Java Reference
In-Depth Information
Java calls this kind of variable a boolean , 5 and it can be assigned true or false ,
or you can give it math expressions using any of these operators, all of which
return either true or false :
Equal to (two equals signs)
Not equal to
Not (so “not true” is false, and “not false” is true)
Less than
Greater than
Less than or equal to
Greater than or equal to
And (true if both things are true)
Or (true if either thing is true)
For example, given these variables
int a = 10;
int b = 5;
String h = new String ( "Hello" );
boolean result = true;
boolean badone = false;
Java will figure out these comparisons:
a==10 is true
b==6 is false
a<20 is true
b>=5 is true
a>100 is false
result is true
!result is false (pronounced “not result”—“not” returns the opposite of a value)
result&&badone is false (pronounced “and”—true only if both are true)
result||badone is true (pronounced “or”—true if either is true)
But this next one won't do what you think it should; it will not be true :
h == "Hello" ; // Gotcha!
That one is tricky. For strings and objects (more on that in the next chapter),
use the equals function instead of the double equals sign ( == ), like this:
h.equals( "Hello" );
// is true
Named for George Boole, the British mathematician, who came up with these ideas in
the 1800's.
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