Module openj9.dtfj

Package com.ibm.dtfj.java

Interface JavaClass

All Known Implementing Classes:

DTFJJavaClass, JavaAbstractClass, JavaArrayClass, JavaClass, JCJavaClass

public interface JavaClass

Represents a Java class.

Field Summary

Fields

Modifier and Type	Field	Description
static final int	MODIFIERS_UNAVAILABLE	MODIFIERS_UNAVAILABLE is returned by getModifiers() when the modifiers are unavailable.

Method Summary

Modifier and Type	Method	Description
boolean	equals(Object obj)	Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.
JavaClassLoader	getClassLoader()	Fetch the class loader associated with this class.
JavaClass	getComponentType()	For array classes, returns a JavaClass representing the component type of this array class.
Iterator	getConstantPoolReferences()	Java classes may refer to other classes and to String objects via the class's constant pool.
Iterator	getDeclaredFields()	Get the set of fields declared in this class.
Iterator	getDeclaredMethods()	Get the set of methods declared in this class.
ImagePointer	getID()	The ID of a class is a pointer to a section of memory which identifies the class.
long	getInstanceSize()	Returns the size in bytes of an instance of this class on the heap.
Iterator	getInterfaces()	Get the set of names of interfaces directly implemented by this class.
int	getModifiers()	Return the Java language modifiers for this class.
String	getName()	Get the name of the class.
JavaObject	getObject()	Fetch the java.lang.Class object associated with this class.
JavaObject	getProtectionDomain()	Returns the protection domain for this class.
Iterator	getReferences()	Get the set of references from this class.
JavaClass	getSuperclass()	Get the immediate superclass of this class.
int	hashCode()	Answers an integer hash code for the receiver.
boolean	isArray()	Is this an array class ?

Field Details

MODIFIERS_UNAVAILABLE

static final int MODIFIERS_UNAVAILABLE

MODIFIERS_UNAVAILABLE is returned by getModifiers() when the modifiers are unavailable. The value 0xff000000 is chosen as it is a value that can never return true to any of the java.reflect.Modifier methods that test the modifier: isNative(), isPublic(), etc. while at the same time not being 0 which is a possible value when no modifier at all is present i.e. "default". All other values for the modifier returned are defined in java.lang.reflect.Modifiers

See Also:

• Modifier
• Constant Field Values

Method Details

getObject

JavaObject getObject()
              throws CorruptDataException

Fetch the java.lang.Class object associated with this class.

In some implementations this may be null if no object has been created to represent this class, or if the class is synthetic.

Returns:

the java.lang.Class object associated with this class

Throws:

CorruptDataException

See Also:

• getID()

getClassLoader

JavaClassLoader getClassLoader()
                        throws CorruptDataException

Fetch the class loader associated with this class. Classes defined in the bootstrap class loader (including classes representing primitive types or void) will always return a JavaClassLoader representing the bootstrap class loader. This asymmetry with java.lang.Class#getClassLoader() is intentional.

Returns:

the JavaClassLoader in which this class was defined

Throws:

CorruptDataException - if the class loader for this class cannot be found (a class cannot exist without a loader so this implies corruption)

getName

String getName()
        throws CorruptDataException

Get the name of the class.

Returns:

the name of the class in the form: "full/package/class$innerclass"

Throws:

CorruptDataException

getSuperclass

JavaClass getSuperclass()
                 throws CorruptDataException

Get the immediate superclass of this class.

Returns:

the immediate superclass of this class, or null if this class has no superclass. For interfaces, Object, primitive types and void null is always returned.

Throws:

CorruptDataException

getInterfaces

Iterator getInterfaces()

Get the set of names of interfaces directly implemented by this class.

Returns:

an iterator over the collection of the names of interfaces directly implemented by this class. Some JVM implementations may choose to load interfaces lazily, so only the names are returned. The JavaClass objects may be found through the defining class loader.

See Also:

• String
• JavaClassLoader.findClass(String)
• CorruptData

getModifiers

int getModifiers()
          throws CorruptDataException

Return the Java language modifiers for this class.

The modifiers are defined by the JVM Specification.

Return MODIFIERS_UNAVAILABLE if the modifiers are unavailable. This might be the case if DTFJ is operating against an artefact such as a portable heap dump that does not contain information about a class's modifiers.

Note that, for inner classes, the actual modifiers are returned, not the synthetic modifiers. For instance, a class will never have its 'protected' modifier set, even if the inner class was a protected member, since 'protected' is not a legal modifier for a class file.

Returns:

the modifiers for this class

Throws:

CorruptDataException

isArray

boolean isArray()
         throws CorruptDataException

Is this an array class ?

Returns:

true if this class is an array class

Throws:

CorruptDataException

getComponentType

JavaClass getComponentType()
                    throws CorruptDataException

For array classes, returns a JavaClass representing the component type of this array class.

Returns:

a JavaClass representing the component type of this array class

Throws:

CorruptDataException

IllegalArgumentException - if this JavaClass does not represent an array class

getDeclaredFields

Iterator getDeclaredFields()

Get the set of fields declared in this class.

Returns:

an iterator over the collection of fields declared in this class.

See Also:

• JavaField
• CorruptData

getDeclaredMethods

Iterator getDeclaredMethods()

Get the set of methods declared in this class.

Returns:

an iterator over the collection of methods declared in this class.

See Also:

• JavaMethod
• CorruptData

getConstantPoolReferences

Iterator getConstantPoolReferences()

Java classes may refer to other classes and to String objects via the class's constant pool. These references are followed by the garbage collector, forming edges on the graph of reachable objects. This getConstantPoolReferences() may be used to determine which objects are referred to by the receiver's constant pool.

Although Java VMs typically permit only Class and String objects in the constant pool, some esoteric or future virtual machines may permit other types of objects to occur in the constant pool. This API imposes no restrictions on the types of JavaObjects which might be included in the Iterator.

No assumption should be made about the order in which constant pool references are returned.

Classes may also refer to objects through static variables. These may be found with the getDeclaredFields() API. Objects referenced by static variables are not returned by getConstantPoolReferences() unless the object is also referenced by the constant pool.

Returns:

an iterator over the collection of JavaObjects which are referred to by the constant pool of this class

See Also:

• JavaObject
• CorruptData

getID

ImagePointer getID()

The ID of a class is a pointer to a section of memory which identifies the class. The contents of this memory are implementation defined.

In some implementations getID() and getObject().getID() may return the same value. This implies that the class object is also the primary internal representation of the class. DTFJ users should not rely on this behaviour.

In some implementations, getID() may return null for some classes. This indicates that the class is a synthetic class which has been constructed for DTFJ purposes only. The class has no physical representation in the VM.

Returns:

a pointer to the class

getReferences

Iterator getReferences()

Get the set of references from this class.

Returns:

an iterator of JavaReferences

See Also:

• JavaReference
• CorruptData

equals

boolean equals(Object obj)

Description copied from class: java.lang.Object

Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison. The implementation in Object answers true only if the argument is the exact same object as the receiver (==).

Overrides:

equals in class Object

Parameters:

obj -

Returns:

True if the given object refers to the same Java Class in the image

See Also:

• Object.hashCode()

getInstanceSize

long getInstanceSize()
              throws DataUnavailable,
CorruptDataException

Returns the size in bytes of an instance of this class on the heap.

The call is only meaningful for a non-array JavaClass, where all instances of the class are of the same size. If this method is called on a JavaArrayClass, where instances can be of different sizes, an UnsupportedOperationException will be thrown. DataUnavailable can be thrown if no value is available: for example when DTFJ is examining a javacore, where the instance size for a class is not recorded.

Returns:

size in bytes of an instance

Throws:

DataUnavailable

CorruptDataException

UnsupportedOperationException - if the JavaClass is an instance of JavaArrayClass

Since:

1.6

hashCode

int hashCode()

Description copied from class: java.lang.Object

Answers an integer hash code for the receiver. Any two objects which answer true when passed to .equals must answer the same value for this method.

Overrides:

hashCode in class Object

Returns:

the receiver's hash.

See Also:

• Object.equals(java.lang.Object)

getProtectionDomain

JavaObject getProtectionDomain()
                        throws DataUnavailable,
CorruptDataException

Returns the protection domain for this class.

Returns:

the protection domain or null for the default protection domain

Throws:

DataUnavailable

CorruptDataException

Since:

9