8007574: Provide isFunctionalInterface in javax.lang.model

Reviewed-by: jjg

langtools/src/share/classes/com/sun/tools/javac/model/JavacElements.java

@@ -760,6 +760,16 @@ public class JavacElements implements Elements {
         return names.fromString(cs.toString());
     }
 
+    @Override
+    public boolean isFunctionalInterface(TypeElement element) {
+        if (element.getKind() != ElementKind.INTERFACE)
+            return false;
+        else {
+            TypeSymbol tsym = cast(TypeSymbol.class, element);
+            return types.isFunctionalInterface(tsym);
+        }
+    }
+
     /**
      * Returns the tree node and compilation unit corresponding to this
      * element, or null if they can't be found.

langtools/src/share/classes/javax/lang/model/element/TypeElement.java

@@ -111,7 +111,6 @@ public interface TypeElement extends Element, Parameterizable, QualifiedNameable
      */
     Name getQualifiedName();
 
-
     /**
      * Returns the simple name of this type element.
      *
@@ -152,7 +151,6 @@ public interface TypeElement extends Element, Parameterizable, QualifiedNameable
      */
     List<? extends TypeParameterElement> getTypeParameters();
 
-
     /**
      * Returns the package of a top-level type and returns the
      * immediately lexically enclosing element for a {@linkplain

langtools/src/share/classes/javax/lang/model/util/Elements.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2012, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -249,4 +249,14 @@ public interface Elements {
      * @param cs the character sequence to return as a name
      */
     Name getName(CharSequence cs);
+
+    /**
+     * Returns {@code true} if the type element is a functional interface, {@code false} otherwise.
+     *
+     * @param type the type element being examined
+     * @return {@code true} if the element is a functional interface, {@code false} otherwise
+     * @jls 9.8 Functional Interfaces
+     * @since 1.8
+     */
+    boolean isFunctionalInterface(TypeElement type);
 }

langtools/test/tools/javac/processing/model/util/elements/TestIsFunctionalInterface.java

@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8007574
+ * @summary Test Elements.isFunctionalInterface
+ * @author  Joseph D. Darcy
+ * @library /tools/javac/lib
+ * @build   JavacTestingAbstractProcessor TestIsFunctionalInterface
+ * @compile -processor TestIsFunctionalInterface TestIsFunctionalInterface.java
+ */
+
+import java.util.Set;
+import javax.annotation.processing.*;
+import javax.lang.model.SourceVersion;
+import static javax.lang.model.SourceVersion.*;
+import javax.lang.model.element.*;
+import javax.lang.model.util.*;
+import static javax.lang.model.util.ElementFilter.*;
+import static javax.tools.Diagnostic.Kind.*;
+import static javax.tools.StandardLocation.*;
+import java.io.*;
+
+/**
+ * Test basic workings of Elements.isFunctionalInterface
+ */
+public class TestIsFunctionalInterface extends JavacTestingAbstractProcessor {
+    private int count = 0;
+    public boolean process(Set<? extends TypeElement> annotations,
+                           RoundEnvironment roundEnv) {
+        if (!roundEnv.processingOver()) {
+            for(TypeElement type : typesIn(roundEnv.getElementsAnnotatedWith(ExpectedIsFunInt.class))) {
+                count++;
+                System.out.println(type);
+                if (elements.isFunctionalInterface(type) !=
+                    type.getAnnotation(ExpectedIsFunInt.class).value()) {
+                    messager.printMessage(ERROR,
+                                          "Mismatch between expected and computed isFunctionalInterface",
+                                          type);
+                }
+            }
+        } else {
+            if (count <= 0)
+                messager.printMessage(ERROR, "No types with ExpectedIsFunInt processed.");
+            }
+    return true;
+    }
+}
+
+@interface ExpectedIsFunInt {
+    boolean value();
+}
+
+// Examples below from the lambda specification documents.
+
+@ExpectedIsFunInt(false) // Equals is already an implicit member
+interface Foo1 { boolean equals(Object obj); }
+
+@ExpectedIsFunInt(true) // Bar has one abstract non-Object method
+interface Bar1 extends Foo1 { int compare(String o1, String o2); }
+
+
+@ExpectedIsFunInt(true) // Comparator has one abstract non-Object method
+interface LocalComparator<T> {
+ boolean equals(Object obj);
+ int compare(T o1, T o2);
+}
+
+@ExpectedIsFunInt(false) // Method Object.clone is not public
+interface Foo2 {
+  int m();
+  Object clone();
+}
+
+interface X1 { int m(Iterable<String> arg); }
+interface Y1 { int m(Iterable<String> arg); }
+@ExpectedIsFunInt(true) // Two methods, but they have the same signature
+interface Z1 extends X1, Y1 {}
+
+interface X2 { Iterable m(Iterable<String> arg); }
+interface Y2 { Iterable<String> m(Iterable arg); }
+@ExpectedIsFunInt(true) // Y.m is a subsignature & return-type-substitutable
+interface Z2 extends X2, Y2 {}
+
+interface Action<T> {
+    T doit();
+}
+@ExpectedIsFunInt(true)
+interface LocalExecutor { <T> T execute(Action<T> a); }
+
+interface X5 { <T> T execute(Action<T> a); }
+interface Y5 { <S> S execute(Action<S> a); }
+@ExpectedIsFunInt(true) // Functional: signatures are "the same"
+interface Exec5 extends X5, Y5 {}