[effective_java] --- generic ---

 

 

• item 30의 재귀적 한정타입을 사용한 max메서드

package effectivejava.chapter5.item30;
import java.util.*;

// Using a recursive type bound to express mutual comparability (Pages 137-8)
public class RecursiveTypeBound {
    // Returns max value in a collection - uses recursive type bound
    public static <E extends Comparable<E>> E max(Collection<E> c) {
        if (c.isEmpty())
            throw new IllegalArgumentException("Empty collection");

        E result = null;
        for (E e : c)
            if (result == null || e.compareTo(result) > 0)
                result = Objects.requireNonNull(e);

        return result;
    }

    public static void main(String[] args) {
        List<String> argList = Arrays.asList(args);
        System.out.println(max(argList));
    }
}

 

 

 

• item 31에서 다루고 있는 한정적 와일드 카드

package effectivejava.chapter5.item30;
import java.util.*;

// Generic union method and program to exercise it  (Pages 135-6)
public class Union {

    // Generic method
    public static <E> Set<E> union(Set<E> s1, Set<E> s2) {
        Set<E> result = new HashSet<>(s1);
        result.addAll(s2);
        return result;
    }

    // Simple program to exercise generic method
    public static void main(String[] args) {
        Set<String> guys = Set.of("Tom", "Dick", "Harry");
        Set<String> stooges = Set.of("Larry", "Moe", "Curly");
        Set<String> aflCio = union(guys, stooges);
        System.out.println(aflCio);
    }
}

 

 

 

 

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