Merge "Switch ReferenceWithHistory to use ArrayDeque" (3bb222aa) · Commits · e / os / android_frameworks_base

services/core/java/com/android/server/timezonedetector/ReferenceWithHistory.java

+47 −12

Original line number	Diff line number	Diff line
		@@ -22,7 +22,7 @@ import android.annotation.Nullable;

		import com.android.internal.util.IndentingPrintWriter;

		import java.util.LinkedList;
		import java.util.ArrayDeque;

		/**
		* A class that behaves like the following definition, except it stores the history of values set
		@@ -50,11 +50,18 @@ import java.util.LinkedList;
		*/
		public final class ReferenceWithHistory<V> {

		/** The size the history linked list is allowed to grow to. */
		private static final Object NULL_MARKER = "{null marker}";

		/** The maximum number of references to store. */
		private final int mMaxHistorySize;

		/**
		* The history storage. Note that ArrayDeque doesn't support {@code null} so this stores Object
		* and not V. Use {@link #packNullIfRequired(Object)} and {@link #unpackNullIfRequired(Object)}
		* to convert to / from the storage object.
		*/
		@Nullable
		private LinkedList<V> mValues;
		private ArrayDeque<Object> mValues;

		/**
		* Creates an instance that records, at most, the specified number of values.
		@@ -69,22 +76,31 @@ public final class ReferenceWithHistory<V> {
		/** Returns the current value, or {@code null} if it has never been set. */
		@Nullable
		public V get() {
		return (mValues == null \|\| mValues.isEmpty()) ? null : mValues.getFirst();
		if (mValues == null \|\| mValues.isEmpty()) {
		return null;
		}
		Object value = mValues.getFirst();
		return unpackNullIfRequired(value);
		}

		/** Sets the current value. Returns the previous value, or {@code null}. */
		/**
		* Sets the current value. Returns the previous value, which can be {@code null} if the
		* reference has never been set, or if the reference has been set to {@code null}.
		*/
		@Nullable
		public V set(@Nullable V newValue) {
		if (mValues == null) {
		mValues = new LinkedList<>();
		mValues = new ArrayDeque<>(mMaxHistorySize);
		}

		V previous = get();

		mValues.addFirst(newValue);
		if (mValues.size() > mMaxHistorySize) {
		if (mValues.size() >= mMaxHistorySize) {
		mValues.removeLast();
		}

		V previous = get();

		Object nullSafeValue = packNullIfRequired(newValue);
		mValues.addFirst(nullSafeValue);
		return previous;
		}

		@@ -96,8 +112,8 @@ public final class ReferenceWithHistory<V> {
		ipw.println("{Empty}");
		} else {
		int i = 0;
		for (V value : mValues) {
		ipw.println(i + ": " + value);
		for (Object value : mValues) {
		ipw.println(i + ": " + unpackNullIfRequired(value));
		i++;
		}
		}
		@@ -115,4 +131,23 @@ public final class ReferenceWithHistory<V> {
		public String toString() {
		return String.valueOf(get());
		}

		/**
		* Turns a non-nullable Object into a nullable value. See also
		* {@link #packNullIfRequired(Object)}.
		*/
		@SuppressWarnings("unchecked")
		@Nullable
		private V unpackNullIfRequired(@NonNull Object value) {
		return value == NULL_MARKER ? null : (V) value;
		}

		/**
		* Turns a nullable value into a non-nullable Object. See also
		* {@link #unpackNullIfRequired(Object)}.
		*/
		@NonNull
		private Object packNullIfRequired(@Nullable V value) {
		return value == null ? NULL_MARKER : value;
		}
		}