javaScope errorHard

Static field retention causes application memory leak

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BugFind the bug and fix the code

What it should do

Insert item into cache and return cache size after clearing. Example: manageGlobalCache("session1") -> 0

What happens instead

Static list retains all session objects indefinitely, leaking memory across requests

import java.util.ArrayList;
import java.util.List;

public class Main {
    // Static collection lives for the lifetime of the JVM
    private static final List<String> cache = new ArrayList<>();

    public static int manageGlobalCache(String item) {
        cache.add(item);
        // Forgets to clean up or clear cache after request completion
        return cache.size();
    }

    public static void main(String[] args) {
        System.out.println(manageGlobalCache("session1"));
    }
}

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.

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import java.util.ArrayList; import java.util.List; public class Main { // Static collection lives for the lifetime of the JVM private static final List<String> cache = new ArrayList<>(); public static int manageGlobalCache(String item) { cache.add(item); // Forgets to clean up or clear cache after request completion return cache.size(); } public static void main(String[] args) { System.out.println(manageGlobalCache("session1")); } }

Static field retention causes application memory leak

What it should do

What happens instead

More scope and closure bugs to practise

Static field retention causes application memory leak

What it should do

What happens instead

More scope and closure bugs to practise