Class Guards
java.lang.Object
jdk.dynalink.linker.support.Guards
Utility methods for creating typical guards for
 
MethodHandles.guardWithTest(MethodHandle, MethodHandle, MethodHandle)
 and for adjusting their method types.- Since:
- 9
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Method SummaryModifier and TypeMethodDescriptionstatic MethodHandleasType(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 MethodHandleasType(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 MethodHandlegetClassGuard(Class<?> clazz) Creates a guard method that tests its only argument for being of an exact particular class.static MethodHandlegetIdentityGuard(Object obj) Creates a guard method that tests its only argument for being referentially identical to another objectstatic MethodHandlegetInstanceOfGuard(Class<?> clazz) Creates a guard method that tests its only argument for being an instance of a particular class.static MethodHandleisArray(int pos, MethodType type) Creates a method handle that returns true if the argument in the specified position is a Java array.static MethodHandleisInstance(Class<?> clazz, int pos, MethodType type) Creates a method handle with arguments of a specified type, but with boolean return value.static MethodHandleisInstance(Class<?> clazz, MethodType type) Creates a method handle with arguments of a specified type, but with boolean return value.static MethodHandleReturns a guard that tests whether the first argument is not null.static MethodHandleisNull()Returns a guard that tests whether the first argument is null.static MethodHandleisOfClass(Class<?> clazz, MethodType type) Creates a guard method handle with arguments of a specified type, but with boolean return value.
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Method Details- 
isOfClassCreates 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.
 
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isInstanceCreates 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.
 
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isInstanceCreates 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.
 
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isArrayCreates 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.
 
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asTypeTakes a method handle intended to be used as a guard, and adapts it to the requested type, but returning a boolean. AppliesMethodHandle.asType(MethodType)to convert types and usesMethodHandles.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
 
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asTypepublic 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. AppliesLinkerServices.asType(MethodHandle, MethodType)to convert types and usesMethodHandles.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
 
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getClassGuardCreates 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.
 
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getInstanceOfGuardCreates 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.
 
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getIdentityGuardCreates 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.
 
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isNullReturns a guard that tests whether the first argument is null.- Returns:
- a guard that tests whether the first argument is null.
 
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isNotNullReturns a guard that tests whether the first argument is not null.- Returns:
- a guard that tests whether the first argument is not null.
 
 
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