1 /*
   2  * Copyright (c) 2012, 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 package jdk.vm.ci.meta;
  24 
  25 import java.lang.invoke.MethodHandle;
  26 
  27 /**
  28  * Reflection operations on values represented as {@linkplain JavaConstant constants}. All methods
  29  * in this interface require the VM to access the actual object encapsulated in
  30  * {@link JavaKind#Object object} constants. This access is not always possible, depending on kind
  31  * of VM and the state that the VM is in. Therefore, all methods can return {@code null} at any
  32  * time, to indicate that the result is not available at this point. The caller is responsible to
  33  * check for {@code null} results and handle them properly, e.g., not perform an optimization.
  34  */
  35 public interface ConstantReflectionProvider {
  36 
  37     /**
  38      * Compares two constants for equality. The equality relationship is symmetric. Returns
  39      * {@link Boolean#TRUE true} if the two constants represent the same run time value,
  40      * {@link Boolean#FALSE false} if they are different. Returns {@code null} if the constants
  41      * cannot be compared at this point.
  42      */
  43     Boolean constantEquals(Constant x, Constant y);
  44 
  45     /**
  46      * Returns the length of the array constant. Returns {@code null} if the constant is not an
  47      * array, or if the array length is not available at this point.
  48      */
  49     Integer readArrayLength(JavaConstant array);
  50 
  51     /**
  52      * Reads a value from the given array at the given index. Returns {@code null} if the constant
  53      * is not an array, if the index is out of bounds, or if the value is not available at this
  54      * point.
  55      */
  56     JavaConstant readArrayElement(JavaConstant array, int index);
  57 
  58     /**
  59      * Gets the current value of this field for a given object, if available.
  60      *
  61      * There is no guarantee that the same value will be returned by this method for a field unless
  62      * the field is considered to be constant by the runtime.
  63      *
  64      * @param receiver object from which this field's value is to be read. This value is ignored if
  65      *            this field is static.
  66      * @return the value of this field or {@code null} if the value is not available (e.g., because
  67      *         the field holder is not yet initialized).
  68      */
  69     JavaConstant readFieldValue(ResolvedJavaField field, JavaConstant receiver);
  70 
  71     /**
  72      * Converts the given {@link JavaKind#isPrimitive() primitive} constant to a boxed
  73      * {@link JavaKind#Object object} constant, according to the Java boxing rules. Returns
  74      * {@code null} if the source is is not a primitive constant, or the boxed value is not
  75      * available at this point.
  76      */
  77     JavaConstant boxPrimitive(JavaConstant source);
  78 
  79     /**
  80      * Converts the given {@link JavaKind#Object object} constant to a {@link JavaKind#isPrimitive()
  81      * primitive} constant, according to the Java unboxing rules. Returns {@code null} if the source
  82      * is is not an object constant that can be unboxed, or the unboxed value is not available at
  83      * this point.
  84      */
  85     JavaConstant unboxPrimitive(JavaConstant source);
  86 
  87     /**
  88      * Gets a string as a {@link JavaConstant}.
  89      */
  90     JavaConstant forString(String value);
  91 
  92     /**
  93      * Returns the {@link ResolvedJavaType} for a {@link Class} object (or any other object regarded
  94      * as a class by the VM) encapsulated in the given constant. Returns {@code null} if the
  95      * constant does not encapsulate a class, or if the type is not available at this point.
  96      */
  97     ResolvedJavaType asJavaType(Constant constant);
  98 
  99     /**
 100      * Gets access to the internals of {@link MethodHandle}.
 101      */
 102     MethodHandleAccessProvider getMethodHandleAccess();
 103 
 104     /**
 105      * Gets raw memory access.
 106      */
 107     MemoryAccessProvider getMemoryAccessProvider();
 108 
 109     /**
 110      * Gets the runtime representation of the {@link Class} object of this type.
 111      */
 112     JavaConstant asJavaClass(ResolvedJavaType type);
 113 
 114     /**
 115      * Gets the runtime representation of the "hub" of this type--that is, the closest part of the
 116      * type representation which is typically stored in the object header.
 117      */
 118     Constant asObjectHub(ResolvedJavaType type);
 119 }