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.


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Comments syntax:

// Line-oriented.




can span several lines.


Class definition syntax: […] means optional.

[public] class class-name [inheritance-specification]







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: ");


((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])




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]




A return type void means the method does not return any value.

param-list looks like:

type1 param1, type2 param2, …, typeN paramN