Is there a benefit of assigning an object member variable locally in a method?

Question

In Netty I have seen object member variables assigned locally in class methods quite frequently. Is this a matter of style or is there a programmatic benefit?

I have included a code snippet below:

public ChannelFuture bind() {
    validate();
    SocketAddress localAddress = this.localAddress;
    if (localAddress == null) {
        throw new IllegalStateException("localAddress not set");
    }
    return doBind(localAddress);
}

Notice that `bind()` returns a `ChannelFuture`? I believe that is kept so that a change to the *instance's* `localAddress` doesn't effect the result of the bind call (which might not complete until sometime in the future). — Elliott Frisch, Mar 29 '16 at 20:12

score 2 · Accepted Answer · answered Mar 29 '16 at 20:11

2

I usually see that pattern when multi-threading is a concern. For example, if another thread may alter the member value or null it after the null check, yet it is still a valid use case for member access to occur at that point. Or the code is trying to avoid locks/synchronization. So instead the member is copied to a local and all further operations are done using the local copy to prevent a null access.

answered Mar 29 '16 at 20:11

Robert Baker

71
2

1

Defensive assignment then, makes sense. – MWright Mar 29 '16 at 20:17

Is there a benefit of assigning an object member variable locally in a method?

1 Answers1