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1.00 Lecture 3
Operators, Control
Reading for next time: Big Java: sections 6.16.4
Skip all the advanced topics, hints, etc.
Main()
•
About main():
–
In each Java program there is a just a single main()
method, no matter how many classes there are.
•
The main() method is often in a class that has no other
methods, by convention. It can be in any class, though
some choices would seem unnatural.
–
main() tells Java where to start the program; it’s just a
naming convention
•
It could easily have been called “StartHere”
–
In early examples we have only one class, so it will
seem there’s a main() method in each class.
Nope.
–
Main() at a later point will be minimalist:
•
Main() does the least possible work to get the program
running and then hands off all the remaining work to
objects and their methods.
•
For now, since we haven’t covered classes and objects,
we’ll do everything in main() for a little while longer.
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View Full DocumentLogical Operators
•
Produce results of type boolean
•
Comparisons use 9 operators:
Equal
==
Not equal
!=
Less than
<
Less than or
equal
<=
Greater than
>
Greater than or
equal
>=
Logical and
&&
Logical or

Not
!
// Example
int c= 0, b= 3;
if (c != 0 && b/c > 5) System.out.println(“Buy this stock”);
// Short circuit evaluation: quit after answer determined
boolean buy= true;
if (!buy  c == 0) System.out.println(“Nah, don’t buy”);
Assignment Operators
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Assignment is not the same as equality
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= is not the same as ==
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Assignments are expressions:
int x, y;
x= y= 5;
// Same as x = (y= 5); assoc from R to L
•
Shortcut forms exist:
int x= 5, y= 3;
x += y;
// Same as x= x + y;
// This means take current value of x (5), add y (3), and
// set x to a new value of 8
•
Shortcut forms include +=, =, *=, /=, %= :
x /= y;
// Same as x= x / y;
x %= y;
// Same as x= x % y;
•
Other shortcut forms are ++ and  :
x++;
// Same as x= x + 1;
y= x;
// Same as x= x1; y = x; (More later)
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 Spring '05
 GeorgeKocur

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