https://openjdk.java.net/ 
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package jdk.vm.ci.meta;

import java.lang.invoke.MethodHandle;


Reflection operations on values represented as constants. All methods in this interface require the VM to access the actual object encapsulated in object constants. This access is not always possible, depending on kind of VM and the state that the VM is in. Therefore, all methods can return null at any time, to indicate that the result is not available at this point. The caller is responsible to check for null results and handle them properly, e.g., not perform an optimization. 
/**
 * Reflection operations on values represented as {@linkplain JavaConstant constants}. All methods
 * in this interface require the VM to access the actual object encapsulated in
 * {@link JavaKind#Object object} constants. This access is not always possible, depending on kind
 * of VM and the state that the VM is in. Therefore, all methods can return {@code null} at any
 * time, to indicate that the result is not available at this point. The caller is responsible to
 * check for {@code null} results and handle them properly, e.g., not perform an optimization.
 */
public interface ConstantReflectionProvider {

    
Compares two constants for equality. The equality relationship is symmetric. Returns true if the two constants represent the same run time value, false if they are different. Returns null if the constants cannot be compared at this point. 
/**
     * Compares two constants for equality. The equality relationship is symmetric. Returns
     * {@link Boolean#TRUE true} if the two constants represent the same run time value,
     * {@link Boolean#FALSE false} if they are different. Returns {@code null} if the constants
     * cannot be compared at this point.
     */
    Boolean constantEquals(Constant x, Constant y);

    
Returns the length of the array constant. Returns null if the constant is not an array, or if the array length is not available at this point. 
/**
     * Returns the length of the array constant. Returns {@code null} if the constant is not an
     * array, or if the array length is not available at this point.
     */
    Integer readArrayLength(JavaConstant array);

    
Reads a value from the given array at the given index. Returns null if the constant is not an array, if the index is out of bounds, or if the value is not available at this point. 
/**
     * Reads a value from the given array at the given index. Returns {@code null} if the constant
     * is not an array, if the index is out of bounds, or if the value is not available at this
     * point.
     */
    JavaConstant readArrayElement(JavaConstant array, int index);

    
Gets the current value of this field for a given object, if available.
There is no guarantee that the same value will be returned by this method for a field unless
the field is considered to be constant by the runtime.

Params:
  • receiver – object from which this field's value is to be read. This value is ignored if
           this field is static.
Returns:the value of this field or null if the value is not available (e.g., because the field holder is not yet initialized).
/**
     * Gets the current value of this field for a given object, if available.
     *
     * There is no guarantee that the same value will be returned by this method for a field unless
     * the field is considered to be constant by the runtime.
     *
     * @param receiver object from which this field's value is to be read. This value is ignored if
     *            this field is static.
     * @return the value of this field or {@code null} if the value is not available (e.g., because
     *         the field holder is not yet initialized).
     */
    JavaConstant readFieldValue(ResolvedJavaField field, JavaConstant receiver);

    
Converts the given primitive constant to a boxed object constant, according to the Java boxing rules. Returns null if the source is is not a primitive constant, or the boxed value is not available at this point. 
/**
     * Converts the given {@link JavaKind#isPrimitive() primitive} constant to a boxed
     * {@link JavaKind#Object object} constant, according to the Java boxing rules. Returns
     * {@code null} if the source is is not a primitive constant, or the boxed value is not
     * available at this point.
     */
    JavaConstant boxPrimitive(JavaConstant source);

    
Converts the given object constant to a 
primitive constant, according to the Java unboxing rules. Returns null if the source is is not an object constant that can be unboxed, or the unboxed value is not available at this point. 
/**
     * Converts the given {@link JavaKind#Object object} constant to a {@link JavaKind#isPrimitive()
     * primitive} constant, according to the Java unboxing rules. Returns {@code null} if the source
     * is is not an object constant that can be unboxed, or the unboxed value is not available at
     * this point.
     */
    JavaConstant unboxPrimitive(JavaConstant source);

    
Gets a string as a JavaConstant. 
/**
     * Gets a string as a {@link JavaConstant}.
     */
    JavaConstant forString(String value);

    
Returns the ResolvedJavaType for a Class object (or any other object regarded as a class by the VM) encapsulated in the given constant. Returns null if the constant does not encapsulate a class, or if the type is not available at this point. 
/**
     * Returns the {@link ResolvedJavaType} for a {@link Class} object (or any other object regarded
     * as a class by the VM) encapsulated in the given constant. Returns {@code null} if the
     * constant does not encapsulate a class, or if the type is not available at this point.
     */
    ResolvedJavaType asJavaType(Constant constant);

    
Gets access to the internals of MethodHandle. 
/**
     * Gets access to the internals of {@link MethodHandle}.
     */
    MethodHandleAccessProvider getMethodHandleAccess();

    
Gets raw memory access.

/**
     * Gets raw memory access.
     */
    MemoryAccessProvider getMemoryAccessProvider();

    
Gets the runtime representation of the Class object of this type. 
/**
     * Gets the runtime representation of the {@link Class} object of this type.
     */
    JavaConstant asJavaClass(ResolvedJavaType type);

    
Gets the runtime representation of the "hub" of this type--that is, the closest part of the
type representation which is typically stored in the object header.

/**
     * Gets the runtime representation of the "hub" of this type--that is, the closest part of the
     * type representation which is typically stored in the object header.
     */
    Constant asObjectHub(ResolvedJavaType type);
}