如何检查Vector是否存在并且已经在Java中定义？

Question

I'm attempting to check whether vector.isEmpty() before looping through it but sometimes the vector hasn't even been defined yet because it gets assigned within a function somewhere else. Is there a way to check whether vector == Vector before trying to invoke any Vector methods on said vector?

I'm coming from a JavaScript background and because of its loosely typed system, I can simply do if (isArray(array)) . Is there any similar or standard procedure for checking whether a Vector has been defined before operating on it?

Answer 1

You want:

if(myVector != null) {
    // let's work with it!
}

for this. In Java it must have been declared earlier, eg Vector myVector .

Also, note that Vector is quite an old collection. ArrayList might be the more suitable fit unless you have particular concurrency considerations in play?