Examples of java.lang.invoke.MethodType

java.lang.invoke.MethodType
A method type represents the arguments and return type accepted and returned by a method handle, or the arguments and return type passed and expected by a method handle caller. Method types must be properly matched between a method handle and all its callers, and the JVM's operations enforce this matching at, specifically during calls to {@link MethodHandle#invokeExact MethodHandle.invokeExact}and {@link MethodHandle#invoke MethodHandle.invoke}, and during execution of {@code invokedynamic} instructions.
The structure is a return type accompanied by any number of parameter types. The types (primitive, {@code void}, and reference) are represented by {@link Class} objects.(For ease of exposition, we treat {@code void} as if it were a type.In fact, it denotes the absence of a return type.)
All instances of {@code MethodType} are immutable.Two instances are completely interchangeable if they compare equal. Equality depends on pairwise correspondence of the return and parameter types and on nothing else.
This type can be created only by factory methods. All factory methods may cache values, though caching is not guaranteed. Some factory methods are static, while others are virtual methods which modify precursor method types, e.g., by changing a selected parameter.
Factory methods which operate on groups of parameter types are systematically presented in two versions, so that both Java arrays and Java lists can be used to work with groups of parameter types. The query methods {@code parameterArray} and {@code parameterList}also provide a choice between arrays and lists.
{@code MethodType} objects are sometimes derived from bytecode instructionssuch as {@code invokedynamic}, specifically from the type descriptor strings associated with the instructions in a class file's constant pool.
Like classes and strings, method types can also be represented directly in a class file's constant pool as constants. A method type may be loaded by an {@code ldc} instruction which refersto a suitable {@code CONSTANT_MethodType} constant pool entry.The entry refers to a {@code CONSTANT_Utf8} spelling for the descriptor string.(For full details on method type constants, see sections 4.4.8 and 5.4.3.5 of the Java Virtual Machine Specification.)
When the JVM materializes a {@code MethodType} from a descriptor string,all classes named in the descriptor must be accessible, and will be loaded. (But the classes need not be initialized, as is the case with a {@code CONSTANT_Class}.) This loading may occur at any time before the {@code MethodType} object is first derived. @author John Rose, JSR 292 EG

        return invokeDynamic("constant_" + binding.getBindingId(), binding.getType(), context.getDefaultBootstrapMethod(), binding.getBindingId());
    }


    public static ByteCodeNode generateInvocation(CompilerContext context, FunctionInfo function, ByteCodeNode getSessionByteCode, List<ByteCodeNode> arguments, Binding binding)
    {
        MethodType methodType = binding.getType();


        Signature signature = function.getSignature();
        Class<?> unboxedReturnType = Primitives.unwrap(methodType.returnType());


        LabelNode end = new LabelNode("end");
        Block block = new Block(context)
                .setDescription("invoke " + signature);


        ArrayList<Class<?>> stackTypes = new ArrayList<>();


        int index = 0;
        for (Class<?> type : methodType.parameterArray()) {
            stackTypes.add(type);
            if (type == ConnectorSession.class) {
                block.append(getSessionByteCode);
            }
            else {
                block.append(arguments.get(index));
                index++;
                block.append(ByteCodeUtils.ifWasNullPopAndGoto(context, end, unboxedReturnType, Lists.reverse(stackTypes)));
            }
        }
        block.append(invoke(context, binding));


        if (function.isNullable()) {
            if (unboxedReturnType.isPrimitive()) {
                LabelNode notNull = new LabelNode("notNull");
                block.dup(methodType.returnType())
                        .ifNotNullGoto(notNull)
                        .putVariable("wasNull", true)
                        .comment("swap boxed null with unboxed default")
                        .pop(methodType.returnType())
                        .pushJavaDefault(unboxedReturnType)
                        .gotoLabel(end)
                        .visitLabel(notNull)
                        .append(ByteCodeUtils.unboxPrimitive(context, unboxedReturnType));
            }
            else {
                block.dup(methodType.returnType())
                        .ifNotNullGoto(end)
                        .putVariable("wasNull", true);
            }
        }
        block.visitLabel(end);

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    private static MethodHandle fixMethodHandleType(Field field, MethodHandle mh) throws IllegalAccessException {
        if (mh == null)
            return null;


        final MethodType origType = mh.type();
        final Class<?>[] params = origType.parameterArray();


        params[0] = Object.class;
        for (int i = 1; i < params.length; i++) {
            if (!params[i].isPrimitive())
                params[i] = Object.class;
        }


        Class<?> rtype = origType.returnType();
        if (field instanceof Field.ArrayField && rtype.isArray()) {
            if (!rtype.getComponentType().isPrimitive())
                rtype = Object[].class;
        } else if (!rtype.isPrimitive())
            rtype = Object.class;


        final MethodType mt = MethodType.methodType(rtype, params);
        return mh.asType(mt);
    }

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    }


    try {
      Class<?>[] parameterTypes = method.getParameterTypes();


      MethodType description = MethodType.methodType(method.getReturnType(), parameterTypes);


      Lookup lookup = MethodHandles.lookup();


      MethodHandle originalHandle = lookup.findVirtual(type, method.getName(), description);

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                binding.getType().returnType());
    }


    public static ByteCodeNode generateInvocation(CompilerContext context, FunctionInfo function, List<ByteCodeNode> arguments, Binding binding)
    {
        MethodType methodType = binding.getType();


        Signature signature = function.getSignature();
        Class<?> unboxedReturnType = Primitives.unwrap(methodType.returnType());


        LabelNode end = new LabelNode("end");
        Block block = new Block(context)
                .setDescription("invoke " + signature);


        List<Class<?>> stackTypes = new ArrayList<>();


        int index = 0;
        for (Class<?> type : methodType.parameterArray()) {
            stackTypes.add(type);
            if (type == ConnectorSession.class) {
                block.getVariable("session");
            }
            else {
                block.append(arguments.get(index));
                if (!function.getNullableArguments().get(index)) {
                    block.append(ifWasNullPopAndGoto(context, end, unboxedReturnType, Lists.reverse(stackTypes)));
                }
                else {
                    block.append(boxPrimitiveIfNecessary(context, type));
                    block.putVariable("wasNull", false);
                }
                index++;
            }
        }
        block.append(invoke(context, binding, function.getSignature()));


        if (function.isNullable()) {
            if (unboxedReturnType.isPrimitive()) {
                LabelNode notNull = new LabelNode("notNull");
                block.dup(methodType.returnType())
                        .ifNotNullGoto(notNull)
                        .putVariable("wasNull", true)
                        .comment("swap boxed null with unboxed default")
                        .pop(methodType.returnType())
                        .pushJavaDefault(unboxedReturnType)
                        .gotoLabel(end)
                        .visitLabel(notNull)
                        .append(unboxPrimitive(context, unboxedReturnType));
            }
            else {
                block.dup(methodType.returnType())
                        .ifNotNullGoto(end)
                        .putVariable("wasNull", true);
            }
        }
        block.visitLabel(end);

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     * Apply a transformer as filter.
     * The filter may not match exactly in the types. In this case needed
     * additional type transformations are done by {@link MethodHandle#asType(MethodType)} 
     */
    public static MethodHandle applyUnsharpFilter(MethodHandle handle, int pos, MethodHandle transformer) {
        MethodType type = transformer.type();
        Class given = handle.type().parameterType(pos);
        if (type.returnType() != given || type.parameterType(0) != given) {
            transformer = transformer.asType(MethodType.methodType(given, type.parameterType(0)));
        }
        return MethodHandles.filterArguments(handle, pos, transformer);
    }

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                // and the meta class.


                // to do this we first bind the values to #setBeanProperties
                MethodHandle con = BEAN_CONSTRUCTOR_PROPERTY_SETTER.bindTo(mc);
                // inner class case
                MethodType foldTargetType = MethodType.methodType(Object.class);
                if (args.length==3) {
                    con = MethodHandles.dropArguments(con, 1, targetType.parameterType(1));
                    foldTargetType = foldTargetType.insertParameterTypes(0, targetType.parameterType(1));
                }
                handle = MethodHandles.foldArguments(con, handle.asType(foldTargetType));
            }
            if (method instanceof MetaConstructor) {
                handle = MethodHandles.dropArguments(handle, 0, Class.class);

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            Class[] pt = handle.type().parameterArray();
            if (currentType!=null) pt = currentType.parameterArray();
            for (int i=1; i<args.length; i++) {
                if (args[i] instanceof Wrapper) {
                    Class type = pt[i];
                    MethodType mt = MethodType.methodType(type, Wrapper.class);
                    handle = MethodHandles.filterArguments(handle, i, UNWRAP_METHOD.asType(mt));
                    if (LOG_ENABLED) LOG.info("added filter for Wrapper for argument at pos "+i);
                }
            }
        }

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            //TODO: if we would know exactly which paths require the exceptions
            //      and which paths not, we can sometimes save this guard 
            if (handle==null || catchException==false) return;
            Class returnType = handle.type().returnType();
            if (returnType!=Object.class) {
                MethodType mtype = MethodType.methodType(returnType, GroovyRuntimeException.class); 
                handle = MethodHandles.catchException(handle, GroovyRuntimeException.class, UNWRAP_EXCEPTION.asType(mtype));
            } else {
                handle = MethodHandles.catchException(handle, GroovyRuntimeException.class, UNWRAP_EXCEPTION);
            }
            if (LOG_ENABLED) LOG.info("added GroovyRuntimeException unwrapper");

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    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws Throwable {
        for (int i = 0; i < 25600; i++) {
            MethodType mt = MethodType.methodType(java.lang.String.class);
            System.out.println(mt);
            MethodType mt3 = null;
            try {
              mt3 = MethodType.genericMethodType(i);
            } catch (IllegalArgumentException e) {
              System.out.println("Passed");
              System.exit(95);

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public class SpreadNullArg {


  public static void main(String args[]) {


    MethodType mt_ref_arg = MethodType.methodType(int.class, Integer.class);
    MethodHandle mh_spreadInvoker = MethodHandles.spreadInvoker(mt_ref_arg, 0);
    MethodHandle mh_spread_target;
    int result = 42;


    try {

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