specification for FileLock.release() says:
"If this lock object is valid then invoking this method releases the lock and renders the object invalid. If this lock object is invalid then invoking this
method has no effect." ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^^^^^^

No effect takes place when release() is called twice, on sparc platform. But for Windows platform it results in IOException.

import java.io.*;
import java.nio.channels.*;
import java.nio.*;

public class Release {

     public static void main(String[] args) throws Exception {
        Release tests = new Release();
        tests.releaseTest01();
     }

    public void releaseTest01() throws Exception {
        RandomAccessFile raf = null;
        FileChannel c = null;
        File tempFile = new File("blahTemp");
        tempFile.deleteOnExit();
        initTestFile(tempFile);
        try {
           raf = new RandomAccessFile(tempFile,"rw");
           c = raf.getChannel();
           FileLock fl1 = c.lock(0,c.size(),true);
           try {
             fl1.release();
             String result = fl1.toString();
             //Check : If this lock object is invalid then invoking this method has no effect.
             fl1.release();
             System.out.println("PASS. Calling release again does not result in anything ");
             if(!(fl1.toString().equals(result))) {
                  System.out.println("FAIL. Calling release again should not result in anything ");
             }
           } catch(Exception e){
              e.printStackTrace();
              System.out.println("FAIL. Calling release again should not result in exception");
           }
        } catch (Exception e) {
           e.printStackTrace();
        }
    }
    private void initTestFile(File blah) throws Exception {
        FileOutputStream fos = new FileOutputStream(blah);
        BufferedWriter awriter
            = new BufferedWriter(new OutputStreamWriter(fos, "8859_1"));
        for(int i=0; i<4000; i++) {
            String number = new Integer(i).toString();
            for (int h=0; h<4-number.length(); h++)
                awriter.write("0");
            awriter.write(""+i);
            awriter.newLine();
        }
       awriter.flush();
       awriter.close();
    }
} // Class Release

For Sparc Machine:
PASS. Calling release again does not result in anything

For Windows NT :
java.io.IOException: The segment is already unlocked
        at sun.nio.ch.FileChannelImpl.release0(Native Method)
        at sun.nio.ch.FileChannelImpl.release(FileChannelImpl.java:514)
        at sun.nio.ch.FileLockImpl.release(FileLockImpl.java:36)
        at Release.releaseTest01(Release.java:26)
        at Release.main(Release.java:9)
FAIL. Calling release again should not result in exception