Working with files in java

Question

I have an array of strings. I want to save those strings in a file. The problem is, I need to make a new file called db.txt (only if it doesn't exist), then somehow write strings to it.

And then later I want to be able to read strings from that file and insert them to the array.

Inserting and using array is not the question, but the question is how do I mess with the files? How do I create a new text file (if not existing already), how do I write to it and how do I read from it?

Tried to learn it by myself but I've seen so many ways on the Internet and got confused.

Answer 1

Here is an example of writing to a text file:

File file = new File("./db.txt");
PrintWriter pw = new PrintWriter(file, true); // true for auto-flush
pw.println("Line 1");
pw.println("Line 2");
pw.println("Line 3");
pw.close();

In case you want to append to existing text file:

File file = new File("./db.txt");
FileWriter fw = new FileWriter(file, true); // true for appending
PrintWriter pw = new PrintWriter(fw, true); // true for auto-flush
pw.println("Line 4");
pw.println("Line 5");
pw.println("Line 6");
pw.close();

To read from text file:

File file = new File("./db.txt");
BufferedReader br = new BufferedReader(new FileReader(file));
String line1 = br.readLine();
String line2 = br.readLine();
String line3 = br.readLine();
br.close();

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Also consider the following:

• PrintWriter does not create new file if it does not exist, while FileWriter does.
• To check if a file exists, use: file.exists().
• To check if the file object refers to a file or a directory, use: file.isDirectory() and file.isFile().
• To create a new file, use: file.createNewFile().
• To create a directory, use: file.mkdirs().
• You may need to use the constructors PrintWriter(File file, String csn) and InputStreamReader(InputStream in, Charset cs) to determine the charset.