org.objectweb.asm

Class MethodVisitor

java.lang.Object

org.objectweb.asm.MethodVisitor

Direct Known Subclasses:

AnalyzerAdapter, CheckMethodAdapter, CodeSizeEvaluator, InstructionAdapter, LocalVariablesSorter, MethodNode, SAXCodeAdapter, TraceMethodVisitor

public abstract class MethodVisitor
extends Object

A visitor to visit a Java method. The methods of this class must be called in the following order: [ visitAnnotationDefault ] ( visitAnnotation | visitParameterAnnotation | visitAttribute )* [ visitCode ( visitFrame | visitXInsn | visitLabel | visitTryCatchBlock | visitLocalVariable | visitLineNumber )* visitMaxs ] visitEnd. In addition, the visitXInsn and visitLabel methods must be called in the sequential order of the bytecode instructions of the visited code, visitTryCatchBlock must be called before the labels passed as arguments have been visited, and the visitLocalVariable and visitLineNumber methods must be called after the labels passed as arguments have been visited.

Author:

Eric Bruneton

Field Summary

Fields

Modifier and Type	Field and Description
protected int	api The ASM API version implemented by this visitor.
protected MethodVisitor	mv The method visitor to which this visitor must delegate method calls.

Constructor Summary

Constructors

Constructor and Description
MethodVisitor(int api) Constructs a new MethodVisitor.
MethodVisitor(int api, MethodVisitor mv) Constructs a new MethodVisitor.

Method Summary

Methods

Modifier and Type	Method and Description
AnnotationVisitor	visitAnnotation(String desc, boolean visible) Visits an annotation of this method.
AnnotationVisitor	visitAnnotationDefault() Visits the default value of this annotation interface method.
void	visitAttribute(Attribute attr) Visits a non standard attribute of this method.
void	visitCode() Starts the visit of the method's code, if any (i.e. non abstract method).
void	visitEnd() Visits the end of the method.
void	visitFieldInsn(int opcode, String owner, String name, String desc) Visits a field instruction.
void	visitFrame(int type, int nLocal, Object[] local, int nStack, Object[] stack) Visits the current state of the local variables and operand stack elements.
void	visitIincInsn(int var, int increment) Visits an IINC instruction.
void	visitInsn(int opcode) Visits a zero operand instruction.
void	visitIntInsn(int opcode, int operand) Visits an instruction with a single int operand.
void	visitInvokeDynamicInsn(String name, String desc, Handle bsm, Object... bsmArgs) Visits an invokedynamic instruction.
void	visitJumpInsn(int opcode, Label label) Visits a jump instruction.
void	visitLabel(Label label) Visits a label.
void	visitLdcInsn(Object cst) Visits a LDC instruction.
void	visitLineNumber(int line, Label start) Visits a line number declaration.
void	visitLocalVariable(String name, String desc, String signature, Label start, Label end, int index) Visits a local variable declaration.
void	visitLookupSwitchInsn(Label dflt, int[] keys, Label[] labels) Visits a LOOKUPSWITCH instruction.
void	visitMaxs(int maxStack, int maxLocals) Visits the maximum stack size and the maximum number of local variables of the method.
void	visitMethodInsn(int opcode, String owner, String name, String desc) Visits a method instruction.
void	visitMultiANewArrayInsn(String desc, int dims) Visits a MULTIANEWARRAY instruction.
AnnotationVisitor	visitParameterAnnotation(int parameter, String desc, boolean visible) Visits an annotation of a parameter this method.
void	visitTableSwitchInsn(int min, int max, Label dflt, Label... labels) Visits a TABLESWITCH instruction.
void	visitTryCatchBlock(Label start, Label end, Label handler, String type) Visits a try catch block.
void	visitTypeInsn(int opcode, String type) Visits a type instruction.
void	visitVarInsn(int opcode, int var) Visits a local variable instruction.

Methods inherited from class java.lang.Object

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

Field Detail

api

protected final int api

The ASM API version implemented by this visitor. The value of this field must be one of Opcodes.ASM4.

mv

protected MethodVisitor mv

The method visitor to which this visitor must delegate method calls. May be null.

Constructor Detail

MethodVisitor

public MethodVisitor(int api)

Constructs a new MethodVisitor.

Parameters:

api - the ASM API version implemented by this visitor. Must be one of Opcodes.ASM4.

MethodVisitor

public MethodVisitor(int api,
             MethodVisitor mv)

Constructs a new MethodVisitor.

Parameters:

api - the ASM API version implemented by this visitor. Must be one of Opcodes.ASM4.

mv - the method visitor to which this visitor must delegate method calls. May be null.

Method Detail

visitAnnotationDefault

public AnnotationVisitor visitAnnotationDefault()

Visits the default value of this annotation interface method.

Returns:

a visitor to the visit the actual default value of this annotation interface method, or null if this visitor is not interested in visiting this default value. The 'name' parameters passed to the methods of this annotation visitor are ignored. Moreover, exacly one visit method must be called on this annotation visitor, followed by visitEnd.

visitAnnotation

public AnnotationVisitor visitAnnotation(String desc,
                                boolean visible)

Visits an annotation of this method.

Parameters:

desc - the class descriptor of the annotation class.

visible - true if the annotation is visible at runtime.

Returns:

a visitor to visit the annotation values, or null if this visitor is not interested in visiting this annotation.

visitParameterAnnotation

public AnnotationVisitor visitParameterAnnotation(int parameter,
                                         String desc,
                                         boolean visible)

Visits an annotation of a parameter this method.

Parameters:

parameter - the parameter index.

desc - the class descriptor of the annotation class.

visible - true if the annotation is visible at runtime.

Returns:

a visitor to visit the annotation values, or null if this visitor is not interested in visiting this annotation.

visitAttribute

public void visitAttribute(Attribute attr)

Visits a non standard attribute of this method.

Parameters:

attr - an attribute.

visitCode

public void visitCode()

Starts the visit of the method's code, if any (i.e. non abstract method).

visitFrame

public void visitFrame(int type,
              int nLocal,
              Object[] local,
              int nStack,
              Object[] stack)

Visits the current state of the local variables and operand stack elements. This method must(*) be called just before any instruction i that follows an unconditional branch instruction such as GOTO or THROW, that is the target of a jump instruction, or that starts an exception handler block. The visited types must describe the values of the local variables and of the operand stack elements just before i is executed.

(*) this is mandatory only for classes whose version is greater than or equal to V1_6.

The frames of a method must be given either in expanded form, or in compressed form (all frames must use the same format, i.e. you must not mix expanded and compressed frames within a single method):

• In expanded form, all frames must have the F_NEW type.
• In compressed form, frames are basically "deltas" from the state of the previous frame:
  • Opcodes.F_SAME representing frame with exactly the same locals as the previous frame and with the empty stack.
  • Opcodes.F_SAME1 representing frame with exactly the same locals as the previous frame and with single value on the stack ( nStack is 1 and stack[0] contains value for the type of the stack item).
  • Opcodes.F_APPEND representing frame with current locals are the same as the locals in the previous frame, except that additional locals are defined (nLocal is 1, 2 or 3 and local elements contains values representing added types).
  • Opcodes.F_CHOP representing frame with current locals are the same as the locals in the previous frame, except that the last 1-3 locals are absent and with the empty stack (nLocals is 1, 2 or 3).
  • Opcodes.F_FULL representing complete frame data.

In both cases the first frame, corresponding to the method's parameters and access flags, is implicit and must not be visited. Also, it is illegal to visit two or more frames for the same code location (i.e., at least one instruction must be visited between two calls to visitFrame).

Parameters:

type - the type of this stack map frame. Must be Opcodes.F_NEW for expanded frames, or Opcodes.F_FULL, Opcodes.F_APPEND, Opcodes.F_CHOP, Opcodes.F_SAME or Opcodes.F_APPEND, Opcodes.F_SAME1 for compressed frames.

nLocal - the number of local variables in the visited frame.

local - the local variable types in this frame. This array must not be modified. Primitive types are represented by Opcodes.TOP, Opcodes.INTEGER, Opcodes.FLOAT, Opcodes.LONG, Opcodes.DOUBLE,Opcodes.NULL or Opcodes.UNINITIALIZED_THIS (long and double are represented by a single element). Reference types are represented by String objects (representing internal names), and uninitialized types by Label objects (this label designates the NEW instruction that created this uninitialized value).

nStack - the number of operand stack elements in the visited frame.

stack - the operand stack types in this frame. This array must not be modified. Its content has the same format as the "local" array.

Throws:

IllegalStateException - if a frame is visited just after another one, without any instruction between the two (unless this frame is a Opcodes#F_SAME frame, in which case it is silently ignored).

visitInsn

public void visitInsn(int opcode)

Visits a zero operand instruction.

Parameters:

opcode - the opcode of the instruction to be visited. This opcode is either NOP, ACONST_NULL, ICONST_M1, ICONST_0, ICONST_1, ICONST_2, ICONST_3, ICONST_4, ICONST_5, LCONST_0, LCONST_1, FCONST_0, FCONST_1, FCONST_2, DCONST_0, DCONST_1, IALOAD, LALOAD, FALOAD, DALOAD, AALOAD, BALOAD, CALOAD, SALOAD, IASTORE, LASTORE, FASTORE, DASTORE, AASTORE, BASTORE, CASTORE, SASTORE, POP, POP2, DUP, DUP_X1, DUP_X2, DUP2, DUP2_X1, DUP2_X2, SWAP, IADD, LADD, FADD, DADD, ISUB, LSUB, FSUB, DSUB, IMUL, LMUL, FMUL, DMUL, IDIV, LDIV, FDIV, DDIV, IREM, LREM, FREM, DREM, INEG, LNEG, FNEG, DNEG, ISHL, LSHL, ISHR, LSHR, IUSHR, LUSHR, IAND, LAND, IOR, LOR, IXOR, LXOR, I2L, I2F, I2D, L2I, L2F, L2D, F2I, F2L, F2D, D2I, D2L, D2F, I2B, I2C, I2S, LCMP, FCMPL, FCMPG, DCMPL, DCMPG, IRETURN, LRETURN, FRETURN, DRETURN, ARETURN, RETURN, ARRAYLENGTH, ATHROW, MONITORENTER, or MONITOREXIT.

visitIntInsn

public void visitIntInsn(int opcode,
                int operand)

Visits an instruction with a single int operand.

Parameters:

opcode - the opcode of the instruction to be visited. This opcode is either BIPUSH, SIPUSH or NEWARRAY.

operand - the operand of the instruction to be visited.
When opcode is BIPUSH, operand value should be between Byte.MIN_VALUE and Byte.MAX_VALUE.
When opcode is SIPUSH, operand value should be between Short.MIN_VALUE and Short.MAX_VALUE.
When opcode is NEWARRAY, operand value should be one of Opcodes.T_BOOLEAN, Opcodes.T_CHAR, Opcodes.T_FLOAT, Opcodes.T_DOUBLE, Opcodes.T_BYTE, Opcodes.T_SHORT, Opcodes.T_INT or Opcodes.T_LONG.

visitVarInsn

public void visitVarInsn(int opcode,
                int var)

Visits a local variable instruction. A local variable instruction is an instruction that loads or stores the value of a local variable.

Parameters:

opcode - the opcode of the local variable instruction to be visited. This opcode is either ILOAD, LLOAD, FLOAD, DLOAD, ALOAD, ISTORE, LSTORE, FSTORE, DSTORE, ASTORE or RET.

var - the operand of the instruction to be visited. This operand is the index of a local variable.

visitTypeInsn

public void visitTypeInsn(int opcode,
                 String type)

Visits a type instruction. A type instruction is an instruction that takes the internal name of a class as parameter.

Parameters:

opcode - the opcode of the type instruction to be visited. This opcode is either NEW, ANEWARRAY, CHECKCAST or INSTANCEOF.

type - the operand of the instruction to be visited. This operand must be the internal name of an object or array class (see getInternalName).

visitFieldInsn

public void visitFieldInsn(int opcode,
                  String owner,
                  String name,
                  String desc)

Visits a field instruction. A field instruction is an instruction that loads or stores the value of a field of an object.

Parameters:

opcode - the opcode of the type instruction to be visited. This opcode is either GETSTATIC, PUTSTATIC, GETFIELD or PUTFIELD.

owner - the internal name of the field's owner class (see getInternalName).

name - the field's name.

desc - the field's descriptor (see Type).

visitMethodInsn

public void visitMethodInsn(int opcode,
                   String owner,
                   String name,
                   String desc)

Visits a method instruction. A method instruction is an instruction that invokes a method.

Parameters:

opcode - the opcode of the type instruction to be visited. This opcode is either INVOKEVIRTUAL, INVOKESPECIAL, INVOKESTATIC or INVOKEINTERFACE.

owner - the internal name of the method's owner class (see getInternalName).

name - the method's name.

desc - the method's descriptor (see Type).

visitInvokeDynamicInsn

public void visitInvokeDynamicInsn(String name,
                          String desc,
                          Handle bsm,
                          Object... bsmArgs)

Visits an invokedynamic instruction.

Parameters:

name - the method's name.

desc - the method's descriptor (see Type).

bsm - the bootstrap method.

bsmArgs - the bootstrap method constant arguments. Each argument must be an Integer, Float, Long, Double, String, Type or Handle value. This method is allowed to modify the content of the array so a caller should expect that this array may change.

visitJumpInsn

public void visitJumpInsn(int opcode,
                 Label label)

Visits a jump instruction. A jump instruction is an instruction that may jump to another instruction.

Parameters:

opcode - the opcode of the type instruction to be visited. This opcode is either IFEQ, IFNE, IFLT, IFGE, IFGT, IFLE, IF_ICMPEQ, IF_ICMPNE, IF_ICMPLT, IF_ICMPGE, IF_ICMPGT, IF_ICMPLE, IF_ACMPEQ, IF_ACMPNE, GOTO, JSR, IFNULL or IFNONNULL.

label - the operand of the instruction to be visited. This operand is a label that designates the instruction to which the jump instruction may jump.

visitLabel

public void visitLabel(Label label)

Visits a label. A label designates the instruction that will be visited just after it.

Parameters:

label - a Label object.

visitLdcInsn

public void visitLdcInsn(Object cst)

Visits a LDC instruction. Note that new constant types may be added in future versions of the Java Virtual Machine. To easily detect new constant types, implementations of this method should check for unexpected constant types, like this:

 if (cst instanceof Integer) {
     // ...
 } else if (cst instanceof Float) {
     // ...
 } else if (cst instanceof Long) {
     // ...
 } else if (cst instanceof Double) {
     // ...
 } else if (cst instanceof String) {
     // ...
 } else if (cst instanceof Type) {
     int sort = ((Type) cst).getSort();
     if (sort == Type.OBJECT) {
         // ...
     } else if (sort == Type.ARRAY) {
         // ...
     } else if (sort == Type.METHOD) {
         // ...
     } else {
         // throw an exception
     }
 } else if (cst instanceof Handle) {
     // ...
 } else {
     // throw an exception
 }
 

Parameters:

cst - the constant to be loaded on the stack. This parameter must be a non null Integer, a Float, a Long, a Double, a String, a Type of OBJECT or ARRAY sort for .class constants, for classes whose version is 49.0, a Type of METHOD sort or a Handle for MethodType and MethodHandle constants, for classes whose version is 51.0.

visitIincInsn

public void visitIincInsn(int var,
                 int increment)

Visits an IINC instruction.

Parameters:

var - index of the local variable to be incremented.

increment - amount to increment the local variable by.

visitTableSwitchInsn

public void visitTableSwitchInsn(int min,
                        int max,
                        Label dflt,
                        Label... labels)

Visits a TABLESWITCH instruction.

Parameters:

min - the minimum key value.

max - the maximum key value.

dflt - beginning of the default handler block.

labels - beginnings of the handler blocks. labels[i] is the beginning of the handler block for the min + i key.

visitLookupSwitchInsn

public void visitLookupSwitchInsn(Label dflt,
                         int[] keys,
                         Label[] labels)

Visits a LOOKUPSWITCH instruction.

Parameters:

dflt - beginning of the default handler block.

keys - the values of the keys.

labels - beginnings of the handler blocks. labels[i] is the beginning of the handler block for the keys[i] key.

visitMultiANewArrayInsn

public void visitMultiANewArrayInsn(String desc,
                           int dims)

Visits a MULTIANEWARRAY instruction.

Parameters:

desc - an array type descriptor (see Type).

dims - number of dimensions of the array to allocate.

visitTryCatchBlock

public void visitTryCatchBlock(Label start,
                      Label end,
                      Label handler,
                      String type)

Visits a try catch block.

Parameters:

start - beginning of the exception handler's scope (inclusive).

end - end of the exception handler's scope (exclusive).

handler - beginning of the exception handler's code.

type - internal name of the type of exceptions handled by the handler, or null to catch any exceptions (for "finally" blocks).

Throws:

IllegalArgumentException - if one of the labels has already been visited by this visitor (by the visitLabel method).

visitLocalVariable

public void visitLocalVariable(String name,
                      String desc,
                      String signature,
                      Label start,
                      Label end,
                      int index)

Visits a local variable declaration.

Parameters:

name - the name of a local variable.

desc - the type descriptor of this local variable.

signature - the type signature of this local variable. May be null if the local variable type does not use generic types.

start - the first instruction corresponding to the scope of this local variable (inclusive).

end - the last instruction corresponding to the scope of this local variable (exclusive).

index - the local variable's index.

Throws:

IllegalArgumentException - if one of the labels has not already been visited by this visitor (by the visitLabel method).

visitLineNumber

public void visitLineNumber(int line,
                   Label start)

Visits a line number declaration.

Parameters:

line - a line number. This number refers to the source file from which the class was compiled.

start - the first instruction corresponding to this line number.

Throws:

IllegalArgumentException - if start has not already been visited by this visitor (by the visitLabel method).

visitMaxs

public void visitMaxs(int maxStack,
             int maxLocals)

Visits the maximum stack size and the maximum number of local variables of the method.

Parameters:

maxStack - maximum stack size of the method.

maxLocals - maximum number of local variables for the method.

visitEnd

public void visitEnd()

Visits the end of the method. This method, which is the last one to be called, is used to inform the visitor that all the annotations and attributes of the method have been visited.