Use fully qualified java.lang.Object in protoc java code.

java/src/test/java/com/google/protobuf/test_bad_identifiers.proto

@@ -60,6 +60,10 @@ message Override {
   optional int32 override = 1;
 }
 
+message Object {
+  optional int32 object = 1;
+}
+
 service TestConflictingMethodNames {
   rpc Override(TestMessage) returns (TestMessage);
 }

src/google/protobuf/compiler/java/java_message.cc

@@ -550,7 +550,8 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
 
   printer->Print(
     "@java.lang.Override\n"
-    "protected Object writeReplace() throws java.io.ObjectStreamException {\n"
+    "protected java.lang.Object writeReplace()\n"
+    "    throws java.io.ObjectStreamException {\n"
     "  return super.writeReplace();\n"
     "}\n"
     "\n");
@@ -1182,7 +1183,7 @@ void MessageGenerator::GenerateIsInitialized(
 void MessageGenerator::GenerateEqualsAndHashCode(io::Printer* printer) {
   printer->Print(
     "@java.lang.Override\n"
-    "public boolean equals(final Object obj) {\n");
+    "public boolean equals(final java.lang.Object obj) {\n");
   printer->Indent();
   printer->Print(
     "if (obj == this) {\n"

src/google/protobuf/compiler/java/java_string_field.cc

@@ -168,14 +168,14 @@ GenerateInterfaceMembers(io::Printer* printer) const {
 void StringFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
-    "private Object $name$_;\n"
+    "private java.lang.Object $name$_;\n"
     "$deprecation$public boolean has$capitalized_name$() {\n"
     "  return $get_has_field_bit_message$;\n"
     "}\n");
 
   printer->Print(variables_,
     "$deprecation$public String get$capitalized_name$() {\n"
-    "  Object ref = $name$_;\n"
+    "  java.lang.Object ref = $name$_;\n"
     "  if (ref instanceof String) {\n"
     "    return (String) ref;\n"
     "  } else {\n"
@@ -189,7 +189,7 @@ GenerateMembers(io::Printer* printer) const {
     "  }\n"
     "}\n"
     "private com.google.protobuf.ByteString get$capitalized_name$Bytes() {\n"
-    "  Object ref = $name$_;\n"
+    "  java.lang.Object ref = $name$_;\n"
     "  if (ref instanceof String) {\n"
     "    com.google.protobuf.ByteString b = \n"
     "        com.google.protobuf.ByteString.copyFromUtf8((String) ref);\n"
@@ -204,14 +204,14 @@ GenerateMembers(io::Printer* printer) const {
 void StringFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
-    "private Object $name$_ $default_init$;\n"
+    "private java.lang.Object $name$_ $default_init$;\n"
     "$deprecation$public boolean has$capitalized_name$() {\n"
     "  return $get_has_field_bit_builder$;\n"
     "}\n");
 
   printer->Print(variables_,
     "$deprecation$public String get$capitalized_name$() {\n"
-    "  Object ref = $name$_;\n"
+    "  java.lang.Object ref = $name$_;\n"
     "  if (!(ref instanceof String)) {\n"
     "    String s = ((com.google.protobuf.ByteString) ref).toStringUtf8();\n"
     "    $name$_ = s;\n"