Conditional Structures and Loops - A Concise and Practical Introduction to Programming Algorithms in Java - page 38

- Similarly, for the || connector, in Expr1 || Expr2 do not evaluate Expr2 if
Expr1 is evaluated to true since we already know that in that case Expr1
|| Expr2 = true whatever the true/false value of expression Expr2 .

The lazy evaluation of boolean predicates will become helpful when manipu-
lating arrays later on. For now, let us illustrate these notions with a simple
example:

Program 2.2 Lazy evaluation of boolean predicates
class LazyEvaluation {

public static void main ( String [ ] args )

{ double x=3.14, y=0.0;
boolean test1 , test2 ;

// Here division by zero yields a problem
// But this is prevented in the && by first checking
whether the denominator is
// zero or not
if ((y!=0.0) && (x/y > 2.0))
{ // Do nothing
; }
else
{ // Block
test1=(y!=0.0) ;
test2=(x/y > 2.0) ;

System . out . println ( "Test1:" +test1+ " Test2:" +test2 ) ;
System . out . println ( "We did not evaluate x/y that is
equal to " +(x/y ) ) ;

}

// Here, again we do not compute x/y since the first term
is true
if (( y==0.0)

|| (x/y > 2.0))

{ // Block
System . out . println ( "Actually, again, we did not
evaluate x/y that is equal to " +(x/y ) ) ;

}

}

}

Running this program, we get the following console output:

Test1:false Test2:true
We did not evaluate x/y that is equal to Infinity
Actually, again, we did not evaluate x/y that is equal to Infinity