# Package org.objectweb.asm.tree

Provides an ASM visitor that constructs a tree representation of the classes it visits.

See: Description

- Class Summary
  Class | Description
  --- | ---
  AbstractInsnNode | A node that represents a bytecode instruction.
  AnnotationNode | A node that represents an annotationn.
  ClassNode | A node that represents a class.
  FieldInsnNode | A node that represents a field instruction.
  FieldNode | A node that represents a field.
  FrameNode | A node that represents a stack map frame.
  IincInsnNode | A node that represents an IINC instruction.
  InnerClassNode | A node that represents an inner class.
  InsnList | A doubly linked list of `AbstractInsnNode` objects.
  InsnNode | A node that represents a zero operand instruction.
  IntInsnNode | A node that represents an instruction with a single int operand.
  InvokeDynamicInsnNode | A node that represents an invokedynamic instruction.
  JumpInsnNode | A node that represents a jump instruction.
  LabelNode | An `AbstractInsnNode` that encapsulates a `Label`.
  LdcInsnNode | A node that represents an LDC instruction.
  LineNumberNode | A node that represents a line number declaration.
  LocalVariableAnnotationNode | A node that represents a type annotation on a local or resource variable.
  LocalVariableNode | A node that represents a local variable declaration.
  LookupSwitchInsnNode | A node that represents a LOOKUPSWITCH instruction.
  MethodInsnNode | A node that represents a method instruction.
  MethodNode | A node that represents a method.
  MultiANewArrayInsnNode | A node that represents a MULTIANEWARRAY instruction.
  ParameterNode | A node that represents a parameter access and name.
  TableSwitchInsnNode | A node that represents a TABLESWITCH instruction.
  TryCatchBlockNode | A node that represents a try catch block.
  TypeAnnotationNode | A node that represents a type annotationn.
  TypeInsnNode | A node that represents a type instruction.
  VarInsnNode | A node that represents a local variable instruction.

## Package org.objectweb.asm.tree Description

Provides an ASM visitor that constructs a tree representation of the classes it visits. This class adapter can be useful to implement "complex" class manipulation operations, i.e., operations that would be very hard to implement without using a tree representation (such as optimizing the number of local variables used by a method).

However, this class adapter has a cost: it makes ASM bigger and slower. Indeed it requires more than twenty new classes, and multiplies the time needed to transform a class by almost two (it is almost two times faster to read, "modify" and write a class with a ClassVisitor than with a ClassNode). This is why this package is bundled in an optional `asm-tree.jar` library that is separated from (but requires) the `asm.jar` library, which contains the core ASM framework. This is also why it is recommended not to use this class adapter when it is possible.

The root class is the ClassNode, that can be created from existing bytecode. For example:

      ClassReader cr = new ClassReader(source);
      ClassNode cn = new ClassNode();
      cr.accept(cn, true);

Now the content of ClassNode can be modified and then serialized back into bytecode:

      ClassWriter cw = new ClassWriter(true);
      cn.accept(cw);

Using a simple ClassVisitor it is possible to create MethodNode instances per-method. In this example MethodNode is acting as a buffer that is flushed out at visitEnd() call:

      ClassReader cr = new ClassReader(source);
      ClassWriter cw = new ClassWriter();
      ClassVisitor cv = new ClassVisitor(cw) {
        public MethodVisitor visitMethod(int access, String name,
            String desc, String signature, String[] exceptions) {
          final MethodVisitor mv = super.visitMethod(access, name, desc, signature, exceptions);
          MethodNode mn = new MethodNode(access, name, desc, signature, exceptions) {
            public void visitEnd() {
              // transform or analyze method code using tree API
              accept(mv);
            }
          };
        }
      };
      cr.accept(cv, true);

Several strategies can be used to construct method code from scratch. The first option is to create a MethodNode, and then create XxxInsnNode instances and add them to the instructions list:

    MethodNode m = new MethodNode(...);
    m.instructions.add(new VarInsnNode(ALOAD, 0));
    ...

Alternatively, you can use the fact that MethodNode is a MethodVisitor, and use that to create the XxxInsnNode and add them to the instructions list through the standard MethodVisitor methods:

    MethodNode m = new MethodNode(...);
    m.visitVarInsn(ALOAD, 0);
    ...

If you cannot generate all the instructions in sequential order, i.e. if you need to save some pointer in the instruction list and then insert instructions at that place after other instructions have been generated, you can use InsnList methods insert() and insertBefore() to insert instructions at a saved pointer.

    MethodNode m = new MethodNode(...);
    m.visitVarInsn(ALOAD, 0);
    AbstractInsnNode ptr = m.instructions.getLast();
    m.visitVarInsn(ALOAD, 1);
    // inserts an instruction between ALOAD 0 and ALOAD 1
    m.instructions.insert(ptr, new VarInsnNode(ALOAD, 0));
    ...

If you need to insert instructions while iterating over an existing instruction list, you can also use several strategies. The first one is to use a ListIterator over the instruction list:

    ListIterator it = m.instructions.iterator();
    while (it.hasNext()) {
        AbstractInsnNode n = (AbstractInsnNode) it.next();
        if (...) {
            it.add(new VarInsnNode(ALOAD, 0));
        }
    }

It is also possible to convert an instruction list into an array and iterate trough array elements:

    AbstractInsnNode[] insns = m.instructions.toArray();
    for(int i = 0; i<insns.length; i++) {
        AbstractInsnNode n = insns[i];
        if (...) {
            m.instructions.insert(n, new VarInsnNode(ALOAD, 0));
        }
    }

If you want to insert these instructions through the MethodVisitor methods, you can use another instance of MethodNode as a MethodVisitor and then insert instructions collected by that instance into the instruction list. For example:

    AbstractInsnNode[] insns = m.instructions.toArray();
    for(int i = 0; i<insns.length; i++) {
        AbstractInsnNode n = insns[i];
        if (...) {
            MethodNode mn = new MethodNode();
            mn.visitVarInsn(ALOAD, 0);
            mn.visitVarInsn(ALOAD, 1);
            m.instructions.insert(n, mn.instructions);
        }
    }

Since:
  ASM 1.3.3