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实现�?jdk\bin\native2ascii.exe 同样的功�?转蝲)

zhyiwww — Wed, 12 Jul 2006 04:40:00 GMT

摘要: 实现�?jdk\bin\native2ascii.exe 同样的功�?nbsp; 阅读全文

zhyiwww 2006-07-12 12:40 发表评论

[26] Getting the Size of the Java Memory Heap

zhyiwww — Tue, 13 Jun 2006 05:10:00 GMT

The heap is the area in memory in which objects are created.


// Get current size of heap in bytes
    long heapSize = Runtime.getRuntime().totalMemory();

    // Get maximum size of heap in bytes. The heap cannot grow beyond this size.
    // Any attempt will result in an OutOfMemoryException.
    long heapMaxSize = Runtime.getRuntime().maxMemory();

    // Get amount of free memory within the heap in bytes. This size will increase
    // after garbage collection and decrease as new objects are created.
    long heapFreeSize = Runtime.getRuntime().freeMemory();

zhyiwww 2006-06-13 13:10 发表评论

[25] Computing Elapsed Time

zhyiwww — Tue, 13 Jun 2006 05:07:00 GMT

    // Get current time
    long start = System.currentTimeMillis();

    // Do something ...

    // Get elapsed time in milliseconds
    long elapsedTimeMillis = System.currentTimeMillis()-start;

    // Get elapsed time in seconds
    float elapsedTimeSec = elapsedTimeMillis/1000F;

    // Get elapsed time in minutes
    float elapsedTimeMin = elapsedTimeMillis/(601000F);

    // Get elapsed time in hours
    float elapsedTimeHour = elapsedTimeMillis/(60601000F);

    // Get elapsed time in days
    float elapsedTimeDay = elapsedTimeMillis/(2460601000F);

zhyiwww 2006-06-13 13:07 发表评论

[21] Serializing an Object

zhyiwww — Tue, 13 Jun 2006 04:09:00 GMT

The object to be serialized must implement `java.io.Serializable`. This example serializes a `javax.swing.JButton` 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) {
    }

zhyiwww 2006-06-13 12:09 发表评论

[21] Writing UTF-8 Encoded Data

zhyiwww — Tue, 13 Jun 2006 04:08:00 GMT

    try {
        Writer out = new BufferedWriter(new OutputStreamWriter(
            new FileOutputStream("outfilename"), "UTF8"));
        out.write(aString);
        out.close();
    } catch (UnsupportedEncodingException e) {
    } catch (IOException e) {
    }

zhyiwww 2006-06-13 12:08 发表评论

[20] Reading UTF-8 Encoded Data

zhyiwww — Tue, 13 Jun 2006 04:07:00 GMT

    try {
        BufferedReader in = new BufferedReader(
            new InputStreamReader(new FileInputStream("infilename"), "UTF8"));
        String str = in.readLine();
    } catch (UnsupportedEncodingException e) {
    } catch (IOException e) {
    }

zhyiwww 2006-06-13 12:07 发表评论

[19] Using a Random Access File

zhyiwww — Tue, 13 Jun 2006 04:06:00 GMT

    try {
        File f = new File("filename");
        RandomAccessFile raf = new RandomAccessFile(f, "rw");

        // Read a character
        char ch = raf.readChar();

        // Seek to end of file
        raf.seek(f.length());

        // Append to the end
        raf.writeChars("aString");
        raf.close();
    } catch (IOException e) {
    }

zhyiwww 2006-06-13 12:06 发表评论

[17] Reading a File into a Byte Array

zhyiwww — Tue, 13 Jun 2006 04:05:00 GMT

This example implements a method that reads the entire contents of a file into a byte array.

// 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;
    }

zhyiwww 2006-06-13 12:05 发表评论

[14] Reading Text from Standard Input

zhyiwww — Tue, 13 Jun 2006 04:03:00 GMT

    try {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        String str = "";
        while (str != null) {
            System.out.print("> prompt ");
            str = in.readLine();
            process(str);
        }
    } catch (IOException e) {
    }

zhyiwww 2006-06-13 12:03 发表评论

[12] Getting and Setting the Modification Time of a File or Directory

zhyiwww — Tue, 13 Jun 2006 04:02:00 GMT

This example gets the last modified time of a file or directory and then sets it to the current time.

				
						 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.
    }

zhyiwww 2006-06-13 12:02 发表评论

[11] Forcing Updates to a File to the Disk

zhyiwww — Tue, 13 Jun 2006 04:01:00 GMT

In some applications, such as transaction processing, it is necessary to ensure that an update has been made to the disk. `FileDescriptor.sync()` blocks until all changes to a file are written to disk.

				
						    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) {
    }

zhyiwww 2006-06-13 12:01 发表评论

[10] Creating a Temporary File

zhyiwww — Tue, 13 Jun 2006 04:00:00 GMT

    try {
        // Create temp file.
        File temp = File.createTempFile("pattern", ".suffix");

        // Delete temp file when program exits.
        temp.deleteOnExit();

        // Write to temp file
        BufferedWriter out = new BufferedWriter(new FileWriter(temp));
        out.write("aString");
        out.close();
    } catch (IOException e) {
    }

zhyiwww 2006-06-13 12:00 发表评论

[9] Copying One File to Another

zhyiwww — Tue, 13 Jun 2006 03:58:00 GMT

This example uses file streams to copy the contents of one file to another file. See e172 Copying One File to Another for an example that uses file channels.

				
						  // 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();
    }

zhyiwww 2006-06-13 11:58 发表评论

[8] Determining If Two Filename Paths Refer to the Same File

zhyiwww — Tue, 13 Jun 2006 03:56:00 GMT

A filename path may include redundant names such as ``.`' or ``..`' or symbolic links (on UNIX platforms). `File.getCanonicalFile()` converts a filename path to a unique canonical form suitable for comparisons.

				
						    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

zhyiwww 2006-06-13 11:56 发表评论

[7] Getting an Absolute Filename Path from a Relative Filename Path

zhyiwww — Tue, 13 Jun 2006 03:55:00 GMT

    File file = new File("filename.txt");
    file = file.getAbsoluteFile(); // c:\temp\filename.txt

    file = new File("dir"+File.separatorChar+"filename.txt");
    file = file.getAbsoluteFile(); // c:\temp\dir\filename.txt

    file = new File(".."+File.separatorChar+"filename.txt");
    file = file.getAbsoluteFile(); // c:\temp\..\filename.txt

    // Note that filename.txt does not need to exist

zhyiwww 2006-06-13 11:55 发表评论

[6] Converting Between a Filename Path and a URL

zhyiwww — Tue, 13 Jun 2006 03:53:00 GMT

    // Create a file object
    File file = new File("filename");

    // Convert the file object to a URL
    URL url = null;
    try {
        // The file need not exist. It is made into an absolute path
        // by prefixing the current working directory
        url = file.toURL();          // file:/d:/almanac1.4/java.io/filename
    } catch (MalformedURLException e) {
    }

    // Convert the URL to a file object
    file = new File(url.getFile()); // d:/almanac1.4/java.io/filename

    // Read the file contents using the URL
    try {
        // Open an input stream
        InputStream is = url.openStream();

        // Read from is

        is.close();
    } catch (IOException e) {
        // Could not open the file
    }

zhyiwww 2006-06-13 11:53 发表评论

[5] Constructing a Filename Path

zhyiwww — Tue, 13 Jun 2006 03:52:00 GMT

A `File` object is used to represent a filename. Creating the `File` object has no effect on the file system; the filename need not exist nor is it created.

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";

zhyiwww 2006-06-13 11:52 发表评论

[4] Traversing the Files and Directories Under a Directory

zhyiwww — Tue, 13 Jun 2006 03:49:00 GMT

This example implements methods that recursively visits all files and directories under a directory.

				
						// 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; iprocess(dir);
    
            String[] children = dir.list();
            for (int i=0; iprocess(dir);
        }
    }

zhyiwww 2006-06-13 11:49 发表评论

[3] Listing the Files or Subdirectories in a Directory

zhyiwww — Tue, 13 Jun 2006 03:45:00 GMT

This example lists the files and subdirectories in a directory. To list all descendant files and subdirectories under a directory, see e33 Traversing the Files and Directories Under a Directory .

				
						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

zhyiwww 2006-06-13 11:45 发表评论

[2] Getting the Current Working Directory

zhyiwww — Tue, 13 Jun 2006 03:43:00 GMT

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

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

zhyiwww 2006-06-13 11:43 发表评论

[1] Copying a Directory

zhyiwww — Tue, 13 Jun 2006 03:37:00 GMT

    // Copies all files under srcDir to dstDir.
    // If dstDir does not exist, it will be created.
    public void copyDirectory(File srcDir, File dstDir) throws IOException {
        if (srcDir.isDirectory()) {
            if (!dstDir.exists()) {
                dstDir.mkdir();
            }

            String[] children = srcDir.list();
            for (int i=0; i                copyDirectory(new File(srcDir, children[i]),
                                     new File(dstDir, children[i]));
            }
        } else {
            // This method is implemented in e1071 Copying a File
            copyFile(srcDir, dstDir);
        }
    }

zhyiwww 2006-06-13 11:37 发表评论

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实现�?jdk\bin\native2ascii.exe 同样的功�?转蝲)

[26] Getting the Size of the Java Memory Heap

[25] Computing Elapsed Time

[21] Serializing an Object

The object to be serialized must implement java.io.Serializable. This example serializes a javax.swing.JButton object.

[21] Writing UTF-8 Encoded Data

try { Writer out = new BufferedWriter(new OutputStreamWriter( new FileOutputStream("outfilename"), "UTF8")); out.write(aString); out.close(); } catch (UnsupportedEncodingException e) { } catch (IOException e) { }

[20] Reading UTF-8 Encoded Data

try { BufferedReader in = new BufferedReader( new InputStreamReader(new FileInputStream("infilename"), "UTF8")); String str = in.readLine(); } catch (UnsupportedEncodingException e) { } catch (IOException e) { }

[19] Using a Random Access File

try { File f = new File("filename"); RandomAccessFile raf = new RandomAccessFile(f, "rw"); // Read a character char ch = raf.readChar(); // Seek to end of file raf.seek(f.length()); // Append to the end raf.writeChars("aString"); raf.close(); } catch (IOException e) { }

[17] Reading a File into a Byte Array

This example implements a method that reads the entire contents of a file into a byte array.

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

[14] Reading Text from Standard Input

try { BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); String str = ""; while (str != null) { System.out.print("> prompt "); str = in.readLine(); process(str); } } catch (IOException e) { }

[12] Getting and Setting the Modification Time of a File or Directory

This example gets the last modified time of a file or directory and then sets it to the current time.

[11] Forcing Updates to a File to the Disk

In some applications, such as transaction processing, it is necessary to ensure that an update has been made to the disk. FileDescriptor.sync() blocks until all changes to a file are written to disk.

[10] Creating a Temporary File

try { // Create temp file. File temp = File.createTempFile("pattern", ".suffix"); // Delete temp file when program exits. temp.deleteOnExit(); // Write to temp file BufferedWriter out = new BufferedWriter(new FileWriter(temp)); out.write("aString"); out.close(); } catch (IOException e) { }

[9] Copying One File to Another

This example uses file streams to copy the contents of one file to another file. See e172 Copying One File to Another for an example that uses file channels.

[8] Determining If Two Filename Paths Refer to the Same File

A filename path may include redundant names such as `.' or `..' or symbolic links (on UNIX platforms). File.getCanonicalFile() converts a filename path to a unique canonical form suitable for comparisons.

[7] Getting an Absolute Filename Path from a Relative Filename Path

[6] Converting Between a Filename Path and a URL

[5] Constructing a Filename Path

A File object is used to represent a filename. Creating the File object has no effect on the file system; the filename need not exist nor is it created.

[4] Traversing the Files and Directories Under a Directory

This example implements methods that recursively visits all files and directories under a directory.

[3] Listing the Files or Subdirectories in a Directory

This example lists the files and subdirectories in a directory. To list all descendant files and subdirectories under a directory, see e33 Traversing the Files and Directories Under a Directory .

[2] Getting the Current Working Directory

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

[1] Copying a Directory

The object to be serialized must implement `java.io.Serializable`. This example serializes a `javax.swing.JButton` object.

try {
Writer out = new BufferedWriter(new OutputStreamWriter(
new FileOutputStream("outfilename"), "UTF8"));
out.write(aString);
out.close();
} catch (UnsupportedEncodingException e) {
} catch (IOException e) {
}

try {
BufferedReader in = new BufferedReader(
new InputStreamReader(new FileInputStream("infilename"), "UTF8"));
String str = in.readLine();
} catch (UnsupportedEncodingException e) {
} catch (IOException e) {
}

try {
File f = new File("filename");
RandomAccessFile raf = new RandomAccessFile(f, "rw");

// Read a character
char ch = raf.readChar();

// Seek to end of file
raf.seek(f.length());

// Append to the end
raf.writeChars("aString");
raf.close();
} catch (IOException e) {
}

try {
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String str = "";
while (str != null) {
System.out.print("> prompt ");
str = in.readLine();
process(str);
}
} catch (IOException e) {
}

In some applications, such as transaction processing, it is necessary to ensure that an update has been made to the disk. `FileDescriptor.sync()` blocks until all changes to a file are written to disk.

try {
// Create temp file.
File temp = File.createTempFile("pattern", ".suffix");

// Delete temp file when program exits.
temp.deleteOnExit();

// Write to temp file
BufferedWriter out = new BufferedWriter(new FileWriter(temp));
out.write("aString");
out.close();
} catch (IOException e) {
}

A filename path may include redundant names such as ``.`' or ``..`' or symbolic links (on UNIX platforms). `File.getCanonicalFile()` converts a filename path to a unique canonical form suitable for comparisons.

A `File` object is used to represent a filename. Creating the `File` object has no effect on the file system; the filename need not exist nor is it created.

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