Writing to file in Java - How to Write Full Guide

You already learnt how to read from a file. You will now learn how to write the output of your code to a file.

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Video Transcript

You learned how to read from a file in the earlier examples. Now, what if you want to write to files? Let's say your boss may ask you to read some analytics data from a database, aggregate the data and write it on a spreadsheet. Now you can do this manually, or you can do it more efficiently using your knowledge of programming. For this, you use a feature called File Writer. You also need Try and Catch to catch exceptions that this code may throw in here, you first use Try and Catch for handling any exceptions. Let's create a writer that belongs to the class File Writer. This is used to communicate and write the results in a file. You use Write equals to True to start the writer. Next you take an input from the user and with the help of scan next line, you store it in a string line. Next you write this line in your output file using dot write function. At the end you close the Writer. As a good practice, let's run this code and I'm going to type Mary Had a little Lamp. Now let's go to the file and see if this is what was written in the file. I have my output file and as you can see, Mary Had a Little Lamp was written in my output file which was mentioned in my code here. Now let's print the first thousand prime numbers in a file. The code writes a prime number to the file as soon as it identifies one. First, we are going to create our Writer instance, which will help us write the prime numbers in our output prime text. Next, we write the logic for finding out the prime numbers between two 2000. Once we found the prime number, instead of printing out on the console, we instead write it to our output file. At the end, we simply close the Writer. Let's run this code first. Now let's try and see if output prime text actually has all the prime numbers between two to 1000. So when I open my output prime file, let me zoom in. You can see all the prime numbers from two to thousand have been printed in my output file. In this session you learned about functions. You use some internal functions in Java to save your time. You also learned about exceptions and how to handle them in a code. By now you know how to use conditional statements and loops to implement your logic. And you also know how to use a function to make your task easier.

Video Recap

• File Writer feature in programming can help efficiently write to files

• Try and Catch can handle exceptions thrown in the code

• Creating a Writer instance can write results to a file using the write function

• Input from users can be stored in a string and written to an output file

• Good practice is to run the code to ensure it works

• Logic for finding prime numbers can be written to an output file instead of printing to console

• Functions, conditional statements, and loops can be used to implement logic

• Handling exceptions in code is important

• Using a function can make tasks easier.

In this lecture, you learnt how to write your output to a file. This will make sure that you have your results in a saved format for comparison or in situations when you need to present the output of your code to your clients.