Java 天地·Core Java·Lecture Notes·Unitt 3 - Core Java Programming Concepts

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Categories of program statements

The simple program below consists of a single class:TicketDiscount.java. Every Java class is composed of program statements. Some statements, called compound statements are comprised of more than one statement themselves.

class TicketDiscount
{
public static void main( String args[] )
    {
    int age;

     // assign a random age (0 .. 99) to

     // variable 'age'

    age = (int) ( 100 * Math.random() );
    System.out.println("age is: " + age);
    if( age >= 60 )
      {
      System.out.println( age + "is 60 or over" );
      System.out.println("qualifies for discount");
      }
   }
}

There are several different categories of Java program statement. They include input and output statements, statements to change the values of variables, statements to send messages to objects, and statements to determine which statement to execute next. The table below analyses some of the different categories of statement that make up the implementation of the class TicketDiscount.java.Although in this module we have not (yet) introduced each kind of statement, the table should help to illustrate how even a simple Java program consisting of a single class may be made up of many different kinds of statement.

Category of statement	Example of statement from TicketDiscount.java
class declaration	class TicketDiscount { ... }
method declaration	public static void main( String args[] ) { ... }
variable declaration	int age;
comment	// assign a random age (0 .. 99) to // variable 'age'
variable assignment	age = (int) ( 100 * Math.random() );
message sending	System.out.println("age is: " + age);
control	if( age >= 60 ) {...}

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