A container for keeping a list of recent objects.

git-svn-id: https://samskivert.googlecode.com/svn/trunk@1032 6335cc39-0255-0410-8fd6-9bcaacd3b74c
2003-01-21 21:46:31 +00:00
parent 2fd74dc829
commit a47caf48cb
1 changed files with 91 additions and 0 deletions
@@ -0,0 +1,91 @@
+//
+// $Id: RecentList.java,v 1.1 2003/01/21 21:46:31 mdb Exp $
+
+package com.samskivert.util;
+
+import java.util.Arrays;
+
+/**
+ * An array list that maintains a list of the N most recent entries added
+ * to it.
+ */
+public class RecentList
+{
+    /**
+     * Constructs a recent list that keeps the specified number of most
+     * recently added objects.
+     */
+    public RecentList (int keepCount)
+    {
+        _list = new Object[keepCount];
+    }
+
+    /**
+     * Returns the number of elements in this list.
+     */
+    public int size ()
+    {
+        return Math.min(_lastPos, _list.length);
+    }
+
+    /**
+     * Clears the list.
+     */
+    public void clear ()
+    {
+        Arrays.fill(_list, null);
+        _lastPos = 0;
+    }
+
+    /**
+     * Adds the specified value to the list.
+     */
+    public void add (Object value)
+    {
+        _list[_lastPos++ % _list.length] = value;
+        // keep last pos cycling from keepCount to 2*keepCount-1
+        if (_lastPos == 2*_list.length) {
+            _lastPos = _list.length;
+        }
+    }
+
+    /**
+     * Returns true if the supplied value is equal (using {@link
+     * Object#equals}) to any value in the list.
+     */
+    public boolean contains (Object value)
+    {
+        for (int ii = 0, ll = _list.length; ii < ll; ii++) {
+            if (_list[ii] != null && _list[ii].equals(value)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Gets the Nth most recently added value from the list.
+     * <code>null</code> is returned if the list does not contain at least
+     * <code>index+1</code> entries.
+     */
+    public Object get (int index)
+    {
+        return _list[(_lastPos-index-1+_list.length)%_list.length];
+    }
+
+    public static void main (String[] args)
+    {
+        RecentList list = new RecentList(5);
+        for (int ii = 0; ii < 10; ii++) {
+            list.add(new Integer(ii));
+        }
+        System.out.println("Contains 3 " + list.contains(new Integer(3)));
+        System.out.println("Contains 7 " + list.contains(new Integer(7)));
+        for (int ii = 0; ii < list.size(); ii++) {
+            System.out.println(ii + " => " + list.get(ii));
+        }
+    }
+
+    protected Object[] _list;
+    protected int _lastPos;
+}