Converting CharSequence[] and CharSequence[]

Question

I always thought CharSequence[] and String[] were essential the same, however :

I have some code that has the following :

CharSequence[] mEntries;
...
String[] mEntriesString = (String[]) mEntries;
ListAdapter adapter = new ArrayAdapter<String>(getContext(), R.layout.two_lines_list_preference_row, mEntriesString)

When the code runs I get

java.lang.ClassCastException: java.lang.CharSequence[] cannot be cast to java.lang.String[]

So two questions ?

why can this cast not happen
why does the ArrayAdapter not allow for a CharSequence[] in it's constructor.

nothing prevent an arrayadapter to use a CharSequence[] as a parameter. — njzk2
– njzk2, Commented Feb 20, 2013 at 15:33
When I try I get the following : The constructor ArrayAdapter<String>(Context, int, CharSequence[]) is undefined — BENBUN Coder
– BENBUN Coder, Commented Feb 20, 2013 at 15:36
as @jlordo pointed out, you type your arrayadapter with String. — njzk2
– njzk2, Commented Feb 20, 2013 at 16:29

Subhrajyoti Majumder · Accepted Answer · 2013-02-20 15:35:08Z

6

CharSequence is interface which String, StringBuffer, StringBuilder classes implements. So CharSequence can hold any of this implementation class's Object And CharSequence#toString returns String, try -

String[] mEntriesString = new String[mEntries.length];
int i=0;
for(CharSequence ch: mEntries){
    mEntriesString[i++] = ch.toString(); 
}

edited Feb 20, 2013 at 15:35

answered Feb 20, 2013 at 15:29

Subhrajyoti Majumder

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1 Comment

njzk2 Over a year ago

(not by me so i can only guess, but I'd say it's because it's useless and overkill?)

Tomislav Novoselec · Accepted Answer · 2013-02-20 15:29:39Z

1

CharSequence is an Interface. String class implements that interface. So, you cannot cast it to String, the same way you cannot cast List to ArrayList, because it doesn't have to be an instance of that concrete class

answered Feb 20, 2013 at 15:29

Tomislav Novoselec

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2 Comments

jlordo Over a year ago

You can cast List to ArrayList, the ClassCastException will only happen if the referenced object is not of type ArrayList. See: List list = new ArrayList(); ArrayList a = (ArrayList) list; LinkedList b = (LinkedList) list; The first cast will work, the second one will fail.

Tomislav Novoselec Over a year ago

@jlordo yes, I agree. I should've wrote that you cannot cast it SAFELY, unless you use instanceof operator

Michał Ziober · Accepted Answer · 2013-02-20 15:50:15Z

You can not cast reference CharSequence[] into String[].

You can cast it only in that situation:

        CharSequence[] charSequencesAsString = new String[] { "test" };
        String[] result = (String[]) charSequencesAsString;
        System.out.println(Arrays.toString(result));

Safe way to solve your problem:

public static void main(String[] args) {

    CharSequence[] charSequencesAsString = new String[] { "test" };
    CharSequence[] charSequencesAsCharSequence = new CharSequence[] { "test" };
    CharSequence[] charSequencesAsStringBuilder = new StringBuilder[] { new StringBuilder("Test") };

    String[] stringsFromStrings = convertToStringArray(charSequencesAsString);
    String[] stringsFromCharSequence = convertToStringArray(charSequencesAsCharSequence);
    String[] stringsFromStringBuilder = convertToStringArray(charSequencesAsStringBuilder);

    System.out.println("Same array after conversion: " + (stringsFromStrings == charSequencesAsString));
    System.out.println("Same array after conversion: " + (stringsFromCharSequence == charSequencesAsCharSequence));
    System.out.println("Same array after conversion: " + (stringsFromStringBuilder == charSequencesAsStringBuilder));
}

public static String[] convertToStringArray(CharSequence[] charSequences) {
    if (charSequences instanceof String[]) {
        return (String[]) charSequences;
    }

    String[] strings = new String[charSequences.length];
    for (int index = 0; index < charSequences.length; index++) {
        strings[index] = charSequences[index].toString();
    }

    return strings;
}

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