CODEWITHSUNDEEP
javaandroid
BENBUN Coder
BENBUN Coder

Reputation: 4881

Converting CharSequence[] and CharSequence[]

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 ?

Upvotes: 1

Views: 9097

Answers (3)

Michał Ziober
Michał Ziober

Reputation: 38625

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;
}

Upvotes: 1

Subhrajyoti Majumder
Subhrajyoti Majumder

Reputation: 41200

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(); 
}

Upvotes: 6

Tomislav Novoselec
Tomislav Novoselec

Reputation: 4620

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

Upvotes: 1

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