comparator | Tech Tips & Tricks

Do Comparators Work In Android?

June 20, 2011 by blogmeister·2 Comments

Since the Comparator class is part of the Java programming language, Android should do too. However, my experience with using them seem to indicate that it may not work all the time. Even I think it does not work in Android.

Has anyone else experienced this? Or even used it and worked? I made a Comparator class and ran it in Java’s runtime environment. It worked correctly. When I used the same class and sorted an ArrayList object in the Android emulator, it did not work. The sorting was different.

Now, I have no idea why. I always thought that there was something wrong with my custom Comparator class because the output in the Android emulator was always wrong. When I ran it in the JRE (since it was faster), the output was correct.

There should not be any rules to using comparators in the Android emulator. How they are used should be the same as when used in the Java Runtime Environment.

Please share your thoughts. Your inputs are highly appreciated and may help me know the limitations and what ifs when using a Comparator class in an Android emulator.

Java: Sort Date Using Comparator

September 25, 2009 by blogmeister·1 Comment

Comparing Dates using the Comparator class in Java is not the same as comparing Strings. Even if you convert the Date’s getTime() method to a Long object, using compareTo() on those two Long objects will not do the trick. However, you can make use of the long values right away.

Check out the code.

Comparator date_comparator = new Comparator() {
    @Override
    public int compare(Date s1, Date s2){
        long n1 = s1.getTime();
        long n2 = s2.getTime();
        if (n1 < n2) return -1;
        else if (n1 > n2) return 1;
        else return 0;
    }
};

Comparator date_comparator = new Comparator() {

@Override

public int compare(Date s1, Date s2){

long n1 = s1.getTime();

long n2 = s2.getTime();

if (n1 < n2) return -1;

else if (n1 > n2) return 1;

else return 0;

}

};

Sort A Vector Using Comparator In Java

May 24, 2009 by blogmeister·5 Comments

If your Vector object contains a set of custom class objects with a property of int and you want it to sort in ascending order, you can do it like this.

Collections.sort(vect, new Comparator() {
  public int compare(Object a, Object b) {
    return ( new Integer(((MyClass) a).getNumber()) ).compareTo( new Integer(((MyClass) b).getNumber()));
  }
});

Collections.sort(vect, new Comparator() {

public int compare(Object a, Object b) {

return ( new Integer(((MyClass) a).getNumber()) ).compareTo( new Integer(((MyClass) b).getNumber()));

}

});

The getNumber() method contains the int value that will be used as basis to sort them in ascending order. To sort them in descending order, simply add a - (negative) sign after the keyword return.

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Tag: comparator

Do Comparators Work In Android?

Java: Sort Date Using Comparator

Sort A Vector Using Comparator In Java