Method findSAM

src/main/java/org/codehaus/groovy/ast/ClassHelper.java:647–678

Returns the single abstract method of a class node, if it is a SAM type, or null otherwise. @param type a type for which to search for a single abstract method @return the method node if type is a SAM type, null otherwise

(final ClassNode type)

     * @return the method node if type is a SAM type, null otherwise
     */
    public static MethodNode findSAM(final ClassNode type) {
        if (type == null) return null;
        if (type.isInterface()) {
            MethodNode sam = null;
            for (MethodNode mn : type.getAbstractMethods()) {
                // ignore methods that will have an implementation
                if (Traits.hasDefaultImplementation(mn)) continue;

                final String name = mn.getName();
                if (OBJECT_METHOD_NAME_SET.contains(name)) {
                    // Avoid unnecessary checking for `Object` methods as possible as we could
                    if (OBJECT_TYPE.getDeclaredMethod(name, mn.getParameters()) != null) continue;
                }

                // we have two methods, so no SAM
                if (sam != null) return null;
                sam = mn;
            }
            return sam;
        }
        if (type.isAbstract()) {
            MethodNode sam = null;
            for (MethodNode mn : type.getAbstractMethods()) {
                if (!hasUsableImplementation(type, mn)) {
                    if (sam != null) return null;
                    sam = mn;
                }
            }
            return sam;
        }
        return null;
    }

    private static boolean hasUsableImplementation(final ClassNode c, final MethodNode m) {
        ClassNode declaringClass = m.getDeclaringClass();