Lesson 1
Parsing Table Data in Java
Introduction

Welcome to the first lesson of our course on "Parsing Table Data in Java". In this lesson, we will explore reading and processing table-like data from a text file using Java. This skill is crucial for tasks involving data analysis, generating reports, and various applications requiring structured data manipulation in software development. By the end of this lesson, you'll understand how to parse a 2D table from a file and represent it using Java collections and arrays.

Representing Table Data in Java

Consider a file named students_marks.txt with the following content:

Plain text
15 4 5 5
23 2 3 4
34 4 3 5
43 4 5 4

This file signifies a 2D table where each row denotes a student's scores across four subjects. In Java, you can represent this data using a List of int[] to store each row as an array of integers.

Initialize File Reading

To start, we utilize Files.readAllLines(Paths.get("students_marks.txt")) to read all lines from the file. This method retrieves each line and stores it in a List<String>.

Java
1// Specify the input file path using a Path object
2Path filePath = Paths.get("students_marks.txt");
3
4// Read all lines from the text file
5List<String> lines = Files.readAllLines(filePath);

Here, Files.readAllLines(filePath) opens and reads the file content into a list of strings, with each item representing a line from the file.

Parsing Data into a 2D Structure

Now that we have the lines from the file stored in a List<String>, we'll convert these lines to a usable format, such as a list of integer arrays, by following these steps:

  1. Split each line into tokens: Each line is a string with numbers separated by spaces. We'll split each line string into individual number strings using split(" ").

  2. Convert tokens to integers: After splitting the strings, we'll convert each token into an integer using Integer.parseInt. This transforms the string representations of numbers into integers.

Let's transform each line to an array of integers and then compile these arrays into a list:

Java
1// Initialize a list to store the parsed integer arrays representing each row of data
2List<int[]> data = new ArrayList<>();
3
4// Iterate over each line in the list of lines
5for (String line : lines) {
6    // Split the line by spaces to get string tokens
7    String[] tokens = line.split(" ");
8    // Create an integer array to store parsed numbers from tokens
9    int[] nums = new int[tokens.length];
10    // Convert each token to an integer and store it in the integer array
11    for (int i = 0; i < tokens.length; i++) {
12        nums[i] = Integer.parseInt(tokens[i]);
13    }
14    // Add the integer array representing the row of data to the list
15    data.add(nums);
16}

This code snippet iterates over each line, splits the line into tokens, converts each token to an integer, and stores it in an integer array, which is then added to a list.

Representation of Data

In Java, the students_marks.txt content is stored in a List<int[]>, representing the table as rows and columns:

  • Row indices: Access rows using the list’s index, e.g., data.get(index).
  • Column indices: Access columns within a row using the array index, e.g., data.get(rowIndex)[columnIndex].

The data structure ensures each row corresponds to a line from the file, and each array element corresponds to a number in that line.

Verifying Output

To validate our process, we will print the 2D list structure using Java's standard printing mechanisms.

Java
1// Output the 2D array to verify the result
2System.out.println("Parsed Table Data:");
3for (int[] row : data) {
4    for (int num : row) {
5        System.out.print(num + " ");
6    }
7    System.out.println();
8}

This segment uses nested loops to iterate through each row and print each number in the row space-separated.

Expected Output:

Plain text
15 4 5 5
23 2 3 4
34 4 3 5
43 4 5 4
Summary and Practice Preparation

In this lesson, we explored how to parse table data from a file using Java. We utilized Files.readAllLines for file input and parsed data into a List<int[]> for convenient manipulation. Understanding file input handling and data representation in structured formats like lists and arrays is vital in many practical programming scenarios.

You're now ready to proceed to the practice exercises. These exercises will reinforce your new knowledge by encouraging you to apply similar techniques to other file formats and sizes, enhancing your skills in structured data manipulation in Java. Enjoy the hands-on experience, and see you in the next lesson!

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