Creating a dangling pointer using Java

Question

How can i create a dangling pointer using Java?

Answer 1

It depends on your definition of dangling pointer.

If you take the Wikipedia definition of a dangling pointer, then no, you can't have it in Java. Because the language is garbage collected, the reference will always point to a valid object, unless you explicitly assign 'null' to the reference.

However, you could consider a more semantic version of dangling pointer. 'Semantic dangling reference' if you will. Using this definition, you have a reference to a physically valid object, but semantically the object is no longer valid.

String source = "my string";
String copy = source;

if (true == true) {
    // Invalidate the data, because why not
    source = null;
    // We forgot to set 'copy' to null!
}

// Only print data if it hasn't been invalidated
if (copy) {
    System.out.println("Result: " + copy)
}

In this example, 'copy' is a physically valid object reference, yet semantically it is a dangling reference, since we wanted to set it to null, but forgot. The result is that code that uses 'copy' variable will execute with no problems, even though we meant to invalidate it.