53 lines
1.7 KiB
Java
53 lines
1.7 KiB
Java
// containersindepth/ReadOnly.java
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// ©2016 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://mindviewinc.com/Books/OnJava/ for more book information.
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// Using the Collections.unmodifiable methods.
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import java.util.*;
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import onjava.*;
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public class ReadOnly {
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static Collection<String> data =
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new ArrayList<>(Countries.names(6));
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public static void main(String[] args) {
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Collection<String> c =
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Collections.unmodifiableCollection(
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new ArrayList<>(data));
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System.out.println(c); // Reading is OK
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//! c.add("one"); // Can't change it
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List<String> a = Collections.unmodifiableList(
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new ArrayList<>(data));
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ListIterator<String> lit = a.listIterator();
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System.out.println(lit.next()); // Reading is OK
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//! lit.add("one"); // Can't change it
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Set<String> s = Collections.unmodifiableSet(
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new HashSet<>(data));
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System.out.println(s); // Reading is OK
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//! s.add("one"); // Can't change it
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// For a SortedSet:
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Set<String> ss = Collections.unmodifiableSortedSet(
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new TreeSet<>(data));
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Map<String,String> m = Collections.unmodifiableMap(
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new HashMap<>(Countries.capitals(6)));
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System.out.println(m); // Reading is OK
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//! m.put("Ralph", "Howdy!");
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// For a SortedMap:
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Map<String,String> sm =
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Collections.unmodifiableSortedMap(
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new TreeMap<>(Countries.capitals(6)));
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}
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}
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/* Output:
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[ALGERIA, ANGOLA, BENIN, BOTSWANA, BURKINA FASO, BURUNDI]
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ALGERIA
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[BENIN, BOTSWANA, ANGOLA, BURKINA FASO, ALGERIA, BURUNDI]
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{BENIN=Porto-Novo, BOTSWANA=Gaberone, ANGOLA=Luanda,
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BURKINA FASO=Ouagadougou, ALGERIA=Algiers,
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BURUNDI=Bujumbura}
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*/
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