Android: Add a java version of ObserverList.

base/android/javatests/src/org/chromium/base/ObserverListTest.java

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.base;
+
+import android.test.InstrumentationTestCase;
+import android.test.suitebuilder.annotation.SmallTest;
+
+import org.chromium.base.test.util.Feature;
+
+import java.lang.Iterable;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+/**
+ * Tests for (@link ObserverList}.
+ */
+public class ObserverListTest extends InstrumentationTestCase {
+    interface Observer {
+        void observe(int x);
+    }
+
+    private static class Foo implements Observer {
+        private final int mScalar;
+        private int mTotal = 0;
+
+        Foo(int scalar) {
+            mScalar = scalar;
+        }
+
+        @Override
+        public void observe(int x) {
+            mTotal += x * mScalar;
+        }
+    }
+
+    /**
+     * An observer which removes a given Observer object from the list when observe is called.
+     */
+    private static class FooRemover implements Observer {
+        private final ObserverList<Observer> mList;
+        private final Observer mDoomed;
+
+        FooRemover(ObserverList<Observer> list, Observer innocent) {
+            mList = list;
+            mDoomed = innocent;
+        }
+
+        @Override
+        public void observe(int x) {
+            mList.removeObserver(mDoomed);
+        }
+    }
+
+    private static <T> int getSizeOfIterable(Iterable<T> iterable) {
+        int num = 0;
+        for (T el : iterable)
+            num++;
+        return num;
+    }
+
+    @SmallTest
+    @Feature({"Android-AppBase"})
+    public void testRemoveWhileIteration() {

[bulach, 2013/02/28 12:39:12]

it'd be nice to add a "testAddWhileIterating" and ensure that the new iterator
is NOT called, wdyt?

[nilesh, 2013/02/28 19:35:36]

Makes sense, add a test for addWhileIterating.

+        ObserverList<Observer> observerList = new ObserverList<Observer>();
+        Foo a, b, c, d, e;

[bulach, 2013/02/28 12:39:12]

nit: I don't think this is strictly forbidden, but just in case, it may be
simpler to remove the multiple declaration and just repeat:
Foo a = new Foo(1);
Foo b = ...

[nilesh, 2013/02/28 19:35:36]

Done.

+        a = new Foo(1);
+        b = new Foo(-1);
+        c = new Foo(1);
+        d = new Foo(-1);
+        e = new Foo(-1);
+        FooRemover evil = new FooRemover(observerList, c);
+
+        observerList.addObserver(a);
+        observerList.addObserver(b);
+
+        for (Observer obs : observerList)
+            obs.observe(10);
+
+        // Removing an observer not in the list should do nothing.
+        observerList.removeObserver(e);
+
+        observerList.addObserver(evil);
+        observerList.addObserver(c);
+        observerList.addObserver(d);
+
+        for (Observer obs : observerList)
+            obs.observe(10);
+
+        // observe should be called twice on a.
+        assertEquals(20, a.mTotal);
+        // observe should be called twice on b.
+        assertEquals(-20, b.mTotal);
+        // evil removed c from the observerList before it got any callbacks.
+        assertEquals(0, c.mTotal);
+        // observe should be called once on d.
+        assertEquals(-10, d.mTotal);
+        // e was never added to the list, observe should not be called.
+        assertEquals(0, e.mTotal);
+    }
+
+    @SmallTest
+    @Feature({"Android-AppBase"})
+    public void testIterator() {
+        ObserverList<Integer> observerList = new ObserverList<Integer>();
+        observerList.addObserver(5);
+        observerList.addObserver(10);
+        observerList.addObserver(15);
+        assertEquals(3, getSizeOfIterable(observerList));
+
+        observerList.removeObserver(10);
+        assertEquals(2, getSizeOfIterable(observerList));
+
+        Iterator<Integer> it = observerList.iterator();
+        assertTrue(it.hasNext());
+        assertTrue(5 == it.next());
+        assertTrue(it.hasNext());
+        assertTrue(15 == it.next());
+        assertFalse(it.hasNext());
+
+        boolean removeExceptionThrown = false;
+        try {
+            it.remove();
+            fail("Expecting UnsupportedOperationException to be thrown here.");
+        } catch (UnsupportedOperationException e) {
+            removeExceptionThrown = true;
+        }
+        assertTrue(removeExceptionThrown);
+        assertEquals(2, getSizeOfIterable(observerList));
+
+        boolean noElementExceptionThrown = false;
+        try {
+            it.next();
+            fail("Expecting NoSuchElementException to be thrown here.");
+        } catch (NoSuchElementException e) {
+            noElementExceptionThrown = true;
+        }
+        assertTrue(noElementExceptionThrown);
+    }
+}