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Easy Learn Java: Programming Articles, Examples and Tips - Page 44


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It is not a big secret that file system in Java looks like UNIX file system. It

Go to all tips in General Java

Question:Java File system looks like UNIX file system. It is understandable since the language was developed by SUN. But what is about the WORA principle "Write once - run everywhere"?

Answer: From the beginning, first versions of Java it was right. I will list most common "beliefs" here and comment them, where

? - "belief"
! - truth

? The file separator may not be /
! Use File.pathSeparator

? The current directory may not be where you expect.
! Ask the user to locate the file with a file dialog.

? Absolute paths may not begin with a file separator.
! Use the getCanonicalPath() method in the File class

? .. may not refer to the parent of the current directory
! use the getParent() method in the File class

? / may not be the root of the file system.
! Use File.listRoots() instead (Java 1.2)

? /tmp and /usr/tmp may not be real files
! Use File.createTempFile() instead (Java 1.2)

? /dev/null may be a real file
! Use a java.io.ByteArrayOutputStream or, better yet, a com.macfaq.io.NullOutputStream

? Copying and moving files often involves more than reading the data in the old location and writing it in the new location.
?! Unfortunatelly it is a true... No good solution in pure Java. You really have to use native code. My opinion is to use System call to OS methods like "cp" in Unix, for example or "copy" in Windows...

Java File system code examples on our site you can find here:

File, FileDescriptorFileFilter, FileInputStream, FilenameFilter,
FileNotFoundException, FileOutputStream, FilePermission, FileReader, FileWriter



69 comments | Printer Friendly Page  Send to a Friend | Score: 4
Posted by jalex on Tuesday, April 22, 2003 (00:00:00) (4212 reads)

Class.forName() loads a JDBC driver into the memory! Why do we need this?

Go to all tips in Databases

Question: Why do we need to use Class.forName() to load a JDBC driver into the memory?

I do not understand idea behind of this...

Answer: Class.forName("MyClass") is used for loading the classes dynamically. JVM executes all its static blocks after class loading.

Everything you need to be initialized put into static block. All JDBC Drivers have a static block that registers itself with DriverManager and DriverManager has static methods only.

By the way, the Class class is only a class in Java that has no public constructor!

 



113 comments | Printer Friendly Page  Send to a Friend | Score: 4
Posted by jalex on Thursday, April 17, 2003 (00:00:00) (15536 reads)

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