Implement sorting by propertyX then by propertyY then by propertyZ in Java

Question

Given a the following class:

class Boo {
    private final String propertyX;
    private final Double propertyY;
    private final Integer propertyZ;
}

How would one go about constructing a Comparator which would result in instances of the class being ordered by propertyX then by propertyY then by propertyZ when Collection.sort(...) is called on a Collection<Boo>.

Is a Comparator the way to go?

possible duplicate of [Best way to compare objects by multiple fields?](http://stackoverflow.com/questions/369512/best-way-to-compare-objects-by-multiple-fields) — NPE, Jun 07 '12 at 15:35
I don't know why @sudocode deleted his answer. It pointed to [this excellent post](http://stackoverflow.com/questions/1421322/how-do-i-sort-a-list-with-multiple-sort-parameters/1421458#1421458) which answers your question. — missingfaktor, Jun 07 '12 at 15:53
Answer by @Yishai in this post demonstrates elegant use of enum for custom sorting and grouped sorting (multiple arguments) utilizing comparator chaining. — gunalmel, Sep 16 '12 at 04:25

score 4 · Accepted Answer · answered Jun 07 '12 at 15:39

4

You literally do what you suggest.

Comparator<Boo> booCmp = new Comparator<Boo>() {
    @Override
    public int compare(Boo o1, Boo o2) {
        int cmp = o1.propertyX.compareTo(o2.propertyX);
        if (cmp == 0)
            cmp = o1.propertyY.compareTo(o2.propertyY);
        if (cmp == 0)
            cmp = o1.propertyZ.compareTo(o2.propertyZ);
        return cmp;
    }
};

answered Jun 07 '12 at 15:39

Peter Lawrey

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Does this solution not break the rules for the Comparator.compare method? http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Comparator.html – auser Jun 07 '12 at 15:44
The only thing I can think of is if you don't implement `equals` similarly. Do you have something in mind? – Peter Lawrey Jun 07 '12 at 16:01

score 0 · Answer 2 · answered Jun 07 '12 at 15:40

0

@sudocode gave a good answer but I think it is even too much for you. Just implement your custom comparator that compares propertyX, then propertyY. Use this comparator with Collections.sort() or Arrays.sort()

answered Jun 07 '12 at 15:40

AlexR

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Implement sorting by propertyX then by propertyY then by propertyZ in Java

2 Answers2