变换集 <Keyword> 放入String []

Question

I have an object Keyword that stores a String with the text of the keyword and a set o keywords ( Set<Keyword> ) that I need to transform into a String array. Is there a quick/easy way to do this or I need to iterate the set and add each keyword one by one?

EDIT:

For those asking for Keyword class:

@Entity
public class Keyword {

    // ...

    @Basic
    private String value;

    // ...

    // Getters & Setters

}

Answer 1

Try this:

 
 
 
  
  String[] arr = set.toArray(new String[set.size()]);
 
  

... is what I would have said, if you had a Set<Object> .

---

No, there is no way to directly convert a Set<Keyword> to a String[] since there is no direct relationship between Keyword and String . You will have to iterate over the set:

String[] arr = new String[set.size()];
int i = 0;
for (Keyword word : set)
    arr[i++] = word.toString();

Answer 2

Every class that implements Collection intefrace (and that includes Set ) has toArray() method:

String[] array= set.toArray(new String[0]);

---

In case of a set that is parametrized with some other type, eg Set<Keyword> you would have to do something like:

Keyword[] array= set.toArray(new Keyword[0]);
String[] stringArray= new String[array.length];

for (int i=0; i<array.length; i++) {
    stringArray[i]= array[i].getThatString();
}

Answer 3

If you use Guava , you may use this:

Lists.transform(Lists.newArrayList(theSet), Functions.usingToString())
    .toArray(new String[theSet.size()])

And this only scratches the surface of what Guava can actually do.

Answer 4

There is no specific way to do this . You can either convert Set to Object[] using set.toArray and then iterate over the array or iterate over the set directly

Answer 5

You may need to add toString() method to your Keyword class as shown below. Or you can use a separate transformer class/method.

class Keyword {
    private String value;

    Keyword(String v) {
        this.value = v;
    }

    public String toString() {
        return value;
    }
}

.

I would say iterate the set and add each keyword one by one is your best possible strategy.

System.out.println(toStringArray(set));

.

private static String[] toStringArray(Collection<?> set) {
    String[] arr = null;
    if (set != null) {
        arr = new String[set.size()];
        int i = 0;
        for (Object o : set) {
            arr[i++] = o.toString();
        }
    }
    return arr;
}

.

However if you really want, you can have a dirty workaround as shown below. Only issue here is that your keyword value cannot contain comma ( , ) as it is used by split() method.

String str = set.toString();
str = str.substring(1, str.length() - 1);
String[] asStringArray = str.split(",");
System.out.println(asStringArray);