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.
Since:
9

  • 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 declared in class Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    Modifier and Type
    Method
    Description
    protected Object
    clone()
    Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
    boolean
    equals(Object o)
    Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.
    protected void
    finalize()
    Deprecated, for removal: This API element is subject to removal in a future version.
    May cause performance issues, deadlocks and hangs.
    final Class<? extends Object>
    getClass()
    Answers the unique instance of java.lang.Class which represents the class of the receiver.
    int
    hashCode()
    Answers an integer hash code for the receiver.
    final void
    notify()
    Causes one thread which is waiting on the receiver to be made ready to run.
    final void
    notifyAll()
    Causes all threads which are waiting on the receiver to be made ready to run.
    String
    toString()
    Answers a string containing a concise, human-readable description of the receiver.
    final void
    wait()
    Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).
    final void
    wait(long time)
    Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.
    final void
    wait(long time, int frac)
    Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

  • Method Details

    • 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.