1	// Example 3.1 joi/examples/StaticDemo.java
     2	//
     3	//
     4	// Copyright 2003 Bill Campbell and Ethan Bolker
     5	
     6	// Demonstrate the interplay between static members (fields and methods)
     7	// and instance (non-static) members.
     8	//
     9	// %> java StaticDemo
    10	// 0: counter = 1; objectField = 0
    11	// StaticDemo.classMethod() = 100
    12	// classMethod() = 100
    13	// 1: counter = 2; objectField = 1
    14	// StaticDemo.classMethod() = 101
    15	// classMethod() = 101
    16	// 2: counter = 3; objectField = 2
    17	// StaticDemo.classMethod() = 103
    18	// classMethod() = 103
    19	// 3: counter = 4; objectField = 3
    20	// StaticDemo.classMethod() = 106
    21	// classMethod() = 106
    22	// 4: counter = 5; objectField = 4
    23	// StaticDemo.classMethod() = 110
    24	// classMethod() = 110
    25	//
    26	// last classMethod() = 110
    27	
    28	public class StaticDemo
    29	{
    30	    // Declare three (static) class variables
    31	    // A class variable is associated with the (one) class.
    32	
    33	    private static int counter  = 0; 
    34	    private static int classVar = 0; 
    35	    private static Terminal terminal = new Terminal(); 
    36	
    37	    int objectField = 0;     // an instance variable; one per object
    38	
    39	    // The constructor keeps track of how many StaticDemo objects
    40	    // have been constructed.
    41	
    42	    public StaticDemo( int objectFieldValue )
    43	    {
    44	        objectField = objectFieldValue; // set the instance variable
    45	        counter++;  // increment counter (counting the StaicDemos made)
    46	    }
    47	
    48	    public void instanceMethod()
    49	    {
    50	        // Instance methods can refer to both instance variables
    51	        // and class variables.
    52	        
    53	        terminal.println( "counter = " + counter + 
    54	                          "; objectField = " + objectField );
    55	        classVar = classVar + objectField;
    56	
    57	    }
    58	
    59	    public static int classMethod()
    60	    {
    61	        // Class methods may refer only to class variables 
    62	        // (and other class methods), as well as to local variables.
    63	
    64	        // What happens if we comment out the next line?
    65	        int counter = 100;
    66	        
    67	        return counter + classVar;
    68	    }
    69	
    70	    public static void main( String[] args )
    71	    {
    72	        for (int i = 0; i < 5; i++) {
    73	            StaticDemo sd = new StaticDemo( i );
    74	            terminal.print( i + ": " );
    75	            sd.instanceMethod();
    76	
    77	            // classMethod()
    78	            //   is equivalent to
    79	            // StaticDemo.classMethod()
    80	            terminal.println( "StaticDemo.classMethod() = " 
    81	                              + StaticDemo.classMethod() );
    82	            terminal.println( "classMethod() = " 
    83	                              + classMethod() );
    84	        }
    85	        terminal.println();
    86	        terminal.println( "last classMethod() = " + classMethod() );
    87	    }
    88	}