84 lines
2.3 KiB
Java
84 lines
2.3 KiB
Java
// understandingcollections/TypesForSets.java
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// (c)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://OnJava8.com for more book information.
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// Methods necessary to put your own type in a Set
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import java.util.*;
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import java.util.function.*;
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import java.util.Objects;
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class SetType {
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int i;
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public SetType(int n) { i = n; }
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@Override
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public boolean equals(Object o) {
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if (o == this) return true;
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return o instanceof SetType &&
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Objects.equals(i, ((SetType)o).i);
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}
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@Override
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public int hashCode() { return Objects.hash(i); }
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@Override
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public String toString() { return Integer.toString(i); }
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}
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class HashType extends SetType {
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public HashType(int n) { super(n); }
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}
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class TreeType extends SetType
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implements Comparable<TreeType> {
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public TreeType(int n) { super(n); }
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@Override
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public int compareTo(TreeType arg) {
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return (arg.i < i ? -1 : (arg.i == i ? 0 : 1));
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}
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}
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public class TypesForSets {
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static <T> Set<T>
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fill(Set<T> set, Function<Integer, T> type) {
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for(int i = 0; i < 10; i++)
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set.add(type.apply(i));
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return set;
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}
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static <T> void
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test(Set<T> set, Function<Integer, T> type) {
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fill(set, type);
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fill(set, type); // Try to add duplicates
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fill(set, type);
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System.out.println(set);
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}
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public static void main(String[] args) {
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test(new HashSet<>(), HashType::new);
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test(new LinkedHashSet<>(), HashType::new);
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test(new TreeSet<>(), TreeType::new);
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// Things that don't work:
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test(new HashSet<>(), SetType::new);
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test(new HashSet<>(), TreeType::new);
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test(new LinkedHashSet<>(), SetType::new);
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test(new LinkedHashSet<>(), TreeType::new);
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try {
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test(new TreeSet<>(), SetType::new);
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} catch(Exception e) {
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System.out.println("Expected: " + e.getMessage());
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}
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try {
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test(new TreeSet<>(), HashType::new);
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} catch(Exception e) {
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System.out.println("Expected: " + e.getMessage());
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}
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}
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}
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/* Output:
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[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
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[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
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[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
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[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
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[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
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[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
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[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
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Expected: SetType cannot be cast to java.lang.Comparable
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Expected: HashType cannot be cast to java.lang.Comparable
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*/
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