Compiling Java with GCJ

 

Before you start, make sure you have a working MinGW environment!

 

How to build a “Hello, world!” example?

HelloWorld.java:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println(“Hello, world!”);
    }
}

Type in the command line:

gcj --main=HelloWorld -o HelloWorld
HelloWorld.java

 

How to build a simple SWT example?

IMPORTANT: libSWT required

HelloSWT.java:

import org.eclipse.swt.widgets.*;

public class HelloSWT {
    public static void main(String[] args) {
        Display display = new Display();
        Shell shell = new Shell(display);
        shell.open();
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch()) {
                display.sleep();
            }
        }
        display.dispose();
    }
}

Type in the command line:

gcj --main=HelloSWT --classpath=swt.jar
-o HelloSWT HelloSWT.java -lswt

 

How to build a simple JNI example?

HelloJNI.java:

public class HelloJNI {
    public native void helloJNI();

    static {
        System.loadLibrary(“helloJNI”);
    }

    public static void main(String[] args) {
        HelloJNI h = new HelloJNI();
        h.helloJNI();
    }
}

helloJNI.c:

#include <jni.h>
#include <stdio.h>
#include “helloJNI.h”

// This method is given by the header file
JNIEXPORT void JNICALL Java_HelloJNI_helloJNI
(JNIEnv *env, jobject obj)
{
    printf(“Hello, world!”);
    return;
}

Type in the command line:

gcj -C HelloJNI.java

gcjh -jni -o helloJNI.h HelloJNI

gcc -shared -o helloJNI.dll helloJNI.c
-Wl,--out-implib,libhelloJNI.a

gcj --main=HelloJNI -fjni -o HelloJNI
HelloJNI.java libhelloJNI.a