Week 7: Enum, Generic Type, Streams, write to file, class diagram/12A. Writing to a File - PrintWriter+++

As the course approaches its end, let's look at a few useful Java techniques and features. 
Some of these have been briefly covered earlier in the course. 
Note, however, that a lot is left out, you will learn more about Java, for example, in the Advanced Object-Oriented Programming course.


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Writing to a File

We've already discussed reading files. 
Let's look at writing to a text file through a few simple examples. 
The program writes the contents of a 'string list' to a file one line at a time.

A line feed character "\n" is added to each line when writing.


First, let's look at a simple example that creates a new file 
and writes a couple of lines of text to it:

try (PrintWriter file = new PrintWriter("test.txt")){
    file.write("Hi everyone!" + "\n");
    file.write("Creating a new file here" + "\n");
    file.write("That's it.");
} 
catch (FileNotFoundException e) {
    System.out.println("An error occurred: " + e);
}
 




As a second example, let's look at a method that takes a LIST of 'String' type and a FILE NAME as parameters. 
The method writes the lines to the file.

First, an example using a for loop:

public static void writeFile(String fileName, ArrayList<String> lines) {
    try (PrintWriter file = new PrintWriter(fileName)){
        for (String line : lines) {
            file.write(line + "\n");
        }
    } catch (FileNotFoundException e) {
        System.out.println("An error occurred: " + e);
    }
}


 


The same example, but utilizing streams:

public static void writeFile(String fileName, ArrayList<String> lines) {
    try (PrintWriter file = new PrintWriter(fileName)){
        lines.stream().forEach(line -> file.write(line + "\n"));
    } 
    catch (FileNotFoundException e) {
        System.out.println("An error occurred: " + e);
    }
}