Can't return a Object[] casted as String[]

Question

public String[] getAllKeys (){

    Object[] keysCopy = new Object[keys.size()];
    keysCopy = keys.toArray();

    return ((String[])keysCopy());
}

Why this gives me Ljava.lang.Object; cannot be cast to [Ljava.lang.String??

Answer 1

It is because you have object array and Object[] cannot be cast to String[]. The reverse is possible. Its because Object IS NOT A String and String IS A Object.

If you are sure that the content of keys is collection of String, then you can use keys.toArray(new String[keys.size()]);

public String[] getAllKeys(){
    return keys.toArray(new String[keys.size()]);
}

Answer 2

`return Arrays.copyOf(keysCopy, keysCopy.length, String[].class);`

Answer 3

An Object[] is not a String[].

Answer 4

Try this, it works.

public String[] getAllKeys (){
Object[] keysCopy = new Object[keys.size()];
keysCopy = keys.toArray(new String[0]);
return (String[]) keysCopy;
}

For more you can read this [post] (How to convert object array to string array in Java)