Disable overriding methods in final classes. (#626)

2 files changed, 23 insertions, 0 deletions

diff --git a/src/main/java/com/squareup/javapoet/MethodSpec.java b/src/main/java/com/squareup/javapoet/MethodSpec.java
index eff5410..67a7fb2 100644
--- a/src/main/java/com/squareup/javapoet/MethodSpec.java
+++ b/src/main/java/com/squareup/javapoet/MethodSpec.java
@@ -25,6 +25,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import javax.lang.model.SourceVersion;
+import javax.lang.model.element.Element;
 import javax.lang.model.element.ExecutableElement;
 import javax.lang.model.element.Modifier;
 import javax.lang.model.element.TypeParameterElement;
@@ -188,6 +189,11 @@ public final class MethodSpec {
   public static Builder overriding(ExecutableElement method) {
     checkNotNull(method, "method == null");
 
+    Element enclosingClass = method.getEnclosingElement();
+    if (enclosingClass.getModifiers().contains(Modifier.FINAL)) {
+      throw new IllegalArgumentException("Cannot override method on final class " + enclosingClass);
+    }
+
     Set<Modifier> modifiers = method.getModifiers();
     if (modifiers.contains(Modifier.PRIVATE)
         || modifiers.contains(Modifier.FINAL)
diff --git a/src/test/java/com/squareup/javapoet/MethodSpecTest.java b/src/test/java/com/squareup/javapoet/MethodSpecTest.java
index 96923eb..334a6ae 100644
--- a/src/test/java/com/squareup/javapoet/MethodSpecTest.java
+++ b/src/test/java/com/squareup/javapoet/MethodSpecTest.java
@@ -123,6 +123,11 @@ public final class MethodSpecTest {
   interface ExtendsIterableWithDefaultMethods extends Iterable<Object> {
   }
 
+  final class FinalClass {
+    void method() {
+    }
+  }
+
   @Test public void overrideEverything() {
     TypeElement classElement = getElement(Everything.class);
     ExecutableElement methodElement = getOnlyElement(methodsIn(classElement.getEnclosedElements()));
@@ -177,6 +182,18 @@ public final class MethodSpecTest {
         + "}\n");
   }
 
+  @Test public void overrideFinalClassMethod() {
+    TypeElement classElement = getElement(FinalClass.class);
+    List<ExecutableElement> methods = methodsIn(elements.getAllMembers(classElement));
+    try {
+      MethodSpec.overriding(findFirst(methods, "method"));
+      fail();
+    } catch (IllegalArgumentException expected) {
+      assertThat(expected).hasMessageThat().isEqualTo(
+          "Cannot override method on final class com.squareup.javapoet.MethodSpecTest.FinalClass");
+    }
+  }
+
   @Test public void overrideInvalidModifiers() {
     ExecutableElement method = mock(ExecutableElement.class);
     when(method.getModifiers()).thenReturn(ImmutableSet.of(Modifier.FINAL));