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Sort a set of java objects by one value and remain unique by another value

I need to sort a set of java objects using the Level value of an integer. I also need to determine if this collection already contains an object called "title".

I believe the best choice for a collection is TreeSet, to have an ordered set of unique values.

I have an object with the attributes "level" and "title". It implements comparable values:

It overrides the Equals method (to verify that the object is already contained in the TreeSet by "title".

The code looks like this:

@Override
public boolean equals(Object arg0) {

    Artifact obj = (Artifact) arg0;

    if (this.getTitle().equals(obj.getTitle())) { 
        return true;
    }

    return false;
}

@Override
public int compareTo(Artifact aThat) {  

    final int BEFORE = -1;
    final int EQUAL = 0;
    final int AFTER = 1;

    if (this == aThat) return EQUAL;

    if (this.level < aThat.level) return BEFORE;
    if (this.level > aThat.level) return AFTER;

    assert this.equals(aThat) : "compareTo inconsistent with equals.";
    return EQUAL;
}

When I try to add values ​​to the list from arraylist with possible duplicate values. Contains does not seem to work, and objects are added to the TreeSet independently. Here is the code:

TreeSet<Artifact> subsetOfArtifacts = new TreeSet<Artifact>();

ArrayList<Artifact> allArtifacts = getArtifacts(); 
Iterator<Artifact> allArtifactsIter = allArtifacts.iterator();

while (allArtifactsIter.hasNext()) {
    Artifact artifact = (Artifact) allArtifactsIter.next();
    if (!subsetOfArtifacts.contains(artifact)) {
        subsetOfArtifacts.add(artifact);
    }
 }

, . ?

+3
4

equals(), hashCode() ! , Sets, undefined. :

@Override
public int hashCode() {
    return title.hashCode();
}

HashSet Set sortedSet = new TreeSet(set); . , .

, HashTables , equal(), hashCode() . javadoc hashCode()

hashCode:

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  • equals (Object), hashCode .
  • , , equals (java.lang.Object), hashCode . , Hashtables.
+3

, , equals .

public int compareTo(Artifact aThat) {

    final int BEFORE = -1;
    final int EQUAL = 0;
    final int AFTER = 1;

    if ( this == aThat ) return EQUAL;

    if (this.level < aThat.level) return BEFORE;
    if (this.level > aThat.level) return AFTER;
    return this.getTitle().compareTo(aThat.getTitle());

//        assert this.equals(aThat) : "compareTo inconsistent with equals.";

//    return EQUAL;
}

, Bohemian, hashCode(), equals(), , TreeSet .

+1

RTFM: D javadoc TreeSet : " , , ( ), , "

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2 -.

0

compareTo , , , , , , . - :

@Override
public int compareTo(Artifact aThat) 
{
    final int BEFORE = -1;
    final int EQUAL = 0;
    final int AFTER = 1;

    if ( this == aThat ) return EQUAL;

    if( this.level < aThat.level ) return BEFORE;
    if( this.level > aThat.level ) return AFTER;

    int compare = this.getTitle().compareTo(aThat.getTitle());

    if( compare != EQUAL ) return compare;

    assert this.equals(aThat) : "compareTo inconsistent with equals.";

    return EQUAL;
}

rob .

0

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