Java Reference
In-Depth Information
assert false : "daysInMonth has the value " + daysInMonth;
Now you should see that the output includes the string resulting from the second expression in the
assertion statement:
java.lang.AssertionError: daysInMonth has the value 32
at TryAssertions.main(TryAssertions.java:1)
Exception in thread "main"
We will use assertions from time to time in the examples in subsequent chapters.
Summary
In this chapter you have learned about all of the essential mechanisms for making decisions in Java.
You have also learned all of the looping facilities that you have available when programming. The
essential points we have covered are:
You can use
relational operators
to compare values, and such comparisons result in values of
either
true
or
false
.
You can combine basic comparisons and logical variables in more complex logical
expressions by using
logical operators
.
The
if
statement is a basic decision making tool in Java. It enables you to choose to execute a
block of statements if a given logical expression has the value
true
. You can optionally execute
another block of statements if the logical expression is
false
by using the
else
keyword.
You can use the
conditional operator
to choose between two expressions depending on the
value of a logical expression.
You can use the
switch
statement to choose from a fixed number of alternatives.
The variables in a method come into existence at the point at which you declare them, and
cease to exist after the end of the block that immediately encloses their declaration. The
program extent where the variable is accessible is the
scope
of the variable.
You have three options for repeating a block of statements, a
for
loop, a
while
loop or a
do
while
loop.
The
continue
statement enables you to skip to the next iteration in the loop containing the
continue
statement.
The labeled
continue
statement enables you to skip to the next iteration in a loop enclosing
the labeled
continue
that is identified by the label. The labeled loop need not be that
immediately enclosing the labeled
continue
.
The
break
statement enables you to break out of a loop or block of statements in which it appears.
The labeled
break
statement enables you to break out of a loop or block of statements that
encloses it that is identified by the label. This is not necessarily the block that encloses it directly.
You use an assertion statement to verify logical conditions that should always be
true
, or as
code in parts of a program that should not be reached, but theoretically can be.
