java - 设置交集

Question

我想将交集(使用此方法 http://google-collections.googlecode.com/svn/trunk/javadoc/com/google/common/collect/Sets.html )应用于包含非原始对象的集合。我写了这段代码，但我发现交集是空的..

        Concept a = new Concept("Dog");
        Concept b = new Concept("Tree");
        Concept c= new Concept("Dog");
        HashSet<Concept> set_1 = new HashSet<Concept>();
        HashSet<Concept> set_2 = new HashSet<Concept>();

        set_1.add(a);
        set_1.add(b);
        set_1.add(c);
        SetView<Concept> inter = Sets.intersection(set_1,set_2);
        System.out.println(inter.size());  ----> I HAVE ZERO !!!

Concept类只包含一个String类型的私有(private)成员以及get和set方法..我没有equals()和hashCode ().

Answer 1

这按预期工作(注意 Concept 上的 equals 和 hashCode)

package com.stackoverflow.so19634761;

import com.google.common.collect.Sets;
import com.google.common.collect.Sets.SetView;

import java.util.Set;

public class ISect {
    public static void main(final String[] args) {
        final Concept a = new Concept("Dog");
        final Concept b = new Concept("Tree");
        final Concept c= new Concept("Dog");
        final Set<Concept> set1 = Sets.newHashSet(a);
        final Set<Concept> set2 = Sets.newHashSet(b, c);

        final SetView<Concept> inter = Sets.intersection(set1, set2);
        System.out.println(inter); // => [Concept [data=Dog]]
    }

    private static class Concept {

        private final String data;

        // below this point code was generated by eclipse.

        public String getData() {
            return data;
        }

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + ((data == null) ? 0 : data.hashCode());
            return result;
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj)
                return true;
            if (obj == null)
                return false;
            if (getClass() != obj.getClass())
                return false;
            Concept other = (Concept) obj;
            if (data == null) {
                if (other.data != null)
                    return false;
            } else if (!data.equals(other.data))
                return false;
            return true;
        }

        public Concept(String data) {
            this.data = data;
        }   

        @Override
        public String toString() {
            return "Concept [data=" + data + "]";
        }
    }
}