| Introduction to Java Methods
This tutorial will take you step by step in understanding the basics of a method , how to define it and how to use it. The best way to learn is to compile and run these programs yourself (copy, paste, compile and run !). Comments such as /* this is a comment */ or // this is another comment are inserted to explain what does the line of code do. The programs are kept simple for the purpose of concentrating on the main idea in question. Example 1: method that calculates and displays a volume
class Room1{
double length;
double width;
double height;
// this defines a method called volume that calculates and displays the volume
// of a given object whose instance variables are length, width and height.
// IMPORTANT: the instance variables length, height and width are
// referred to directly inside the method volume .
void volume(){
double vol = length*width*height;
System.out.println("volume of this room is = "+vol);
}
public static void main(String t[]){
Room1 myroom1 = new Room1(); // creates object myroom1
Room1 myroom2 = new Room1(); // creates object myroom2
myroom1.length= 10.0; // assigns values to instance
myroom1.width = 8.0; // variables of myroom1
myroom1.height = 5.5;
myroom2.length= 9.0; // assigns values to instance
myroom2.width = 7.0; // variables of myroom2
myroom2.height = 4.5;
// this is how you you invoke the volume method on myroom1
myroom1.volume(); // Note the use of the dot (.) operator when invoking
// a method.
// this is how you you invoke the volume method on myroom2
myroom2.volume();
}
}
The above program defines a template for the class Room1,
with instance variables length, height and width and a method called volume
that calculates the volume .
IMPORTANT: the instance variables length, height and width are referred to directly inside the method volume. This is because when we invoke a method we invoke it relative to an object : myroom1.volume(). Example 2: a method that calculates and returns a volume
class Room1{
double length;
double width;
double height;
// this defines a method called volume that calculates the volume
// of a given object and returns it.
double volume(){ // the returned volume is of type double
return length*width*height; // returns the volume.
}
public static void main(String t[]){
Room1 myroom1 = new Room1(); // creates object myroom1
Room1 myroom2 = new Room1(); // creates object myroom2
myroom1.length= 10.0; // assigns values to instance
myroom1.width = 8.0; // variables of myroom1
myroom1.height = 5.5;
myroom2.length= 9.0; // assigns values to instance
myroom2.width = 7.0; // variables of myroom2
myroom2.height = 4.5;
// this is how you you invoke the volume method on myroom1
double vol1 = myroom1.volume();
// displays vol1
System.out.println("volume of myroom1 = "+vol1);
// this is how you you invoke the volume method on myroom2
double vol2 = myroom2.volume();
// displays vol2
System.out.println("volume of myroom2 = "+vol2);
}
}
In example 1 the keyword void was used that is because the
method volume there did not return anything.
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