How to measure the performance speed of one method in java

Question

I have implemented a protocol and it is executed and give me the output I want but the problem is the runtime execution. Is a little more than I would expected. I wanted to measure the execution time of one of my methods of the class but I am not sure if what I have done is correct since I do not have much experience in testing.
What I have done is:

public class MyClass {
    // some private fields here

    public int method toBeMeasured (int a){
        long startTime=System.nanoTime();

        // the code under my method including 
        // some for cycles and some operation.

        long finalTime=System.nanoTime() - startTime;

        return something of type int;
    }
}

Now what I need to know if the result I got is really telling me the performance speed of this method or am I measuring it wrong. Also I want to know how can I measure this 10000 times and take the average of those times. I hope to receive any feedback for my question.