Improve the performance of the TypeRewriter.rewrite method

2 files changed, 36 insertions, 3 deletions

diff --git a/dexlib2/src/main/java/org/jf/dexlib2/rewriter/TypeRewriter.java b/dexlib2/src/main/java/org/jf/dexlib2/rewriter/TypeRewriter.java
index 862111fc..252003c5 100644
--- a/dexlib2/src/main/java/org/jf/dexlib2/rewriter/TypeRewriter.java
+++ b/dexlib2/src/main/java/org/jf/dexlib2/rewriter/TypeRewriter.java
@@ -36,12 +36,20 @@ import javax.annotation.Nonnull;
 public class TypeRewriter implements Rewriter<String> {
     @Nonnull @Override public String rewrite(@Nonnull String value) {
         if (value.length() > 0 && value.charAt(0) == '[') {
-            int dimensions = value.lastIndexOf("[") + 1;
+            int dimensions = 0;
+            while (value.charAt(dimensions) == '[') {
+                dimensions++;
+            }
 
-            String arraySpecifiers = value.substring(0, dimensions);
             String unwrappedType = value.substring(dimensions);
             String rewrittenType = rewriteUnwrappedType(unwrappedType);
-            return arraySpecifiers + rewrittenType;
+
+            // instance equality, to avoid a value comparison in the common case of the type being unmodified
+            if (unwrappedType != rewrittenType) {
+                return new StringBuilder(dimensions + rewrittenType.length())
+                        .append(value, 0, dimensions).append(rewrittenType).toString();
+            }
+            return value;
         } else {
             return rewriteUnwrappedType(value);
         }
diff --git a/dexlib2/src/test/java/org/jf/dexlib2/rewriter/RewriteArrayTypeTest.java b/dexlib2/src/test/java/org/jf/dexlib2/rewriter/RewriteArrayTypeTest.java
index c8b8d7fb..ab5f7da9 100644
--- a/dexlib2/src/test/java/org/jf/dexlib2/rewriter/RewriteArrayTypeTest.java
+++ b/dexlib2/src/test/java/org/jf/dexlib2/rewriter/RewriteArrayTypeTest.java
@@ -80,4 +80,29 @@ public class RewriteArrayTypeTest {
         Assert.assertEquals(rewrittenClassDef.getType(), "Lcls2;");
         Assert.assertEquals(rewrittenMethodDef.getParameterTypes().get(0), "[[[Lcls2;");
     }
+
+    @Test
+    public void testUnmodifiedArrayTypeTest() {
+        ClassDef class1 = new ImmutableClassDef("Lcls1;", AccessFlags.PUBLIC.getValue(), "Ljava/lang/Object;", null, null,
+                Lists.newArrayList(new ImmutableAnnotation(AnnotationVisibility.RUNTIME, "Lannotation;", null)),
+                Lists.<Field>newArrayList(
+                        new ImmutableField("Lcls1;", "field1", "I", AccessFlags.PUBLIC.getValue(), null, null, null)
+                ),
+                Lists.<Method>newArrayList(
+                        new ImmutableMethod("Lcls1", "method1",
+                                Lists.<MethodParameter>newArrayList(new ImmutableMethodParameter("[[[Lcls1;", null, null)), "V",
+                                AccessFlags.PUBLIC.getValue(), null, null, null)));
+
+        ImmutableDexFile dexFile = new ImmutableDexFile(Opcodes.getDefault(), ImmutableSet.of(class1));
+
+        DexRewriter rewriter = new DexRewriter(new RewriterModule());
+
+        DexFile rewrittenDexFile = rewriter.getDexFileRewriter().rewrite(dexFile);
+
+        ClassDef rewrittenClassDef = Lists.newArrayList(rewrittenDexFile.getClasses()).get(0);
+        Method rewrittenMethodDef = Lists.newArrayList(rewrittenClassDef.getMethods()).get(0);
+
+        Assert.assertEquals(rewrittenClassDef.getType(), "Lcls1;");
+        Assert.assertEquals(rewrittenMethodDef.getParameterTypes().get(0), "[[[Lcls1;");
+    }
 }