COMP 212 -Summary of Java Syntax
A Java program consists of one or more classes one of them must be public and must have a method with the following signature:
public static void main (String[] args)
.Basically, the
main method will instantiate appropriate objects and send them "messages" (by calling their methods) to perform the desired tasks.
Comments syntax:
// Line-oriented
.
/*
block-oriented
can span several lines.
*/
Class definition syntax: […] means optional.
[public] class class-name [inheritance-specification]
{
[field-list;]
[constructor-list;]
[method-list;]
}
Examples:
public class PizzaClient
{
public static void main (String[] args)
{
// instantiation and assignment.
Pizza cirPizza
= new Pizza (4.69, new Circle (2.5));
Pizza rectPizza
= new Pizza (4.49, new Rectangle (5, 4));
// output to standard output stream.
System.out.println (cirPizza);
System.out.println (rectPizza);
System.out.print ("Round Pizza is a better deal than Rectangular Pizza: ");
System.out.println
((cirPizza.dPrice () / cirPizza.dArea () < rectPizza.dPrice () / rectPizza.dArea ()));
// NOTE: infix notation for arithmetic expressions, and
// "dot" notation for method calls.
}
}
NOTE: Each Java statement must terminate with a semi-colon.
public class
Rectangle extends AShape{
private double _height; // Note the underscore.
private double _width;
public Rectangle (double width, double height)
{
_height = height;
_width = width;
// the underscore helps distinguish the field from the // parameter.
}
public double getArea()
{
return _height * _width; // infix notation!
}
public String toString ()
{
return "Rectangle (width = " + _width + ", heigth = " + _height + ")";
}
}
Field list syntax: A field list consists of zero or more field declarations of the form
[static] [final] [public | private | protected]
field-type field-name [assignment];
Constructor list syntax: A constructor list consists of zero or more constructor definitions of the form
[public | private | protected]
class-name ([parameter-list])
{
[statement-list;]
}
NOTE: The constructor's name is the same as the class name. Constructors are used for initialization of the object during the object's instantiation only.
Method list syntax: A method list consists of zero or more method definitions of the form
[static] [final] [public | private | protected]
return-type method-name [param-list]
{
[statement-list;]
}
A return type
void means the method does not return any value.param-list
looks like:type1 param1, type2 param2, …, typeN paramN