See also e45 Deserializing an Object.

				
						Object object = new javax.swing.JButton("push me");
    
    try {
        // Serialize to a file
        ObjectOutput out = new ObjectOutputStream(new FileOutputStream("filename.ser"));
        out.writeObject(object);
        out.close();
    
        // Serialize to a byte array
        ByteArrayOutputStream bos = new ByteArrayOutputStream() ;
        out = new ObjectOutputStream(bos) ;
        out.writeObject(object);
        out.close();
    
        // Get the bytes of the serialized object
        byte[] buf = bos.toByteArray();
    } catch (IOException e) {
    }
				
		

 // Returns the contents of the file in a byte array.

				
						
								    public static byte[] getBytesFromFile(File file) throws IOException {
        InputStream is = new FileInputStream(file);

        // Get the size of the file
        long length = file.length();

        // You cannot create an array using a long type.
        // It needs to be an int type.
        // Before converting to an int type, check
        // to ensure that file is not larger than Integer.MAX_VALUE.
        if (length > Integer.MAX_VALUE) {
            // File is too large
        }

        // Create the byte array to hold the data
        byte[] bytes = new byte[(int)length];

        // Read in the bytes
        int offset = 0;
        int numRead = 0;
        while (offset < bytes.length
               && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
            offset += numRead;
        }

        // Ensure all the bytes have been read in
        if (offset < bytes.length) {
            throw new IOException("Could not completely read file "+file.getName());
        }

        // Close the input stream and return bytes
        is.close();
        return bytes;
    }
								

						
				
		

				
						 File file = new File("filename");
    
    // Get the last modified time
    long modifiedTime = file.lastModified();
    // 0L is returned if the file does not exist
    
    // Set the last modified time
    long newModifiedTime = System.currentTimeMillis();
    boolean success = file.setLastModified(newModifiedTime);
    if (!success) {
        // operation failed.
    }
				
		

				
						    try {
        // Open or create the output file
        FileOutputStream os = new FileOutputStream("outfilename");
        FileDescriptor fd = os.getFD();
    
        // Write some data to the stream
        byte[] data = new byte[]{(byte)0xCA, (byte)0xFE, (byte)0xBA, (byte)0xBE};
        os.write(data);
    
        // Flush the data from the streams and writers into system buffers.
        // The data may or may not be written to disk.
        os.flush();
    
        // Block until the system buffers have been written to disk.
        // After this method returns, the data is guaranteed to have
        // been written to disk.
        fd.sync();
    } catch (IOException e) {
    }
				
		

				
						  // Copies src file to dst file.
    // If the dst file does not exist, it is created
    void copy(File src, File dst) throws IOException {
        InputStream in = new FileInputStream(src);
        OutputStream out = new FileOutputStream(dst);
    
        // Transfer bytes from in to out
        byte[] buf = new byte[1024];
        int len;
        while ((len = in.read(buf)) > 0) {
            out.write(buf, 0, len);
        }
        in.close();
        out.close();
    }
				
		

				
						    File file1 = new File("./filename");
    File file2 = new File("filename");
    
    // Filename paths are not equal
    boolean b = file1.equals(file2);      // false
    
    // Normalize the paths
    try {
        file1 = file1.getCanonicalFile(); // c:\almanac1.4\filename
        file2 = file2.getCanonicalFile(); // c:\almanac1.4\filename
    } catch (IOException e) {
    }
    
    // Filename paths are now equal
    b = file1.equals(file2);              // true
				
		

On Windows, this example creates the path\a\b. On Unix, the path would be /a/b.

				
						    String path = File.separator + "a" + File.separator + "b";
				
		

				
						// Process all files and directories under dir
    public static void visitAllDirsAndFiles(File dir) {
        process(dir);
    
        if (dir.isDirectory()) {
            String[] children = dir.list();
            for (int i=0; i<children.length; i++) {
                visitAllDirsAndFiles(new File(dir, children[i]));
            }
        }
    }
    
    // Process only directories under dir
    public static void visitAllDirs(File dir) {
        if (dir.isDirectory()) {
            process(dir);
    
            String[] children = dir.list();
            for (int i=0; i<children.length; i++) {
                visitAllDirs(new File(dir, children[i]));
            }
        }
    }
    
    // Process only files under dir
    public static void visitAllFiles(File dir) {
        if (dir.isDirectory()) {
            String[] children = dir.list();
            for (int i=0; i<children.length; i++) {
                visitAllFiles(new File(dir, children[i]));
            }
        } else {
            process(dir);
        }
    }
				
		

				
						File dir = new File("directoryName");
    
    String[] children = dir.list();
    if (children == null) {
        // Either dir does not exist or is not a directory
    } else {
        for (int i=0; i<children.length; i++) {
            // Get filename of file or directory
            String filename = children[i];
        }
    }
    
    // It is also possible to filter the list of returned files.
    // This example does not return any files that start with `.'.
    FilenameFilter filter = new FilenameFilter() {
        public boolean accept(File dir, String name) {
            return !name.startsWith(".");
        }
    };
    children = dir.list(filter);
    
    
    // The list of files can also be retrieved as File objects
    File[] files = dir.listFiles();
    
    // This filter only returns directories
    FileFilter fileFilter = new FileFilter() {
        public boolean accept(File file) {
            return file.isDirectory();
        }
    };
    files = dir.listFiles(fileFilter);
				
		

The working directory is the location in the file system from where the java command was invoked.

				
						
								
										
										String curDir = System.getProperty("user.dir");