javaScope errorMedium

Unexpected Resource Behavior in Nested Try-With-Resources

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BugFind the bug and fix the code

What it should do

Read a file and return its content as a string. Example: processFile("example.txt") -> "file content"

What happens instead

java.lang.IllegalStateException: Attempt to set closed stream

import java.io.*;

public class FileProcessor {
    public String processFile(String fileName) {
        String content = "";
        try (FileReader reader = new FileReader(fileName)) {
            try (BufferedReader bufferedReader = new BufferedReader(reader)) {
                content = bufferedReader.readLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return content;
    }
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the scope and closure bugs pattern

Every callback reports the last value, a counter never increments, UnboundLocalError on a variable you can see.

Learn the scope and closure bugs pattern Step through your own code

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import java.io.*; public class FileProcessor { public String processFile(String fileName) { String content = ""; try (FileReader reader = new FileReader(fileName)) { try (BufferedReader bufferedReader = new BufferedReader(reader)) { content = bufferedReader.readLine(); } } catch (IOException e) { e.printStackTrace(); } return content; } }

Unexpected Resource Behavior in Nested Try-With-Resources

What it should do

What happens instead

More scope and closure bugs to practise

Unexpected Resource Behavior in Nested Try-With-Resources

What it should do

What happens instead

More scope and closure bugs to practise