编写public static方法q1：判断文件存在及指定子串是否存在

Hey there! Let's work through this problem together to get your q1() method working exactly as you need.

First, let's recap your requirements to make sure we're aligned:

• The method must be public static, take no parameters, and return a boolean.
• It needs to check if the file location.txt exists.
• If the file exists, verify if any line contains the substring "statistical"—return true if found, otherwise false.
• If the file doesn't exist or any IO error pops up, return false.

Complete Implementation Code #

Here's a straightforward, clean version using basic Java IO:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class YourClassName { // Replace with your actual class name
    public static boolean q1() {
        String filename = "location.txt";
        File file = new File(filename);
        
        // Quick check: if file doesn't exist, return false right away
        if (!file.exists()) {
            return false;
        }
        
        // Use try-with-resources to auto-close the scanner (prevents resource leaks)
        try (Scanner scanner = new Scanner(file)) {
            while (scanner.hasNextLine()) {
                String line = scanner.nextLine();
                // Check if current line has the target substring
                if (line.contains("statistical")) {
                    return true; // Found it! No need to check further lines
                }
            }
            // If we exit the loop, no line had the substring
            return false;
        } catch (FileNotFoundException e) {
            // Edge case: file was deleted right after our existence check
            return false;
        }
    }
}

Key Breakdown: #

• File Existence Check: We first create a File object and use file.exists() to immediately return false if the file isn't there.
• Try-with-Resources: The Scanner is wrapped in this block, which automatically closes the scanner once we're done—this is Java best practice to avoid leaving resources open.
• Early Return: As soon as we find a line with "statistical", we return true immediately (no need to waste time checking the rest of the file).
• Exception Safety: Even though we checked the file exists, edge cases (like the file being deleted mid-check) can happen, so we catch FileNotFoundException and return false just in case.

Alternative Modern Version (Java NIO) #

If you prefer a more concise, modern approach using Java NIO streams:

import java.nio.file.Files;
import java.nio.file.Paths;
import java.io.IOException;

public class YourClassName {
    public static boolean q1() {
        String filename = "location.txt";
        
        try {
            // Stream all lines and check if any match our condition
            return Files.lines(Paths.get(filename))
                        .anyMatch(line -> line.contains("statistical"));
        } catch (IOException e) {
            // Covers both "file not found" and other IO errors
            return false;
        }
    }
}

This version uses streams to handle the line check in one line. The IOException will be thrown if the file doesn't exist, so catching it and returning false covers all failure cases.

Either implementation will meet your needs—pick the one that fits better with your codebase's style!

内容的提问来源于stack exchange，提问作者maahi