ObjectCollectedException in Java: Understanding this Intricate Exception and Handling it Effortlessly

In this blog post, we’ll dive deep into a specific topic in the realm of Java programming — the ObjectCollectedException. This less talked about but unavoidable exception often pops up on the radar of Java developers, or rather, in their console report. Let’s unravel the nuances of this exception, when and why it occurs, and crucially, how to deal with it effectively.

Unveiling ObjectCollectedException

First off, let’s define what the ObjectCollectedException actually is. It belongs to com.sun.jdi package, a component of Java Debug Interface. This unchecked exception is thrown to indicate a particular object is unreachable because it has been garbage collected.

com.sun.jdi.ObjectCollectedException

This exception often occurs while debugging, when you reference some object, which is already collected by the garbace collector while detaching the debugger. This means, your referenced object no longer exists in the JVM memory space.

Tracing the root

Let’s look at when ObjectCollectedException might occur, with an example that triggers such a situation.

public class Main {
    public void run(int index) {
        String message = "Hello, I'm number " + index;
        if (index != 0) {
            run(index-1);
        }
    }
    public static void main(String[] args) {
        Main test = new Main();
        test.run(10000);
    }
}

Here, the run() method calls itself recursively till the counter index == 0. Because each recursion creates a new String message, several String objects are created. If you try debugging this program by setting a breakpoint inside the run() method and watching the message variable, you’ll likely see ObjectCollectedException as the program creates a large number of objects which the Java Virtual Machine (JVM) garbage collector might decide to clean up.

Decoding the solution

Now that we know when ObjectCollectedException occurs, let’s understand how to tackle it. There is no one-size-fits-all solution, but the approach largely involves proper memory management and handling garbage collection effectively.

For the previous example, we can rewrite it to avoid generating a massive number of String instances by using StringBuilder.

public class Main {
    public void run(int index, StringBuilder message) {
        message.append("Hello, I'm number ").append(index).append('\n');
        if (index != 0) {
            run(index-1, message);
        }
    }
    public static void main(String[] args) {
        Main test = new Main();
        StringBuilder message = new StringBuilder();
        test.run(10000, message);
        System.out.println(message.toString());
    }
}

In addition to the above, here are some tips to avoid the ObjectCollectedException:

1. Avoid Creating Unnecessary Objects: Reuse objects to avoid the creation of unnecessary objects. This allows for better memory management and less work for the garbage collector.

2. Timely Nullification: If an object is no longer needed, explicitly set its reference to null, so that JVM’s garbage collector can reclaim the memory.

3. Use Soft Reference: Alternatively, use of SoftReference objects can instruct the garbage collector about your preference for keeping or deleting the reference.

Here is an example of using SoftReference:

import java.lang.ref.SoftReference;

public class Main {
    public static void main(String[] args) {
        Main obj = new Main();
        SoftReference<Main> sr = new SoftReference<Main>(obj);
        obj = null;
    }
}

In the above code, obj is wrapped around SoftReference. By setting obj = null, the only reference to the Main object is a soft reference. This makes the garbage collector free to collect it depending on the JVM’s memory usage characteristic.

Wrapping Up

ObjectCollectedException is an integral component of Java programming, which deals with objects that vanish before they’re expected to. This exception calls for efficient memory management and effective garbage collection. Using good programming practices such as avoiding unnecessary objects, timely nullification, and SoftReference, this exception can be avoided.

To learn more about ObjectCollectedException in Java or related topics, check out the following resources:

• Java Debug Interface (Oracle official Documentation)
• Garbage Collection in Java (Oracle official Documentation)
• Understanding Java Garbage Collection

Always remember, exception handling is a crucial aspect of any programming and the capacity to avert such scenarios determines proficient coding style. Keep practicing, keep debugging!