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diff --git a/tools/ahat/src/SubsetSelector.java b/tools/ahat/src/SubsetSelector.java
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+++ b/tools/ahat/src/SubsetSelector.java
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+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.ahat;
+
+import java.util.List;
+
+/**
+ * The SubsetSelector is that can be added to a page that lets the
+ * user select a limited number of elements to show.
+ * This is used to limit the number of elements shown on a page by default,
+ * requiring the user to explicitly request more, so users not interested in
+ * more don't have to wait for everything to render.
+ */
+class SubsetSelector<T> {
+  private static final int kIncrAmount = 1000;
+  private static final int kDefaultShown = 1000;
+
+  private Query mQuery;
+  private String mId;
+  private int mLimit;
+  private List<T> mElements;
+
+  /**
+   * @param id - the name of the query parameter key that should hold
+   * the limit selectors selected value.
+   * @param query - The query for the current page. This is required so the
+   * LimitSelector can add a link to the same page with modified limit
+   * selection.
+   * @param elements - the elements to select from. The collection of elements
+   * should not be modified during the lifetime of the SubsetSelector object.
+   */
+  public SubsetSelector(Query query, String id, List<T> elements) {
+    mQuery = query;
+    mId = id;
+    mLimit = getSelectedLimit(query, id, elements.size());
+    mElements = elements;
+  }
+
+  // Return the list of elements included in the selected subset.
+  public List<T> selected() {
+    return mElements.subList(0, mLimit);
+  }
+
+  // Return the list of remaining elements not included in the selected subset.
+  public List<T> remaining() {
+    return mElements.subList(mLimit, mElements.size());
+  }
+
+  /**
+   * Returns the currently selected limit.
+   * @param query the current page query
+   * @param size the total number of elements to select from
+   * @return the number of selected elements
+   */
+  private static int getSelectedLimit(Query query, String id, int size) {
+    String value = query.get(id, null);
+    try {
+      int ivalue = Math.min(size, Integer.parseInt(value));
+      return Math.max(0, ivalue);
+    } catch (NumberFormatException e) {
+      // We can't parse the value as a number. Ignore it.
+    }
+    return Math.min(kDefaultShown, size);
+  }
+
+  // Render the limit selector to the given doc.
+  // It has the form:
+  //  (showing X of Y - show none - show less - show more - show all)
+  public void render(Doc doc) {
+    int all = mElements.size();
+    if (all > kDefaultShown) {
+      DocString menu = new DocString();
+      menu.appendFormat("(%d of %d elements shown - ", mLimit, all);
+      if (mLimit > 0) {
+        int less = Math.max(0, mLimit - kIncrAmount);
+        menu.appendLink(mQuery.with(mId, 0), DocString.text("show none"));
+        menu.append(" - ");
+        menu.appendLink(mQuery.with(mId, less), DocString.text("show less"));
+        menu.append(" - ");
+      } else {
+        menu.append("show none - show less - ");
+      }
+      if (mLimit < all) {
+        int more = Math.min(mLimit + kIncrAmount, all);
+        menu.appendLink(mQuery.with(mId, more), DocString.text("show more"));
+        menu.append(" - ");
+        menu.appendLink(mQuery.with(mId, all), DocString.text("show all"));
+        menu.append(")");
+      } else {
+        menu.append("show more - show all)");
+      }
+      doc.println(menu);
+    }
+  }
+}