94 lines
2.7 KiB
Java
94 lines
2.7 KiB
Java
// collectiontopics/TypesForSets.java
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// (c)2017 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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protected int i;
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SetType(int n) { i = n; }
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@Override
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public boolean equals(Object o) {
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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 String toString() {
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return Integer.toString(i);
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}
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}
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class HashType extends SetType {
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HashType(int n) { super(n); }
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@Override
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public int hashCode() {
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return Objects.hashCode(i);
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}
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}
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class TreeType extends SetType
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implements Comparable<TreeType> {
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TreeType(int n) { super(n); }
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@Override
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public int compareTo(TreeType arg) {
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return Integer.compare(arg.i, i);
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// Equivalent to:
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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> void
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fill(Set<T> set, Function<Integer, T> type) {
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for(int i = 10; i >= 5; i--) // Descending
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set.add(type.apply(i));
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for(int i = 0; i < 5; i++) // Ascending
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set.add(type.apply(i));
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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(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(e.getMessage());
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}
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}
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}
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/* Output:
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[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
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[10, 9, 8, 7, 6, 5, 0, 1, 2, 3, 4]
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[10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
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[1, 6, 8, 6, 2, 7, 8, 9, 4, 10, 7, 5, 1, 3, 4, 9, 9,
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10, 5, 3, 2, 0, 4, 1, 2, 0, 8, 3, 0, 10, 6, 5, 7]
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[3, 1, 4, 8, 7, 6, 9, 5, 3, 0, 10, 5, 5, 10, 7, 8, 8,
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9, 1, 4, 10, 2, 6, 9, 1, 6, 0, 3, 2, 0, 7, 2, 4]
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[10, 9, 8, 7, 6, 5, 0, 1, 2, 3, 4, 10, 9, 8, 7, 6, 5,
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0, 1, 2, 3, 4, 10, 9, 8, 7, 6, 5, 0, 1, 2, 3, 4]
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[10, 9, 8, 7, 6, 5, 0, 1, 2, 3, 4, 10, 9, 8, 7, 6, 5,
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0, 1, 2, 3, 4, 10, 9, 8, 7, 6, 5, 0, 1, 2, 3, 4]
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SetType cannot be cast to java.lang.Comparable
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HashType cannot be cast to java.lang.Comparable
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*/
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