传递字符串时，Java构造函数varargs发生冲突

Question

I have an issue with one of my class. I'm using a "varargs" constructor for unknown number of parameter.

public Groupe(String...nom){        
    for(String item:nom){   
        this.nom.add(item.toLowerCase());
    }
}

public Groupe(String nom){      
    String[] list =nom.split(",");
    for(String s : list){           
        this.nom.add(s.toLowerCase());
    }
}

The first constructor is called...that's fine, but there is a conflict when passing only ONE parameter with the second contructor. I would like to use the second constructor when passing only one string, and the first if 2 and more parameters.

I'd want to handle this new Groupe("Foo,Bar");

This is where I call it. I suspect the "error" comes from there

public void reserver(String...nom){
    Groupe gr = new Groupe(nom);
    passager.add(gr);       
}

I don't pass a String, but a Varargs (tab?)...

Answer 1

It should be fine, with the caveat that null can be converted to either String[] or String :

public class Test {

    public Test(String single) {
        System.out.println("Single");
    }

    public Test(String... multiple) {
        System.out.println("Multiple");
    }

    public static void main(String[] args) {
        new Test("Foo"); // Single
        new Test("Foo", "Bar"); // Multiple
        new Test(); // Effectively multiple
        // new Test(null); // Doesn't compile - ambiguous
        new Test((String) null); // Single
    }
}

EDIT: Now that you've shown us the calling code, that's definitely the problem:

public void reserver(String...nom){
    Groupe gr = new Groupe(nom);
    passager.add(gr);       
}

Here, the type of nom is String[] - so it will always call the first constructor. You've got an array of strings there - under what circumstances do you want to call the second constructor?

To be honest, given that the two constructors act significantly differently, I would actually make both constructors private, and provide static methods:

public static Groupe fromStringArray(String... nom)

public static Groupe fromCommaSeparatedString(String nom)

Then it will be absolutely clear what you're expecting in each case.

Answer 2

Maybe this can be a solution:

public Groupe(String...nom){       
    if (nom.length == 1) {
        add(nom[0].split(","));
    } else {
        add(nom);
    }
}

private void add(String[] list) {
    for(String s : list){           
        this.nom.add(s.toLowerCase());
    }
}

Answer 3

The varargs part can be empty. So you can get what you want with

public Groupe(String nom){
  String[] list = nom.split(",");
for(String s : list){           
    this.nom.add(s.toLowerCase());
}

 public Groupe(String nom1, String nom2, String...nom){   
this.nom.add(nom1);
this.nom.add(nom2);     
for(String item:nom)    
    this.nom.add(item.toLowerCase());
}

You could also, of course, use one ctor with an if statement on the length of the input array, splitting out cases 0 (not handled with the code above), 1, and > 1.

Answer 4

public class OverloadVarArgs {

public static void main(String... args){
    OverloadVarArgs a = new OverloadVarArgs("One Argument");
    OverloadVarArgs b = new OverloadVarArgs("Two", "Arguments");
    OverloadVarArgs c = new OverloadVarArgs("One, Argument");

}

public OverloadVarArgs(String a){
    System.out.println("Constructor 1");
}

public OverloadVarArgs(String... a){
    System.out.println("Constructor 2");
}
}

Output:

Constructor 1

Constructor 2

Constructor 1