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Specialized for type MyClass

This Comparator is specialized to compare two objects of the class named MyClass . The first two statements in Listing 6 above confirm that both of the incoming objects are of type MyClass . If either object is not of that type, an exception is thrown.

General behavior of compare method

The general description of the behavior of the compare method as provided by Oracle is shown below:

"Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, orgreater than the second."

Implementation of required behavior

This behavior is accomplished by the code shown in Listing 7 . In this case, the comparison is based solely on the values of the instance variablenamed data in each of the two objects.

Depending on which object contains the larger value in its instance variable, a value of 1 or -1 is returned. If the two values are equal, a value of 0is returned.

(Note that it is up to the author of the compare method to decide what constitutes larger. This gives the author of themethod a great deal of control over the results of a sorting operation.)
Listing 7 . Implementation of required behavior.
if(((MyClass)o1).data<((MyClass)o2).data) return -1;if(((MyClass)o1).data>((MyClass)o2).data) return 1;else return 0; }//end compare()

Other stipulations

The documentation for the compare method contains several other stipulations regarding the behavior of the method. While I believe thatthis version of the compare method meets all of those stipulations, I haven't taken the time to test it fully. Therefore, it is possible that itmay not meet all of the stipulations in terms of its behavior.

The equals method

Every new class inherits a default version of the equals method from the class named Object. Therefore, a new class that implements the Comparator interface already has such a method. The new class is free to override the inherited version, or to simply make use of the inheritedversion. Here is what Oracle has to say on the subject:

"Note that it is always safe not to override Object.equals(Object). However, overriding this method may, in some cases, improve performance byallowing programs to determine that two distinct Comparators impose the same order."

Overridden equals method

I decided, for purposes of illustration, to go ahead and override the equals method. However, my overridden version, as shown in Listing 8 isn't very significant. It simply confirms that an object being comparedfor equality to a Comparator object is instantiated from the same class.

Since the Comparator object doesn't contain any instance variables, there isn't much more to be tested for equality.

Listing 8 . The overridden equals method.
public boolean equals(Object o){ if(!(o instanceof TheComparator))return false; else return true;}//end overridden equals() }//end class TheComparator

The program output

Finally, the code shown in Listing 9 uses an Iterator to display the contents of the populated TreeSet object.

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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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