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Java Comparable, mutliple/different implenetations of compareTo() method

I have this class:

public class Sample implements Comparable<Sample> {
public String a;
public String b;
public String c;

public int compareTo (Sample sampleToCompare) {
int compResult = this.a.compareTo(sampleToCompare.a);
      return (compResult != 0 ? compResult : 
                   this.b.compareTo(sampleToCompare.b));    
    }
}

I want compareTo() to behave or sort using differen开发者_如何学JAVAt class properties depending if a flag is set.

So, if flag == 1 I'd like compareTo() to using property c, otherwise is flag == 0, whatever is currently in the method.

In other words, sort the same class in different ways.

I am not sure how to achieve this. Please help.

Also, please let me know if more information is needed from my side.


If you want to implement different kind of sorting, you should take a look at java.util.Comparator interface.

public class SampleComparatorA implement Comparator<Sample> {

    public int compare(Sample a, Sample b) {
        // Your sorting
    }
}

And use java.util.Collections.sort() method with the Comparator as the secound parameter instead.

Collections.sort(aSampleList, new SampleComparatorA());


How about:

public int compareTo(Sample sampleToCompare) {
    if (flag == 1) {
        return this.c.compareTo(sampleToCompare.c);
    }
    if (flag == 0) {
        // current stuff
    }
    ...
}

That's not a very object-oriented way to do it, though. Probably you should have two different comparators and a way to select them based on your "flag" value. Something like:

class Sample {
    private String a;
    private String b;
    private String c;
}

class ASampleComparator implements Comparator<Sample> {
    public int compare(Sample o1, Sample o2) {
        return o1.a.compareTo(o2.a);
    }
}

class BSampleComparator implements Comparator<Sample> {
    public int compare(Sample o1, Sample o2) {
        return o1.b.compareTo(o2.b);
    }
}

class CSampleComparator implements Comparator<Sample> {
    public int compare(Sample o1, Sample o2) {
        return o1.c.compareTo(o2.c);
    }
}

public Comparator<Sample> pickComparator(int flag) {
    switch (flag) {
        case 0:
            return new ASampleComparator();
        case 1:
            return new BSampleComparator();
        case 2:
            return new CSampleComparator();
        default:
            throw new IllegalArgumentException("Bad flag value: " + flag);
    }
}


You should make your flag static so the comparison will be consistent (as described in Effective Java, item 12), otherwise, you might get that a.compareTo(b) returns that a > b, but b.compareTo(a) returns that b > a. So the simplest implementation I can think about is:

public class Sample implements Comparable<Sample> {
public String a;
public String b;
public String c;
public static boolean my_flag = false;

public int compareTo (Sample sampleToCompare) {
    if (flag) {
        return this.c.compareTo(sampleToCompare.c);
    }
    int compResult = this.a.compareTo(sampleToCompare.a);
      return (compResult != 0 ? compResult : 
                   this.b.compareTo(sampleToCompare.b));    
    }
}
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