The collections api - Data Structures and Problem Solving Using Java - page 269

1 /**
2 * Test program for HashSet.
3 */
4 class IteratorTest
5 {
6 public static void main( String [ ] args )
7 {
8 List<SimpleStudent> stud1 = new ArrayList<SimpleStudent>( );
9 stud1.add( new SimpleStudent( "Bob", 0 ) );
10 stud1.add( new SimpleStudent( "Joe", 1 ) );
11 stud1.add( new SimpleStudent( "Bob", 2 ) ); // duplicate
12
13 // Will only have 2 items, if hashCode is
14 // implemented. Otherwise will have 3 because
15 // duplicate will not be detected.
16 Set<SimpleStudent> stud2 = new HashSet<SimpleStudent>( stud1 );
17
18 printCollection( stud1 ); // Bob Joe Bob (unspecified order)
19 printCollection( stud2 ); // Two items in unspecified order
20 }
21 }
22
23 /**
24 * Illustrates use of hashCode/equals for a user-defined class.
25 * Students are ordered on basis of name only.
26 */
27 class SimpleStudent implements Comparable<SimpleStudent>
28 {
29 String name;
30 int id;
31
32 public SimpleStudent( String n, int i )
33 { name = n; id = i; }
34
35 public String toString( )
36 { return name + " " + id; }
37
38 public boolean equals( Object rhs )
39 {
40 if( rhs == null || getClass( ) != rhs.getClass( ) )
41 return false;
42
43 SimpleStudent other = (SimpleStudent) rhs;
44 return name.equals( other.name );
45 }
46
47 public int hashCode( )
48 { return name.hashCode( ); }
49 }
figure 6.35
Illustrates the equals and hashCode methods for use in HashSet