Return01.java
The call of a
void method
is performed by using the method name, by itself, as a program
statement. Observe in line 11 that
add1(n1,n2);
is the entire program statement. In line 12 a
call is made to method
add2
. A
return method
must be called in a program statement that uses
the returned value. In this case line 12 prints the value returned by method
add2
.
5
public class Return01
6
{
7
public static void main(String[ ] args)
8
{
9
int n1 = 100;
10
int n2 = 200;
11
add1(n1,n2);
12
System.out.println(add2(n1,n2));
13
}
14
15
public static void add1(int a, int b)
16
{
17
int result = a + b;
18
System.out.println(result);
19
}
20
21
public static int add2(int a, int b)
22
{
23
int result = a + b;
24
return result;
25
}
26
}
----jGRASP exec: java Return01
300
300
UNIT 2b
Using Objects Continued
Page 95
The previous program example showed that a return method was supposed to be used in a
program statement that used its value. Is that required? Will there be a syntax error if that is not
done? Much is learned about computer programming by making intentional mistakes. It is
beneficial to make various errors and observe the consequences. Program
Return02
is such an
example. In this program the return method
add
is called improperly.
Return02.java
Observe in line 11 that
add(n1,n2);
is the entire program statement. That is fine for a
void
method
, but not for a
return method
. Look at the first output box below. It shows that Java is
not excited. The program does compile. The second output shows an output of
Inside add
.
This proves that the method is called. However nothing is done with the
int
parameters.
5
public class Return02
6
{
7
public static void main(String[ ] args)
8
{
9
int n1 = 100;
10
int n2 = 200;
11
add(n1,n2);
12
}
13
14
public static int add(int a, int b)
15
{
16
System.out.println("Inside add");
17
int result = a + b;
18
return result;
19
}
20
}
----jGRASP exec: javac Return02.java
----jGRASP exec: java Return02
Inside add
Page 96
Java Programming for AP
®
Computer Science A
2020-2021 Edition
Return03.java
This program seems correct at first glance. There is a program statement in the
main
method
that displays the return value and everything necessary seems to be in the
add
method. The
problem is that method
add
declares in line 14 that a
boolean
value will be returned. Inside
the body of the method you see
result
returned and that is an
int
value. There will be no
output execution and Java objects with a syntax error message.
5
public class Return03
6
{
7
public static void main(String[ ] args)
8
{
9
int n1 = 100;
10
int n2 = 200;
11
System.out.println(add(n1,n2));
12
}
13
14
public static boolean add(int a, int b)
15
{
16
int result = a + b;
17
return result;
18
}
19
}
----jGRASP exec: javac Return03.java
Return03.java:17: error: incompatible types: int
cannot be converted to boolean
return result;
^
1 error
----jGRASP wedge2: exit code for process is 1.
The data type, in the heading of the return method,
must match the data type of the actual return value.
