Java中这种语法的等效含义是什么？

Question

Just a quick question about how to convert a certain line of code between c++ and Java. I've been learning about Neural Networks and I've been starting to write my own in the language I have the most experience with, Java. It's been pretty straightforward to translate the code from C++ to Java so far, however there's one little issue I've ran into. I'm puzzled by how to translate this specific line of code into a Java equivalent, and I can't find anything specific to this issue through searching.

The original code is:

Struct SNeuron {
   //the number of inputs into the neuron

   int m_NumInputs;
   //the weights for each input
   vector<double> m_vecWeight;
   //ctor
   SNeuron(int NumInputs);
};

and my code is:

public class SNeuron {

public int m_NumInputs; // the number of inputs into the neuron
public ArrayList<Double> m_vecWeight = new ArrayList<Double>(); // the weights for each input
// ctor

My question is, how do I convert:

SNeuron(int NumInputs);

into its Java equivalent? From what i've read, Structs don't seem to be a feature Java uses, so i'm just struggling a bit to understand what exactly that line of code actually does in the context it's used.

Answer 1

public class SNeuron 
{

// the number of inputs into the neuron

public int m_NumInputs;

// the weights for each input

public List<Double> m_vecWeight = new ArrayList<Double>();

// ctor
SNeuron(int NumInputs) {
   m_NumInputs = NumInputs;
}

Answer 2

Given the comments in code, I'm pretty sure the equivalent is:

public class SNeuron {
    public final double[] weights;

    public SNeuron(int numInputs) {
        weights = new double[numInputs];
    }
}

You don't really want to use a List<Double> , it will be much slower and take much more memory - each double in such a list becomes a full-fledged object with all associated overheads.

Answer 3

In C++, SNeuron(int NumInputs); is the declaration of a constructor taking an int , and this is contained within the class declaration.

You don't do that in Java - effectively all constructors, and all functions for that matter, are inlined in the class declaration. In other words

SNeuron(int NumInputs); // within the class declaration
SNeuron::SNeuron(int NumInputs) : m_NumInputs(NumInputs){} // In a translation unit

maps to

SNeuron(int NumInputs) {
   m_NumInputs = NumInputs;
}

but note that using m_ for Java fields is idiosyncratic.