Get a Character Values from a Map and add all to a String-CodePudding

I was wondering how i can get these values and put it together in a new String

class Rna {


    static Map<Character, Character> map = (Map<Character, Character>) Map.of(
            'G', 'C',
            'C', 'G',
            'T', 'A',
            'A', 'U'
    );

    String transcribe(String dnaStrand) {
        return dnaStrand.chars()
                .map(c -> map.get(c))
                .collect(StringBuilder::new, StringBuilder::appendCodePoint ,StringBuilder::append)
                .toString();
    }
}

transcribe should return an String like "AUGC". Now i`m getting this exception.

CodePudding user response：

I think the problem is that you use the String.chars() method which returns a stream of ints but you cannot expect autoboxing of an int to a Character.

The map doesn't contain int or Integer keys, so always will return null for the get.

As a solution you could try to cast c to a char or even create a Character instance manually:

.map(c -> map.get((char)c)) or .map(c -> map.get(Character.valueof((char)c))

CodePudding user response：

If you want to obtain map value, you can not have a String like "AUGC", may be "UAGC"? And you can read more about Collection, Map and LinkedHashMap. If you will try this code, all will be work.

public class Main {
    public static void main(String[] args) {


        Map<Character, Character> map = new LinkedHashMap();
            map.put('G', 'C');
        map.put( 'C', 'G');
                map.put( 'T', 'A');
                        map.put( 'A', 'U');


Test test = new Test();
        System.out.println(test.transcribe(map));
    }
}
public class Test {

    String transcribe(Map<Character, Character> map) {
        StringBuilder stringBuilder = new StringBuilder();
        for (Character ch : map.values()) {
            stringBuilder.append(ch);
        }
        return String.valueOf(stringBuilder.reverse());
    }
}

CodePudding user response：

Here is one way to do it. The method is called with a string of keys from your base/pair map. Any characters in that string map to null are filtered out. This presumes a map instance visible to the method. Otherwise it will need to be provided as an argument.

chars() provides a stream of characters
get the mapping for current character and convert to String
filter out any null values.
join String characters into long strand and return.

static String transcribe(String dnaStrand) {
    return dnaStrand.chars()
            .mapToObj(c -> String.valueOf(map.get((char)c)))
            .filter(str->!str.equals("null"))
            .collect(Collectors.joining());
}

System.out.println(transcribe("GCTA"));

will return and print

CGAU