Module jdk.dynalink

Package jdk.dynalink.linker.support

Class Guards

java.lang.Object

jdk.dynalink.linker.support.Guards

public final class Guards
extends Object

Utility methods for creating typical guards for MethodHandles.guardWithTest(MethodHandle, MethodHandle, MethodHandle) and for adjusting their method types.

Method Summary

Modifier and Type	Method	Description
static MethodHandle	asType(MethodHandle test, MethodType type)	Takes a method handle intended to be used as a guard, and adapts it to the requested type, but returning a boolean.
static MethodHandle	asType(LinkerServices linkerServices, MethodHandle test, MethodType type)	Takes a method handle intended to be used as a guard, and adapts it to the requested type, but returning a boolean.
static MethodHandle	getClassGuard(Class<?> clazz)	Creates a guard method that tests its only argument for being of an exact particular class.
static MethodHandle	getIdentityGuard(Object obj)	Creates a guard method that tests its only argument for being referentially identical to another object
static MethodHandle	getInstanceOfGuard(Class<?> clazz)	Creates a guard method that tests its only argument for being an instance of a particular class.
static MethodHandle	isArray(int pos, MethodType type)	Creates a method handle that returns true if the argument in the specified position is a Java array.
static MethodHandle	isInstance(Class<?> clazz, int pos, MethodType type)	Creates a method handle with arguments of a specified type, but with boolean return value.
static MethodHandle	isInstance(Class<?> clazz, MethodType type)	Creates a method handle with arguments of a specified type, but with boolean return value.
static MethodHandle	isNotNull()	Returns a guard that tests whether the first argument is not null.
static MethodHandle	isNull()	Returns a guard that tests whether the first argument is null.
static MethodHandle	isOfClass(Class<?> clazz, MethodType type)	Creates a guard method handle with arguments of a specified type, but with boolean return value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

isOfClass

public static MethodHandle isOfClass(Class<?> clazz,
                                     MethodType type)

Creates a guard method handle with arguments of a specified type, but with boolean return value. When invoked, it returns true if the first argument is of the specified class (exactly of it, not a subclass). The rest of the arguments will be ignored.

Parameters:

clazz - the class of the first argument to test for

type - the method type

Returns:

a method handle testing whether its first argument is of the specified class.

isInstance

public static MethodHandle isInstance(Class<?> clazz,
                                      MethodType type)

Creates a method handle with arguments of a specified type, but with boolean return value. When invoked, it returns true if the first argument is instance of the specified class or its subclass). The rest of the arguments will be ignored.

Parameters:

clazz - the class of the first argument to test for

type - the method type

Returns:

a method handle testing whether its first argument is of the specified class or subclass.

isInstance

public static MethodHandle isInstance(Class<?> clazz,
                                      int pos,
                                      MethodType type)

Creates a method handle with arguments of a specified type, but with boolean return value. When invoked, it returns true if the n'th argument is instance of the specified class or its subclass). The rest of the arguments will be ignored.

Parameters:

clazz - the class of the first argument to test for

pos - the position on the argument list to test

type - the method type

Returns:

a method handle testing whether its first argument is of the specified class or subclass.

isArray

public static MethodHandle isArray(int pos,
                                   MethodType type)

Creates a method handle that returns true if the argument in the specified position is a Java array.

Parameters:

pos - the position in the argument lit

type - the method type of the handle

Returns:

a method handle that returns true if the argument in the specified position is a Java array; the rest of the arguments are ignored.

asType

public static MethodHandle asType(MethodHandle test,
                                  MethodType type)

Takes a method handle intended to be used as a guard, and adapts it to the requested type, but returning a boolean. Applies MethodHandle.asType(MethodType) to convert types and uses MethodHandles.dropArguments(MethodHandle, int, Class...) to match the requested type arity.

Parameters:

test - the test method handle

type - the type to adapt the method handle to

Returns:

the adapted method handle

asType

public static MethodHandle asType(LinkerServices linkerServices,
                                  MethodHandle test,
                                  MethodType type)

Takes a method handle intended to be used as a guard, and adapts it to the requested type, but returning a boolean. Applies LinkerServices.asType(MethodHandle, MethodType) to convert types and uses MethodHandles.dropArguments(MethodHandle, int, Class...) to match the requested type arity.

Parameters:

linkerServices - the linker services to use for type conversions

test - the test method handle

type - the type to adapt the method handle to

Returns:

the adapted method handle

getClassGuard

public static MethodHandle getClassGuard(Class<?> clazz)

Creates a guard method that tests its only argument for being of an exact particular class.

Parameters:

clazz - the class to test for.

Returns:

the desired guard method.

getInstanceOfGuard

public static MethodHandle getInstanceOfGuard(Class<?> clazz)

Creates a guard method that tests its only argument for being an instance of a particular class.

Parameters:

clazz - the class to test for.

Returns:

the desired guard method.

getIdentityGuard

public static MethodHandle getIdentityGuard(Object obj)

Creates a guard method that tests its only argument for being referentially identical to another object

Parameters:

obj - the object used as referential identity test

Returns:

the desired guard method.

isNull

public static MethodHandle isNull()

Returns a guard that tests whether the first argument is null.

Returns:

a guard that tests whether the first argument is null.

isNotNull

public static MethodHandle isNotNull()

Returns a guard that tests whether the first argument is not null.

Returns:

a guard that tests whether the first argument is not null.