ReadOnly.java

package ch11collection;//: containers/ReadOnly.java
// Using the Collections.unmodifiable methods.

import java.util.*;

import net.mindview.util.*;

import static net.mindview.util.Print.*;

/**
 * 只读的集合类
 */
public class ReadOnly {
    static Collection<String> data = new ArrayList<String>(Countries.names(6));

    /**
     * 获取不可更改的集合类
     */
    public static void unmodify() {
        Collection<String> c = Collections
                .unmodifiableCollection(new ArrayList<String>(data));
        print(c); // Reading is OK
        // ! c.add("one"); // Can't change it

        List<String> a = Collections.unmodifiableList(new ArrayList<String>(
                data));
        ListIterator<String> lit = a.listIterator();
        print(lit.next()); // Reading is OK
        // ! lit.add("one"); // Can't change it

        Set<String> s = Collections.unmodifiableSet(new HashSet<String>(data));
        print(s); // Reading is OK
        // ! s.add("one"); // Can't change it

        // For a SortedSet:
        Set<String> ss = Collections.unmodifiableSortedSet(new TreeSet<String>(
                data));

        Map<String, String> m = Collections
                .unmodifiableMap(new HashMap<String, String>(Countries
                        .capitals(6)));
        print(m); // Reading is OK
        // ! m.put("Ralph", "Howdy!");

        // For a SortedMap:
        Map<String, String> sm = Collections
                .unmodifiableSortedMap(new TreeMap<String, String>(Countries
                        .capitals(6)));
    }
} /*
 * Output: [ALGERIA, ANGOLA, BENIN, BOTSWANA, BULGARIA, BURKINA FASO] ALGERIA
 * [BULGARIA, BURKINA FASO, BOTSWANA, BENIN, ANGOLA, ALGERIA] {BULGARIA=Sofia,
 * BURKINA FASO=Ouagadougou, BOTSWANA=Gaberone, BENIN=Porto-Novo, ANGOLA=Luanda,
 * ALGERIA=Algiers}
 */// :~