How Can I Efficiently Read Specific Lines from a File in Java?

Reading Specific Lines from a File in Java

Retrieving specific lines from a file can be useful in various scenarios. Java offers multiple ways to accomplish this task, particularly when working with both small and large files.

Small Files

If the file size is relatively small, the simplest approach is to read the entire file into memory and then access the desired line. This can be achieved using the Files.readAllLines() method:

String line32 = Files.readAllLines(Paths.get("file.txt")).get(32);

In this example, the Paths.get("file.txt") part represents the file path, and readAllLines() reads the entire file and stores each line as a string in a list. By using get(32), we can directly access the 32nd line from the list.

Large Files

For large files, reading the entire file into memory may be inefficient. In such cases, the Files.lines() method can be used to process the file line by line:

try (Stream<String> lines = Files.lines(Paths.get("file.txt"))) {
    line32 = lines.skip(31).findFirst().get();
}

Here, Files.lines() creates a stream of lines from the file. The skip(31) method skips the first 31 lines, and findFirst() retrieves the 32nd line. Finally, get() converts the optional value to a string.

This approach allows you to efficiently traverse the file and retrieve the desired line without having to load the entire file into memory.

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