start java

rootfs_overlay/lkmc/java/LinkedHashMapCheat.java

@@ -0,0 +1,59 @@
+/*
+# LinkedHashMap
+
+http://docs.oracle.com/javase/7/docs/api/java/util/LinkedHashMap.html
+
+Hash map that is iterable in insertion order.
+
+Application LRU cache:
+
+- https://github.com/haoel/leetcode/pull/90/files
+- http://stackoverflow.com/questions/23772102/lru-cache-in-java-with-generics-and-o1-operations
+
+This is a sub-case of a binary heap: it is efficient
+when every item update makes it either the most recent, or oldest.
+For more general binary heap, the new item can go anywhere.
+
+# removeEldestEntry
+
+Example:
+https://github.com/cirosantilli/haoel-leetcode/commit/ff04930b2dc31f270854e40b560723577c7b49fd
+
+Only acts on `put`, `get` does not update values for us.
+*/
+
+import java.util.LinkedList;
+import java.util.LinkedHashMap;
+import java.util.Iterator;
+
+public class LinkedHashMapCheat {
+    public static void main(String[] args) {
+        LinkedList<Integer> output;
+        LinkedList<Integer> expected;
+        Iterator<Integer> it;
+
+        LinkedHashMap<Integer,Integer> m = new LinkedHashMap<>();
+        assert m.put(2, -2) == null;
+        assert m.put(1, -1) == null;
+        assert m.put(3, -3) == null;
+        output = new LinkedList<>();
+        expected = new LinkedList<>();
+        expected.add(2);
+        expected.add(1);
+        expected.add(3);
+        for (int i : m.keySet())
+            output.add(i);
+        assert output.equals(expected);
+
+        it = m.keySet().iterator();
+        it.next();
+        it.remove();
+        output = new LinkedList<>();
+        expected = new LinkedList<>();
+        expected.add(1);
+        expected.add(3);
+        for (int i : m.keySet())
+            output.add(i);
+        assert output.equals(expected);
+    }
+}