Java Reference
In-Depth Information
9.20
Suppose that
s1
and
s2
are given as follows:
StringBuilder s1 =
new
StringBuilder(
"Java"
);
StringBuilder s2 =
new
StringBuilder(
"HTML"
);
Show the value of
s1
after each of the following statements. Assume that the state-
ments are independent.
a.
s1.append(
" is fun"
);
b.
s1.append(s2);
c.
s1.insert(
2
,
"is fun"
);
d.
s1.insert(
1
, s2);
e.
s1.charAt(
2
);
f.
s1.length();
g.
s1.deleteCharAt(
3
);
h.
s1.delete(
1
,
3
);
i.
s1.reverse();
j.
s1.replace(
1
,
3
,
"Computer"
);
k.
s1.substring(
1
,
3
);
l.
s1.substring(
2
);
9.21
Show the output of the following program:
public class
Test {
public static void
main(String[] args) {
String s =
"Java"
;
StringBuilder builder =
new
StringBuilder(s);
change(s, builder);
System.out.println(s);
System.out.println(builder);
}
private static void
change(String s, StringBuilder builder) {
s = s +
" and HTML"
;
builder.append(
" and HTML"
);
}
}
The
main
method can receive string arguments from the command line.
Key
Point
Perhaps you have already noticed the unusual header for the
main
method, which has the
parameter
args
of
String[]
type. It is clear that
args
is an array of strings. The
main
method is just like a regular method with a parameter. You can call a regular method by pass-
ing actual parameters. Can you pass arguments to
main
? Yes, of course you can. In the fol-
lowing examples, the
main
method in class
TestMain
is invoked by a method in
A
.
public class
A {
public static void
main(String[] args) {
String[] strings = {
"New York"
,
"Boston"
,
"Atlanta"
};
public class
TestMain {
public static void
main(String[] args)
{
for
(
int
i =
0
; i < args.length; i++)
System.out.println(args[i]);
TestMain.main(strings);
}
}
}
}
A
main
method is just a regular method. Furthermore, you can pass arguments from the
command line.
