File Operations In Java

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The “File” class in Java defines many useful methods, here is a program which demonstrates some of these methods.


import java.io.*;public class streams
{public static void main(String []args){File f1=new File("Folder/FILE");File f2=new File("Folder/FILE1");String s;if(f1.exists()){if(f1.isFile()){System.out.println("File Name is "+f1.getName());s=f1.getParent();File f3=new File(s);f1.renameTo(new File("Folder/abc"));f2.delete();if (f3.isDirectory()){System.out.println(f2.getPath());}}else{System.out.println("Not a File");}}}
}
The output of the program is:File Name is FILE
Folder

If successfully run , the ” FILE ” file inside the folder ” Folder ” will be renamed to ” abc ” and the ” FILE1 ” file will be deleted.

Here is an example of a program that reads its own first six bytes, we have:


//0123import java.io.*;public class read
{public static void main(String []args){int s=6;int b[]=new int[6];char c[]=new char[6];try{FileInputStream f = new FileInputStream("read.java");for (int i=0; i&lt;6; i++){b[i] = f.read();c[i] = (char) b[i];}System.out.println("First 6 bytes of the file are :");for (int i=0;i&lt;6;i++)System.out.print(b[i]+" ");System.out.println("nnFirst 6 Bytes as characters  :");for (int i=0;i&lt;6;i++)System.out.print(c[i]);}catch (Exception e){System.out.println("Error");}}
}This program produces the following output:First 6 bytes of the file are :
47 47 48 49 50 51First 6 Bytes as characters are ://0123

Notice that the FileInputStream object is created inside a try-catch block since if the specified-file does not exist, an exception is raised.

In the same way to write data to a file byte-by-byte, we have:


import java.io.*;public class witer
{public static void main(String []args) throws IOException{String s="Hello";byte b[]=s.getBytes();FileOutputStream f=new FileOutputStream("file.txt");int i=0;while(i{f.write(b[i]);i++;}}
}

If the file called file.txt does not exist, it is automatically created.

If we place a true in the constructor for the FileOutputStream, then the file would be opened in append mode.
Note: All file paths used here are relative paths , Use absolute path or add the relative path to the classpath, Copy the folders to the bin folder

转载于:https://my.oschina.net/xiaohelong/blog/497849

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