The set of base values (IsReferenceValue) this value abstracts over. This set is never empty and contains this value if this value does not (further) abstract over other reference values; otherwise it only contains the base values, but not this value.

Returns the type of the upper type bound if the upper type bound contains exactly one element. That is, the function is only always defined iff the type is precise.

In general an IsReferenceValue abstracts over all potential values and this information is sufficient for subsequent analyses; but in some cases, analyzing the set of underlying values may increase the overall precision and this set is returned by this function. In other words: if baseValues is nonEmpty, then the properties returned by this value are derived from the base values, but still maybe more specific. For example,

Object o = _;
if(...) o = f() else o = g();
// when we reach this point, we generally don't know if the values returned by f and g
// are non-null; hence, o is potentially null.
if(o != null)
 // Now, we know that o is not null, but we still don't know if the values returned
 // by f OR g were null and we cannot establish that when we don't know to which value
 // o is actually referring to.
 u(o);

The computational type of the value if this object represents a legal value.

The precise computational type is, e.g., needed to calculate the effect of generic stack manipulation instructions (e.g., DUP_... and SWAP) on the stack as well as to calculate the jump targets of RET instructions and to determine which values are actually copied by, e.g., the dup_XX instructions.

The constant value that this variable takes - if it take a single constant value! I.e., if the variable may take multiple different values at runtime constantValue will return None.

Returns true if and only if the value has the computational type 2; false in all other cases (including the case where this value is illegal!).

Returns Yes if the value is _not null_ and the least upper type bound is an ArrayType; the value is Unknown if the least upper type bound is ArrayType but the value may be null; in all other cases No is returned; in particular if the value is known to be null. No is also returned if the value's type is Object or Seriablizable or Cloneable.

Returns true iff this value is not a legal value according to the JVM specification. Such values cannot be used to perform any computations and will generally not occur in static analyses unless the analysis or the bytecode is buggy.

If Yes the value is known to always be null at runtime. In this case the upper bound is (has to be) empty. If the answer is Unknown then the analysis was not able to statically determine whether the value is null or is not null. In this case the upper bound is expected to be non-empty. If the answer is No then the value is statically known not to be null. In this case, the upper bound may precisely identify the runtime type or still just identify an upper bound.

Returns true if the type information is precise. I.e., the type returned by upperTypeBound precisely models the runtime type of the value. If, isPrecise returns true, the type of this value can generally be assumed to represent a class type (not an interface type) or an array type. However, this domain also supports the case that isPrecise returns true even though the associated type identifies an interface type or an abstract class type. The later case may be interesting in the context of classes that are generated at run time.

Returns true in case of a value with primitive type.

Returns true if the value has a reference type.

Tests if the type of this value is potentially a subtype of the specified reference type under the assumption that this value is not null. This test takes the precision of the type information into account. That is, if the currently available type information is not precise and the given type has a subtype that is always a subtype of the current upper type bound, then Unknown is returned. Given that it may be computationally intensive to determine whether two types have a common subtype it may be better to just return Unknown in case that this type and the given type are not in a direct inheritance relationship.

Basically, this method implements the same semantics as the ClassHierarchy's isSubtypeOf method, but it additionally checks if the type of this value could be a subtype of the given supertype. I.e., if this value's type identifies a supertype of the given supertype and that type is not known to be precise, the answer is Unknown.

For example, assume that the type of this reference value is java.util.Collection and we know/have to assume that this is only an upper bound. In this case an answer is No if and only if it is impossible that the runtime type is a subtype of the given supertype. This condition holds, for example, for java.io.File which is not a subclass of java.util.Collection and which does not have any further subclasses (in the JDK). I.e., the classes java.io.File and java.util.Collection are not in an inheritance relationship. However, if the specified supertype would be java.util.List the answer would be unknown.

Returns true if this value represents void.

Returns the unique ID that identifies this kind of attribute (Signature, LineNumberTable, ...)

This id can then be used in a switch statement to efficiently identify the attribute.

(attribute.id : @scala.annotation.switch) match {
     case Signature.Id => ...
}

Associating Unique Id

The unique ids are manually associated with the attributes. The attributes use the following IDs:

• (-1 Unknown Attribute)
• 1-5 The ConstantValue Attribute
• 6 The Code Attribute
• 7 The StackMapTable Attribute
• 8 The Exceptions Attribute
• 9 The InnerClasses Attribute
• 10 The EnclosingMethod Attribute
• 11 The Synthetic Attribute
• 12-16 The Signature Attribute
• 17 The SourceFile Attribute
• 18 The SourceDebugExtension Attribute
• 19 The LineNumberTable Attribute
• 20 The LocalVariableTable Attribute
• 21 The LocalVariableTypeTable Attribute
• 22 The Deprecated Attribute
• 23 The RuntimeVisibleAnnotations Attribute
• 24 The RuntimeInvisibleAnnotations Attribute
• 25 The RuntimeVisibleParameterAnnotations Attribute
• 26 The RuntimeInvisibleParameterAnnotations Attribute
• 27 The RuntimeVisibleTypeAnnotations Attribute
• 28 The RuntimeInvisibleTypeAnnotations Attribute
• 29-41 The AnnotationDefault Attribute
• 42 The BootstrapMethods Attribute
• 43 The MethodParameters Attribute
• 44 The Module Attribute (Java 9)
• 45 The ModuleMainClass Attribute (Java 9)
• 46 The ModulePackages Attribute (Java 9)
• 47 The NestHost Attribute (Java 11)
• 48 The NestMembers Attribute (Java 11)
• 49 The Record Attribute (Java 16)
• 1001 OPAL's VirtualTypeFlag Attribute
• 1002 OPAL's SynthesizedClassFiles Attribute
• 1003 OPAL's TACode Attribute (the 3-Address Code)

The least upper type bound of the value.

None if and only if the underlying value is null.

The (runtime) type of the concrete value.

Returns true if this attribute and the given one are guaranteed to be indistinguishable at runtime.

Returns a ValueInformation object that just captures the basic information as defined by this value framework. The returned value information object will be independent of the underlying representation from which it was derived.

The upper bound of the value's type. The upper bound is empty if this value is null (i.e., isNull == Yes). The upper bound is only guaranteed to contain exactly one type if the type is precise. (i.e., isPrecise == true). Otherwise, the upper type bound may contain one or more types that are not known to be in an inheritance relation, but which will correctly approximate the runtime type.

The concrete value.

A string representation of the concrete value; used for debugging purposes.

The type of this value as used by the org.opalj.br.StackMapTable attribute.