Garbage collection and finalize() method

Garbage collection (GC) automatically frees memory occupied by objects that are no longer reachable. The programmer does not need to manually deallocate memory.

When does an object become eligible for GC?

• When there are no references to it.
• When the reference goes out of scope.
• When the reference is reassigned.

Person p = new Person();
p = null;  // object eligible for GC

Requesting garbage collection

You can suggest GC with System.gc() or Runtime.getRuntime().gc(), but the JVM may ignore the request.

finalize() method (deprecated)

The finalize() method was called by the GC before an object is destroyed. It has been deprecated since Java 9 and removed/disabled in later versions because it is unpredictable and causes performance issues.

// Deprecated – do not use
@Override
protected void finalize() throws Throwable {
    // cleanup code (unreliable)
}

Modern alternatives

Use try‑with‑resources, Cleaner, or explicit cleanup methods.

try (FileInputStream fis = new FileInputStream("file.txt")) {
    // automatic resource cleanup
}

Best practices:

• Do not rely on finalize().
• Close resources explicitly.
• Nullify references only if necessary (e.g., large objects).
• Use weak references for caches (WeakHashMap).