--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/dancres/blitz/entry/SortingLocator.java	Sat Mar 21 11:00:06 2009 +0000
@@ -0,0 +1,94 @@
+package org.dancres.blitz.entry;
+
+import java.io.IOException;
+
+import org.dancres.blitz.oid.OID;
+
+/**
+   This locator will provide a single FIFO list of tuples created from
+   merging the contents of all the passed locators.  It assumes that each
+   individual locator is FIFO sorted.
+ */
+class SortingLocator implements TupleLocator {
+    private TupleLocator[] theLocators;
+
+    private OID[] theSortBuffer;
+
+    private OID theNext;
+
+    SortingLocator(TupleLocator[] aSetOfLocators) {
+        theLocators = aSetOfLocators;
+    }
+
+    /**
+       Invoke this to load the next matching Tuple.
+
+       @return <code>true</code> if there was a tuple, <code>false</code>
+       otherwise
+     */
+    public boolean fetchNext() throws IOException {
+        if (theSortBuffer == null) {
+            // First-time init
+            theSortBuffer = new OID[theLocators.length];
+
+            for (int i = 0; i < theLocators.length; i++) {
+                boolean hasUID = theLocators[i].fetchNext();
+
+                if (hasUID)
+                    theSortBuffer[i] = theLocators[i].getOID();
+            }
+        } else {
+            // This cannot be the first time so if theNext is null, we've
+            // run out of matches
+            if (theNext == null)
+                return false;
+
+            // Refresh slots in the slot buffer which contain the last OID
+            for (int i = 0; i < theSortBuffer.length; i++) {
+                if (theSortBuffer[i] != null) {
+                    if (theSortBuffer[i].equals(theNext)) {
+                        if (theLocators[i].fetchNext())
+                            theSortBuffer[i] = theLocators[i].getOID();
+                        else
+                            theSortBuffer[i] = null;
+                    }
+                }
+            }
+        }
+
+        OID myOldest = null;
+
+        for (int i = 0; i < theSortBuffer.length; i++) {
+            if (theSortBuffer[i] != null) {
+                if (myOldest == null) {
+                    myOldest = theSortBuffer[i];
+                } else {
+                    if (theSortBuffer[i].compareTo(myOldest) < 0) {
+                        myOldest = theSortBuffer[i];
+                    }
+                }
+            }
+        }
+
+        theNext = myOldest;
+
+        return (theNext != null);
+    }
+
+    /**
+       @return the OID of the tuple just fetched with
+       <code>fetchNext</code>
+     */
+    public OID getOID() {
+        return theNext;
+    }
+
+    /**
+       When you've finished with the TupleLocator instance, call release.
+     */
+    public void release() throws IOException {
+        for (int i = 0; i < theLocators.length; i++) {
+            theLocators[i].release();
+        }
+    }
+}
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