org.datanucleus.enhancer.asm

Class Attribute

java.lang.Object

org.datanucleus.enhancer.asm.Attribute

public class Attribute
extends Object

A non standard class, field, method or code attribute, as defined in the Java Virtual Machine Specification (JVMS).

Author:

Eric Bruneton, Eugene Kuleshov

See Also:

JVMS 4.7, JVMS 4.7.3

Field Summary

Fields

Modifier and Type	Field and Description
String	type The type of this attribute, also called its name in the JVMS.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Attribute(String type) Constructs a new empty attribute.

Method Summary

Modifier and Type	Method and Description
protected Label[]	getLabels() Returns the labels corresponding to this attribute.
boolean	isCodeAttribute() Returns true if this type of attribute is a code attribute.
boolean	isUnknown() Returns true if this type of attribute is unknown.
protected Attribute	read(ClassReader classReader, int offset, int length, char[] charBuffer, int codeAttributeOffset, Label[] labels) Reads a type attribute.
protected ByteVector	write(ClassWriter classWriter, byte[] code, int codeLength, int maxStack, int maxLocals) Returns the byte array form of the content of this attribute.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

type

public final String type

The type of this attribute, also called its name in the JVMS.

Constructor Detail

Attribute

protected Attribute(String type)

Constructs a new empty attribute.

Parameters:

type - the type of the attribute.

Method Detail

isUnknown

public boolean isUnknown()

Returns true if this type of attribute is unknown. This means that the attribute content can't be parsed to extract constant pool references, labels, etc. Instead, the attribute content is read as an opaque byte array, and written back as is. This can lead to invalid attributes, if the content actually contains constant pool references, labels, or other symbolic references that need to be updated when there are changes to the constant pool, the method bytecode, etc. The default implementation of this method always returns true.

Returns:

true if this type of attribute is unknown.

isCodeAttribute

public boolean isCodeAttribute()

Returns true if this type of attribute is a code attribute.

Returns:

true if this type of attribute is a code attribute.

getLabels

protected Label[] getLabels()

Returns the labels corresponding to this attribute.

Returns:

the labels corresponding to this attribute, or null if this attribute is not a code attribute that contains labels.

read

protected Attribute read(ClassReader classReader,
                         int offset,
                         int length,
                         char[] charBuffer,
                         int codeAttributeOffset,
                         Label[] labels)

Reads a type attribute. This method must return a new Attribute object, of type type, corresponding to the 'length' bytes starting at 'offset', in the given ClassReader.

Parameters:

classReader - the class that contains the attribute to be read.

offset - index of the first byte of the attribute's content in ClassReader.b. The 6 attribute header bytes (attribute_name_index and attribute_length) are not taken into account here.

length - the length of the attribute's content (excluding the 6 attribute header bytes).

charBuffer - the buffer to be used to call the ClassReader methods requiring a 'charBuffer' parameter.

codeAttributeOffset - index of the first byte of content of the enclosing Code attribute in ClassReader.b, or -1 if the attribute to be read is not a code attribute. The 6 attribute header bytes (attribute_name_index and attribute_length) are not taken into account here.

labels - the labels of the method's code, or null if the attribute to be read is not a code attribute.

Returns:

a new Attribute object corresponding to the specified bytes.

write

protected ByteVector write(ClassWriter classWriter,
                           byte[] code,
                           int codeLength,
                           int maxStack,
                           int maxLocals)

Returns the byte array form of the content of this attribute. The 6 header bytes (attribute_name_index and attribute_length) must not be added in the returned ByteVector.

Parameters:

classWriter - the class to which this attribute must be added. This parameter can be used to add the items that corresponds to this attribute to the constant pool of this class.

code - the bytecode of the method corresponding to this code attribute, or null if this attribute is not a code attribute. Corresponds to the 'code' field of the Code attribute.

codeLength - the length of the bytecode of the method corresponding to this code attribute, or 0 if this attribute is not a code attribute. Corresponds to the 'code_length' field of the Code attribute.

maxStack - the maximum stack size of the method corresponding to this code attribute, or -1 if this attribute is not a code attribute.

maxLocals - the maximum number of local variables of the method corresponding to this code attribute, or -1 if this attribute is not a code attribute.

Returns:

the byte array form of this attribute.