File in Java how to Read and Write File in Java

You can use class in package java.io.* to manage file with java
for example below

Example code for read file line by line with Java

  FileInputStream fs = new FileInputStream("filename.txt"); 
  DataInputStream ds = new DataInputStream(fs);
  BufferedReader br = new BufferedReader(new InputStreamReader(ds));
  String tmp; 
  while ((tmp = br.readLine()) != null)   {
      System.out.println (tmp);
  } 
  ds.close();

Example code for Write file with java
  FileWriter fw = new FileWriter("file_name.txt");
  BufferedWriter out = new BufferedWriter(fw);
  out.write("Test Wrrite1");
  out.write("Test Wrrite2");
  out.write("Test Wrrite3");  
  out.close();