you can use an existing workspace and import ICU4J projects there.)

2. Select [Window] - [Preferences] to open workplace preferences screen.

3. Navigate to Java - Installed JREs - Execution Environments in the tree view in the left pane, then select J2SE-1.5 in the Execution Environments list at the center.

If you do not see any matches in the Compatible JREs list, you have to configure a JRE in the workspace by navigating into Java - Installed JREs, then click Add to register a matching JRE (for this case, JRE 5) installed on your system.

Note: You do not need JREs showing [perfect match] in the list to build ICU4J on Eclipse.  For example, JRE 6 can be used for ICU4J sub-component projects using J2SE-1.5 as the execution environment.  However, Eclipse IDE displays warnings if there is no perfect match.

4. Also make sure the execution environment JavaSE-1.6 has at least one match above.  If no matches, register JRE 6 on your system to the workspace.

Importing ICU4J projects

Once you configure the workspace, the next step is to import ICU4J sub-component project files into the workspace.  This task is done by following steps.

1. Select [File] - [Import] to open the screen below.

Select Existing Projects into Workspace in the screen above, then click Next.

2. Specify C:\icu4j\main as the root directory (If you have the source package in a different directory, replace C:\icu4j with the actual location), then click browse.

You should see ICU4j sub-components projects (icu4j-charset, icu4j-charset-tests...) in Projects list like above.  Click Finish.

3. While importing the projects, you might see the error message below.  But you can just click OK and ignore the message.

4. After the projects are imported into the workplace, you should see the list of projects in the Package Explorer view as below.  (Note: All error indicator icon should be disappeared after Eclipse IDE finishes the import operation.)

5. Build all ICU4J projects by selecting [Project] - [Build All] in the menu.  Now, ICU4J projects imported into the workplace is completely built and ready to work.

6. If you are going to work on sample/demo code, also import the projects under the demos tree parallel to main.

7. If you are going to work on tools, also import the projects under the tools tree parallel to main.

Run the ICU4J Test Suite

After the ICU4J projects are imported and built on the Eclipse IDE, you can run the ICU4J test suite to make sure the ICU4J works properly.  To run the test suite, follow the steps below.

1. In Package Explorer view, open icu4j-test-framework project, then navigate into src - and select

2. Select [Run] - [Run Congigurations...] in the menu to open the screen, then select Java Application in the left pane.  Click New launch configuration icon to create a new configuration for

3. Open Arguments tab and specify -n as Program arguments.

4. Open Classpath tab and select User Entries in the Classpath: list, then click Add Projects... to open the Project Selection screen below.

In this list above, check icu4j-charset, icu4j-charset-tests, icu4j-collate, icu4j-collate-tests, icu4j-core-tests, icu4j-currdata, icu4j-langdata, icu4j-regiondata, icu4j-translit and icu4j-translit-tests, then click OK. (Note: icu4j-core is already included in the classpath because of the build dependency.  Also, ICU4J Locale SPI test suite is not a part of the regular ICU4J test suite.)

5. In the Run Configurations screen, click Run to launch the test suite.  You should see test output in the Console window in the Eclipse IDE.  The test suite usually takes a few minutes.  After all tests are passed, you should see the log like below in the Console window.

Note: On Eclipse Juno (4.2) releases, you may need to run [Project] - [Build All] to let ICU's customer builders to copy data files to appropriate locations. I did not see this issue in Eclipse 3.x and clean projects automatically triggered the desired ICU customer target.


  • JDK is not required for running Eclipse itself.
  • For building ICU4J on Eclipse, you do not need JDK (one exception: icu4j-build-tools project).
  • On Eclipse, we use Eclipse's own Java compiler, not javac in JDK.
  • Although Eclipse has its own Java compiler, it does not have JRE runtime libraries.
  • JRE 5 is the lowest level JRE supported by ICU4J, so we configure ICU4J projects to refer Java runtime library via execution environment J2SE-1.5. (Exception: icu4j-localespi/icu4j-localespi-tests require J2SE-1.6, because Java Locale SPI was introduced in Java 6)
  • JRE 6/7 satisfy the minimum execution environment J2SE-1.5, but contain new APIs not available in JRE 5. If we write code depending on new APIs in Java 6/7, it does not work on JRE 5. Eclipse cannot detect such dependencies, therefore, Eclipse displays the warning. You can ignore the warning for building ICU4J, but I recommend ICU4J developers to install JRE 5 and use it for this purpose.
  • Only icu4j-build-tools project requires JDK, because of JavaDoc library dependency. JavaDoc classes are not a part of Java runtime library (rt.jar).
  • When we build ICU4J release binaries, we use JDK's javac, not Eclipse version. JDK 6 is the current "reference platform", so we use JDK 6 for this purpose, not JDK 5.
For ICU developers, the suggestion is to install:
  • Eclipse 3.5.x (3.6 will be ready soon)
  • JDK 6 (including JRE 6) - this is also used for ant command line build
  • JRE 5 (for execution environment J2SE-1.5)
For non-ICU developers, JRE 5 is optional.