org.objectweb.asm
Class CodeWriter

java.lang.Object
  extended by org.objectweb.asm.CodeWriter
All Implemented Interfaces:
CodeVisitor

public class CodeWriter
extends Object
implements CodeVisitor

A CodeVisitor that generates Java bytecode instructions. Each visit method of this class appends the bytecode corresponding to the visited instruction to a byte vector, in the order these methods are called.

Author:
Eric Bruneton

Constructor Summary
protected CodeWriter(ClassWriter cw, boolean computeMaxs)
          Constructs a CodeWriter.
 
Method Summary
 byte[] getCode()
          Returns the current bytecode of this method.
 int getCodeSize()
          Returns the current size of the bytecode of this method.
protected  void init(int access, String name, String desc, String[] exceptions, Attribute attrs)
          Initializes this CodeWriter to define the bytecode of the specified method.
protected  int[] resizeInstructions(int[] indexes, int[] sizes, int len)
          Resizes the designated instructions, while keeping jump offsets and instruction addresses consistent.
 void visitAttribute(Attribute attr)
          Visits a non standard attribute of the code.
 void visitFieldInsn(int opcode, String owner, String name, String desc)
          Visits a field instruction.
 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 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, 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.
 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 desc)
          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
 

Constructor Detail

CodeWriter

protected CodeWriter(ClassWriter cw,
                     boolean computeMaxs)
Constructs a CodeWriter.

Parameters:
cw - the class writer in which the method must be added.
computeMaxs - true if the maximum stack size and number of local variables must be automatically computed.
Method Detail

init

protected void init(int access,
                    String name,
                    String desc,
                    String[] exceptions,
                    Attribute attrs)
Initializes this CodeWriter to define the bytecode of the specified method.

Parameters:
access - the method's access flags (see Constants).
name - the method's name.
desc - the method's descriptor (see Type).
exceptions - the internal names of the method's exceptions. May be null.
attrs - the non standard attributes of the method.

visitInsn

public void visitInsn(int opcode)
Description copied from interface: CodeVisitor
Visits a zero operand instruction.

Specified by:
visitInsn in interface CodeVisitor
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)
Description copied from interface: CodeVisitor
Visits an instruction with a single int operand.

Specified by:
visitIntInsn in interface CodeVisitor
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.

visitVarInsn

public void visitVarInsn(int opcode,
                         int var)
Description copied from interface: CodeVisitor
Visits a local variable instruction. A local variable instruction is an instruction that loads or stores the value of a local variable.

Specified by:
visitVarInsn in interface CodeVisitor
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 desc)
Description copied from interface: CodeVisitor
Visits a type instruction. A type instruction is an instruction that takes a type descriptor as parameter.

Specified by:
visitTypeInsn in interface CodeVisitor
Parameters:
opcode - the opcode of the type instruction to be visited. This opcode is either NEW, ANEWARRAY, CHECKCAST or INSTANCEOF.
desc - the operand of the instruction to be visited. This operand is must be a fully qualified class name in internal form, or the type descriptor of an array type (see Type).

visitFieldInsn

public void visitFieldInsn(int opcode,
                           String owner,
                           String name,
                           String desc)
Description copied from interface: CodeVisitor
Visits a field instruction. A field instruction is an instruction that loads or stores the value of a field of an object.

Specified by:
visitFieldInsn in interface CodeVisitor
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)
Description copied from interface: CodeVisitor
Visits a method instruction. A method instruction is an instruction that invokes a method.

Specified by:
visitMethodInsn in interface CodeVisitor
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).

visitJumpInsn

public void visitJumpInsn(int opcode,
                          Label label)
Description copied from interface: CodeVisitor
Visits a jump instruction. A jump instruction is an instruction that may jump to another instruction.

Specified by:
visitJumpInsn in interface CodeVisitor
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)
Description copied from interface: CodeVisitor
Visits a label. A label designates the instruction that will be visited just after it.

Specified by:
visitLabel in interface CodeVisitor
Parameters:
label - a Label object.

visitLdcInsn

public void visitLdcInsn(Object cst)
Description copied from interface: CodeVisitor
Visits a LDC instruction.

Specified by:
visitLdcInsn in interface CodeVisitor
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 (or a Type for .class constants, for classes whose version is 49.0 or more).

visitIincInsn

public void visitIincInsn(int var,
                          int increment)
Description copied from interface: CodeVisitor
Visits an IINC instruction.

Specified by:
visitIincInsn in interface CodeVisitor
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)
Description copied from interface: CodeVisitor
Visits a TABLESWITCH instruction.

Specified by:
visitTableSwitchInsn in interface CodeVisitor
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)
Description copied from interface: CodeVisitor
Visits a LOOKUPSWITCH instruction.

Specified by:
visitLookupSwitchInsn in interface CodeVisitor
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)
Description copied from interface: CodeVisitor
Visits a MULTIANEWARRAY instruction.

Specified by:
visitMultiANewArrayInsn in interface CodeVisitor
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)
Description copied from interface: CodeVisitor
Visits a try catch block.

Specified by:
visitTryCatchBlock in interface CodeVisitor
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).

visitMaxs

public void visitMaxs(int maxStack,
                      int maxLocals)
Description copied from interface: CodeVisitor
Visits the maximum stack size and the maximum number of local variables of the method.

Specified by:
visitMaxs in interface CodeVisitor
Parameters:
maxStack - maximum stack size of the method.
maxLocals - maximum number of local variables for the method.

visitLocalVariable

public void visitLocalVariable(String name,
                               String desc,
                               Label start,
                               Label end,
                               int index)
Description copied from interface: CodeVisitor
Visits a local variable declaration.

Specified by:
visitLocalVariable in interface CodeVisitor
Parameters:
name - the name of a local variable.
desc - the type descriptor of this local variable.
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.

visitLineNumber

public void visitLineNumber(int line,
                            Label start)
Description copied from interface: CodeVisitor
Visits a line number declaration.

Specified by:
visitLineNumber in interface CodeVisitor
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.

visitAttribute

public void visitAttribute(Attribute attr)
Description copied from interface: CodeVisitor
Visits a non standard attribute of the code. This method must visit only the first attribute in the given attribute list.

Specified by:
visitAttribute in interface CodeVisitor
Parameters:
attr - a non standard code attribute. Must not be null.

resizeInstructions

protected int[] resizeInstructions(int[] indexes,
                                   int[] sizes,
                                   int len)
Resizes the designated instructions, while keeping jump offsets and instruction addresses consistent. This may require to resize other existing instructions, or even to introduce new instructions: for example, increasing the size of an instruction by 2 at the middle of a method can increases the offset of an IFEQ instruction from 32766 to 32768, in which case IFEQ 32766 must be replaced with IFNEQ 8 GOTO_W 32765. This, in turn, may require to increase the size of another jump instruction, and so on... All these operations are handled automatically by this method.

This method must be called after all the method that is being built has been visited. In particular, the Label objects used to construct the method are no longer valid after this method has been called.

Parameters:
indexes - current positions of the instructions to be resized. Each instruction must be designated by the index of its last byte, plus one (or, in other words, by the index of the first byte of the next instruction).
sizes - the number of bytes to be added to the above instructions. More precisely, for each i < len, sizes[i] bytes will be added at the end of the instruction designated by indexes[i] or, if sizes[i] is negative, the last |sizes[i]| bytes of the instruction will be removed (the instruction size must not become negative or null). The gaps introduced by this method must be filled in "manually" in the array returned by the getCode method.
len - the number of instruction to be resized. Must be smaller than or equal to indexes.length and sizes.length.
Returns:
the indexes array, which now contains the new positions of the resized instructions (designated as above).

getCodeSize

public int getCodeSize()
Returns the current size of the bytecode of this method. This size just includes the size of the bytecode instructions: it does not include the size of the Exceptions, LocalVariableTable, LineNumberTable, Synthetic and Deprecated attributes, if present.

Returns:
the current size of the bytecode of this method.

getCode

public byte[] getCode()
Returns the current bytecode of this method. This bytecode only contains the instructions: it does not include the Exceptions, LocalVariableTable, LineNumberTable, Synthetic and Deprecated attributes, if present.

Returns:
the current bytecode of this method. The bytecode is contained between the index 0 (inclusive) and the index getCodeSize (exclusive).