How to sort a list of objects according to two parameters to compare at Java?

I have a class like that:

public class Zern extends Something{
 private int costA;
 private int costB;

 public int getcostA() {
     return costA;
 }

 public void setcostA(int costA) {
     this.costA = costA;
 }

 public int getcostB() {
     return costB;
 }

 public void setcostB(int costB) {
     this.costB = costB;
 }
}

I have a list that holds that kind of objects:

private List<Zern> zerns = new ArrayList<Zern>(MAX_ZERN_SIZE);

I will add new objects to my list however I always want to have a ordered list according to cost a and if there is an object at list which has the same cost with my object that I want to add I want to add that object according to their costB.

I mean:

Index of objects at list   0    1    2    3    4   5
CostA                     10   15   22   22   25  36
CostB                     26   12   17   19   23  44

If I want to add an object that has a costA 22 and costB 18, 
it will locate at index 3.

How can I do it effectively (because I will add an object to a sorted list so it means that I can use binary search - if it i开发者_C百科s possible I want to find a solution according to that) with Comparator or something like that?

Use Collections.sort with the following comparator:

Collections.sort(zerns, new Comparator<Zern>() {

    @Override
    public int compare(Zern z1, Zern z2) {
        if (z1.getcostA() == z2.getcostA()) {
            return z1.getcostB() == z2.getcostB() ? 0 : 
                z1.getcostB() < z2.getcostB() ? -1 : 1;
        } else {
            return z1.getcostA() < z2.getcostA() ? -1 : 1;
        }
    }
});

Update: If you do not need indexed access to your items you may want to use a sorted set implementation from the first place with a custom comparator:

TreeSet<Zern> zerns = new TreeSet<Zern>(new Comparator<Zern>() {

    @Override
    public int compare(Zern z1, Zern z2) {
        if (z1.getcostA() == z2.getcostA()) {
            return z1.getcostB() == z2.getcostB() ? 0 : 
                z1.getcostB() < z2.getcostB() ? -1 : 1;
        } else {
            return z1.getcostA() < z2.getcostA() ? -1 : 1;
        }
    }
});

Now objects can be added and your set will always remain sorted (note: I added a constructor and toString to your Zern class):

zerns.add(new Zern(10, 26));
System.out.println(zerns);     // => [(10,26)]
zerns.add(new Zern(22, 19));
System.out.println(zerns);     // => [(10,26), (22,19)]
zerns.add(new Zern(22, 17));
System.out.println(zerns);     // => [(10,26), (22,17), (22,19)]
zerns.add(new Zern(15, 12));
System.out.println(zerns);     // => [(10,26), (15,12), (22,17), (22,19)]

You can remove an item

zerns.remove(new Zern(22, 17));
System.out.println(zerns);     // => [(10,26), (15,12), (22,19)]

or remove the worst cost item

zerns.remove(zerns.last());
System.out.println(zerns);     // => [(10,26), (15,12)]

or get the best cost item via

System.out.println(zerns.first());    // => (10,26)

Just compare the first criteria. If they match, compare the second criteria:

public int compareTo(Zern other) {
   final int result;

    if (this.costA == other.costA) {
        if (this.costB > other.costB) {
            result = 1;
        } else if (this.costB < other.costB) {
            result = -1;
        } else {
            result = 0;
        }
    } else {
        if (this.costA > other.costA) {
            result = 1;
        } else if (this.costA < other.costA) {
            result = -1;
        } else {
            result = 0;
        }
    }

    return result;
}