Java - Collections Framework - How to Use Comparator? - Java

Both TreeSet and TreeMap store elements in sorted order. However, it is the comparator that defines precisely what sorted order means.

The Comparator interface defines two methods: compare( ) and equals( ). The compare( ) method, shown here, compares two elements for order −

The compare Method

obj1 and obj2 are the objects to be compared. This method returns zero if the objects are equal. It returns a positive value if obj1 is greater than obj2. Otherwise, a negative value is returned.

By overriding compare( ), you can alter the way that objects are ordered. For example, to sort in a reverse order, you can create a comparator that reverses the outcome of a comparison.

The equals Method

The equals( ) method, shown here, tests whether an object equals the invoking comparator −

obj is the object to be tested for equality. The method returns true if obj and the invoking object are both Comparator objects and use the same ordering. Otherwise, it returns false.

Overriding equals( ) is unnecessary, and most simple comparators will not do so.


This will produce the following result −


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