ColumnIterator


1   package jimm.datavision.source;
2   import java.util.Iterator  ;
3   import java.util.NoSuchElementException  ;
4   
5   /**
6    * An iterator over the columns in a list of tables. Not used by all data
7    * sources.
8    */
9   public class ColumnIterator implements Iterator   {
10  
11  Iterator   tableIter;
12  Table table;
13  Iterator   colIter;
14  Object   nextCol;
15  
16  /**
17   * Constructor.
18   */
19  public ColumnIterator(Iterator   tableIter) {
20      this.tableIter = tableIter;
21      findNext();
22  }
23  
24  public boolean hasNext() {
25      return nextCol != null;
26  }
27  
28  public Object   next() throws NoSuchElementException   {
29      if (nextCol == null)
30      throw new NoSuchElementException  ();
31  
32      Object   returnValue = nextCol;
33      findNext();         // Fill nextCol for next time
34      return returnValue;
35  }
36  
37  public void remove() throws UnsupportedOperationException   {
38      throw new UnsupportedOperationException  ();
39  }
40  
41  /**
42   * Sets <var>col</var> to the next available column. If there is none,
43   * <var>col</var> will be set to <code>null</code>.
44   */
45  protected void findNext() {
46      nextCol = null;
47  
48      if (colIter == null) {  // First time through
49      if (!tableIter.hasNext()) // No more tables
50          return;     // nextCol will be null
51      table = (Table)tableIter.next();
52      colIter = table.columns();
53      }
54  
55      while (!colIter.hasNext()) {
56      if (!tableIter.hasNext()) // No more tables
57          return;     // nextCol will be null
58      table = (Table)tableIter.next();
59      colIter = table.columns();
60      }
61  
62      nextCol = (Column)colIter.next();
63  }
64  
65  }
66

A to Z: JavaDoc & Examples Daily Java News & Articles Open Source Projects Open Source Codes Free Computer Books Remove Frame

Popular Tags