Question

Consider the following Java interface.
public interface Converter<A, B> {
B convert(A xs);
}

(a) Write a default method convertAll in the interface Converter that takes
ArrayList<A> xs as input and returns a new ArrayList<B>. If the ArrayList
xs is [x1, : : :, xn], the method returns [convert(x1), : : :, convert(xn)].
In your method you may assume that xs is never null. If one of the calls to
convert throws an exception, your method should not catch it.

(b) Write a class StringConverter that implements the above interface suitably.
In particular, the class is supposed to have a method
public Integer convert(String word)
that behaves as follows:
If word is the null reference, an IllegalArgumentException is thrown.
Otherwise the method returns the length of word.

Answer 1

Converter.java

import java.util.ArrayList;

public interface Converter<A, B> {
   B convert(A xs);
  
   default ArrayList<B> convertAll(ArrayList<A> xs) {
       ArrayList<B> converted = new ArrayList<>();
       for(A item: xs) {
           converted.add(convert(item));
       }
       return converted;
   }
}

Code image:

import java.util.ArrayList; public interface Converter<A, B> { B convert(A xs); default ArrayList<B> convertAll(ArrayList<A> xs) { ArrayList<B> converted = new ArrayList<>(); for(A item: xs) { converted.add(convert(item)); return converted;

StringConverter.java

public class StringConverter implements Converter<String, Integer> {

   @Override
   public Integer convert(String xs) {
       if (xs == null)
           throw new IllegalArgumentException("INput can't be null");
       return xs.length();
   }
  
}

Code image:

public class StringConverter implements Converter<String, Integer> { @Override public Integer convert(String xs) { if (xs == null) throw new IllegalArgumentException ("INput can't be null"); return xs.length(); , ret,

StringConverterMain.java (added this to show how this is working)

import java.util.ArrayList;

public class StringConverterMain {

   public static void main(String[] args) {
       ArrayList<String> input = new ArrayList<>();
       input.add("First");
       input.add("Second");
       input.add("Third");
       input.add("Fourth");
       input.add("Fifth");
      
       StringConverter stringConverter = new StringConverter();
       ArrayList<Integer> converted = stringConverter.convertAll(input);
      
       for(int i = 0; i < converted.size(); i++) {
           System.out.println("Converted value of " + input.get(i) + " is " + converted.get(i));
       }

   }

}

Code image:

import java.util.ArrayList; public class String ConverterMain { public static void main(String[] args) { ArrayList<String> input = new ArrayList<>(); input.add("First"); input.add("Second"); input.add("Third"); input.add("Fourth"); input.add("Fifth"); StringConverter stringConverter = new StringConverter(); ArrayList<Integer> converted = stringConverter.convertAll(input); for(int i = 0; i < converted.size(); i++) { System.out.println("Converted value of " + input.get(i) + " is " + converted.get(i));

Sample execution:

Converted value of First is 5
Converted value of Second is 6
Converted value of Third is 5
Converted value of Fourth is 6
Converted value of Fifth is 5

Please give a thumbs up if this helped you in any way.