Object-Oriented Techniques - Java - page 295

/** Default Constructor */
public

public EqualsDemo () {
this

this ( 0 , new new SomeClass ());

}

/** Demonstration "equals" method */
@Override
public public boolean boolean equals ( Object o ) {

iif ( o == this

this ) // optimization

return return true true ;

iif ( o == null null ) // No object ever equals null null

return return false false ;

// Of the correct class?
iif ( o . getClass () != EqualsDemo . class )
return return false false ;

EqualsDemo other = ( EqualsDemo ) o ; // OK, cast to this class

// compare field-by-field
iif ( int1 != other . int1 )

// compare primitives directly

false ;
iif (! obj1 . equals ( other . obj1 ))

return return false

// compare objects using their equals

return return false false ;

return return true true ;

}

}

Optimization: if same object, true by definition. Some say this is a premature optimiza-
tion.

If other object null, false by definition.

Co mpare class descriptors using ==; see following paragraph.

Op timization: compare primitives first. May or may not be worthwhile; may be better to
order by those most likely to differ—depends on the data and the usage.

Another common mistake to avoid: note the use of class descriptor equality (i.e.,
o.getClass() != EqualsDemo.class ) to ensure the correct class, rather than via in-
stanceof , as is sometimes erroneously done. The reflexive requirement of the equals()