63 lines
2.2 KiB
Java
63 lines
2.2 KiB
Java
import java.util.Arrays;
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import java.util.Collections;
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import java.util.Set;
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import java.util.TreeSet;
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public class Sets {
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public static void main(String[] args){
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Set<Integer> a = new TreeSet<>();
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//TreeSet sorts on natural ordering (or an optional comparator)
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//other options: HashSet (hashcode)
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// LinkedHashSet (insertion order)
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// EnumSet (optimized for enum values)
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//others at: http://download.oracle.com/javase/7/docs/api/java/util/Set.html
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Set<Integer> b = new TreeSet<>();
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Set<Integer> c = new TreeSet<>();
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Set<Integer> d = new TreeSet<>();
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a.addAll(Arrays.asList(1, 2, 3, 4, 5));
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b.addAll(Arrays.asList(2, 3, 4, 5, 6, 8));
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c.addAll(Arrays.asList(2, 3, 4));
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d.addAll(Arrays.asList(2, 3, 4));
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System.out.println("a: " + a);
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System.out.println("b: " + b);
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System.out.println("c: " + c);
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System.out.println("d: " + d);
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System.out.println("2 in a: " + a.contains(2));
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System.out.println("6 in a: " + a.contains(6));
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Set<Integer> ab = new TreeSet<>();
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ab.addAll(a);
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ab.addAll(b);
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System.out.println("a union b: " + ab);
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Set<Integer> a_b = new TreeSet<>();
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a_b.addAll(a);
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a_b.removeAll(b);
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System.out.println("a - b: " + a_b);
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System.out.println("c subset of a: " + a.containsAll(c));
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//use a.conatins() for single elements
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System.out.println("c = d: " + c.equals(d));
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System.out.println("d = c: " + d.equals(c));
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Set<Integer> aib = new TreeSet<>();
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aib.addAll(a);
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aib.retainAll(b);
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System.out.println("a intersect b: " + aib);
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System.out.println("add 7 to a: " + a.add(7));
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System.out.println("add 2 to a again: " + a.add(2));
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//other noteworthy things related to sets:
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Set<Integer> empty = Collections.EMPTY_SET; //immutable empty set
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//empty.add(2); would fail
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empty.isEmpty(); //test if a set is empty
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empty.size();
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Collections.disjoint(a, b); //returns true if the sets have no common elems (based on their .equals() methods)
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Collections.unmodifiableSet(a); //returns an immutable copy of a
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}
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}
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