Functions in Java provide a way to modularize code. How do you eat an
elephant? One bite at a time. If you write your Java code
in
concise and neat functions and classes, you will maximize the amount of
code you can reuse and minimize your work load. You
will also be able to deal with complex programming tasks by using
recursive functions and breaking larger tasks into a series
of functions that, as a sum total, will solve a much larger problem. It
is common after pseudo-coding a project out to "stub out"
its functions. That is to say, after thinking about how you want to
modularize it and break it apart, you create the project by coding
all all of its functions as empty functions. Although there is no code
to do anything at this stage, it will help you organize your
project and give you a starting point. You then go back and code out
each function one by one, debugging as you go.
The biggest mistake people make in programming (C++, Java or any other
kind) is that they try to debug too much code at one time.
They will type in a hundred, or some even a thousand lines of code
before they debug. Then they are overwhelmed by the enormous list of
errors returned when they build and compile their project. This is
compounded by the fact that compilers (both C++, Java and otherwise)
don't always get it right. The compiler makes an educated guess, but
many times may tell you one thing is wrong when it's
really another. Missing or extraneous braces and semicolons are
notorious for this - causing the compiler to tell you your bugs are
one thing when really they are another. You have to learn to "desk
check", that is, to step through the code in your head. You also
have to learn to write and debug small parts of your program as you go.
This is where the usefulness of functions comes in.
Functions have return types and take arguments. They may also return
"void" and take no arguments. They begin and end with a curly brace. It
is a good practice then defining a function to add a closing brace every
time you add an opening brace. If you forget, you will have issues. Once
you define a function, you must "call" it or invoke it from elsewhere in
the program to get it to execute.
Example 1 - No return value
(void) and no arguments:
import
javax.swing.*;
public
class
DaFunkShen
{
public
void main(String[] args)
{
System.out.println("In main().");
DoStuff();
//invoking function
System.exit(0);
System.out.println("In
main().");
}//close main() function
//Defining
a function
public
void DoStuff()
{
System.out.println("Inside function. Doing stuff...");
}//close main() function
}//close
AFunction class |
Notice: Here we
define a function under main(), "DoStuff()" and invoke it from within
main().
Example 2 - Returns a value,
takes no arguments:
import
javax.swing.*;
public
class
DaFunkShen
{
public
void main(String[] args)
{
String WhatWasSaid = "";
System.out.println("In main().");
WhatWasSaid = DoStuff();
//invoking function
System.out.println(WhatWasSaid);
System.exit(0);
System.out.println("In
main().");
}//close main() function
//Defining
a function
public
String DoStuff()
{
return "Doing stuff. Here's
a string!";
}//close main() function
}//close
AFunction class |
Notice: Here we
define a function under main(), "DoStuff()" and invoke it from within
main().
Example 3 - No return value,
takes 1 argument:
import
javax.swing.*;
public
class
DaFunkShen
{
public
void main(String[] args)
{
String WhatWasSaid = "";
System.out.println("In main().");
DoStuff("Passed to
function as a String.");
System.exit(0);
System.out.println("In
main().");
}//close main() function
//Defining
a function
public
void DoStuff(String WhatToSay)
{
System.out.println(WhatToSay);
}//close main() function
}//close
AFunction class |
Notice: Here we
define a function under main(), "DoStuff()" and invoke it from within
main().
Example 4 - Returns a value,
takes 2 arguments:
import
javax.swing.*;
public
class
DaFunkShen
{
public
void main(String[] args)
{
String WhatWasSaid = "";
System.out.println("In main().");
WhatWasSaid =
DoStuff(36, "blue");
System.out.println(WhatWasSaid);
System.exit(0);
System.out.println("In
main().");
}//close main() function
//Defining
a function
public String DoStuff(int
x, String y)
{
String Message = "I am" + x + " years old and my " +
"favorite color is " + y + ".\n";
return Message;
}//close main() function
}//close
AFunction class |
Notice: Here we
define a function under main(), "DoStuff()" and invoke it from within
main().
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