Cannot create Set from String array

Question

I've been staring at the screen the last 5 minutes and can't seem to figure out what I'm doing wrong:

class Example {

    private final Set<String> values;

    public Example(String... values) {
        values = new HashSet<String>(Arrays.asList(values));
    }
}

I'm surprised why the String[] cannot be converted to List<String> to initialize the HashSet<String> with it.

I'm getting the build error:

incompatible types: java.util.HashSet<java.lang.String> cannot be converted to java.lang.String[]

What's wrong with my assignment?

Answer 1

You're missing a qualification to actually access the private field. Currently you're trying to reassign the parameter passed to the constructor. Instead you should use the following code:

public Example(String... values) {
     this.values = new HashSet<String>(Arrays.asList(values));
}

This can be shortened even further by using the "Diamond Operator", which is avaliable since Java 7:

public Example(String... values) {
     this.values = new HashSet<>(Arrays.asList(values));
}

Answer 2

This is how you can do it

 if(values != null)
      this.values = new HashSet<>(Arrays.asList(values));
 else
      this.values = Collections.emptySet();

Add the if(values != null) check before the assignment.Whenever you use var args you are exposing a contract which will permit your clients to create an valid Example object without any arguments.If you want to avoid that from happening then just use String[] values directly and throw an exception incase if it is null

Answer 3

Other answers have addressed the cause, but wouldn't it be better to simply rename the parameter to avoid the shadowing?