Add ComponentName.createRelative methods

In a number of places, it's convenient to be able to refer to
ComponentName classes with relative package paths as they are
interpreted in manifest parsing. Express the official (yet simple)
policy for this in a simple pair of factory methods for ComponentName.

Change-Id: I81a40c81b7975445dd9f06292363b69bb072b16d

api/current.txt

@@ -7260,6 +7260,8 @@ package android.content {
     ctor public ComponentName(android.os.Parcel);
     method public android.content.ComponentName clone();
     method public int compareTo(android.content.ComponentName);
+    method public static android.content.ComponentName createRelative(java.lang.String, java.lang.String);
+    method public static android.content.ComponentName createRelative(android.content.Context, java.lang.String);
     method public int describeContents();
     method public java.lang.String flattenToShortString();
     method public java.lang.String flattenToString();

api/system-current.txt

@@ -7474,6 +7474,8 @@ package android.content {
     ctor public ComponentName(android.os.Parcel);
     method public android.content.ComponentName clone();
     method public int compareTo(android.content.ComponentName);
+    method public static android.content.ComponentName createRelative(java.lang.String, java.lang.String);
+    method public static android.content.ComponentName createRelative(android.content.Context, java.lang.String);
     method public int describeContents();
     method public java.lang.String flattenToShortString();
     method public java.lang.String flattenToString();

core/java/android/content/ComponentName.java

@@ -18,6 +18,7 @@ package android.content;
 
 import android.os.Parcel;
 import android.os.Parcelable;
+import android.text.TextUtils;
 
 import java.io.PrintWriter;
 import java.lang.Comparable;
@@ -36,6 +37,56 @@ public final class ComponentName implements Parcelable, Cloneable, Comparable<Co
     private final String mPackage;
     private final String mClass;
 
+    /**
+     * Create a new component identifier where the class name may be specified
+     * as either absolute or relative to the containing package.
+     *
+     * <p>Relative package names begin with a <code>'.'</code> character. For a package
+     * <code>"com.example"</code> and class name <code>".app.MyActivity"</code> this method
+     * will return a ComponentName with the package <code>"com.example"</code>and class name
+     * <code>"com.example.app.MyActivity"</code>. Fully qualified class names are also
+     * permitted.</p>
+     *
+     * @param pkg the name of the package the component exists in
+     * @param cls the name of the class inside of <var>pkg</var> that implements
+     *            the component
+     * @return the new ComponentName
+     */
+    public static ComponentName createRelative(String pkg, String cls) {
+        if (TextUtils.isEmpty(cls)) {
+            throw new IllegalArgumentException("class name cannot be empty");
+        }
+
+        final String fullName;
+        if (cls.charAt(0) == '.') {
+            // Relative to the package. Prepend the package name.
+            fullName = pkg + cls;
+        } else {
+            // Fully qualified package name.
+            fullName = cls;
+        }
+        return new ComponentName(pkg, fullName);
+    }
+
+    /**
+     * Create a new component identifier where the class name may be specified
+     * as either absolute or relative to the containing package.
+     *
+     * <p>Relative package names begin with a <code>'.'</code> character. For a package
+     * <code>"com.example"</code> and class name <code>".app.MyActivity"</code> this method
+     * will return a ComponentName with the package <code>"com.example"</code>and class name
+     * <code>"com.example.app.MyActivity"</code>. Fully qualified class names are also
+     * permitted.</p>
+     *
+     * @param pkg a Context for the package implementing the component
+     * @param cls the name of the class inside of <var>pkg</var> that implements
+     *            the component
+     * @return the new ComponentName
+     */
+    public static ComponentName createRelative(Context pkg, String cls) {
+        return createRelative(pkg.getPackageName(), cls);
+    }
+
     /**
      * Create a new component identifier.
      *