gt:         if (opcode == null)
context: /*
   * Copyright (c) 2009, 2013, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package com.sun.tools.classfile;
  
  import java.util.Locale;
  
  /**
   * See JVMS, chapter 6.
   *
   *  <p><b>This is NOT part of any supported API.
   *  If you write code that depends on this, you do so at your own risk.
   *  This code and its internal interfaces are subject to change or
   *  deletion without notice.</b>
   *
   * @see Code_attribute#getInstructions
   */
  public class Instruction {
      /** The kind of an instruction, as determined by the position, size and
       *  types of its operands. */
      public static enum Kind {
          /** Opcode is not followed by any operands. */
          NO_OPERANDS(1),
          /** Opcode is followed by a byte indicating a type. */
          ATYPE(2),
          /** Opcode is followed by a 2-byte branch offset. */
          BRANCH(3),
          /** Opcode is followed by a 4-byte branch offset. */
          BRANCH_W(5),
          /** Opcode is followed by a signed byte value. */
          BYTE(2),
          /** Opcode is followed by a 1-byte index into the constant pool. */
          CPREF(2),
          /** Opcode is followed by a 2-byte index into the constant pool. */
          CPREF_W(3),
          /** Opcode is followed by a 2-byte index into the constant pool,
           *  an unsigned byte value. */
          CPREF_W_UBYTE(4),
          /** Opcode is followed by a 2-byte index into the constant pool.,
           *  an unsigned byte value, and a zero byte. */
          CPREF_W_UBYTE_ZERO(5),
          /** Opcode is followed by variable number of operands, depending
           * on the instruction.*/
          DYNAMIC(-1),
          /** Opcode is followed by a 1-byte reference to a local variable. */
          LOCAL(2),
          /** Opcode is followed by a 1-byte reference to a local variable,
           *  and a signed byte value. */
          LOCAL_BYTE(3),
          /** Opcode is followed by a signed short value. */
          SHORT(3),
          /** Wide opcode is not followed by any operands. */
          WIDE_NO_OPERANDS(2),
          /** Wide opcode is followed by a 2-byte index into the local variables array. */
          WIDE_LOCAL(4),
          /** Wide opcode is followed by a 2-byte index into the constant pool. */
          WIDE_CPREF_W(4),
          /** Wide opcode is followed by a 2-byte index into the constant pool,
           *  and a signed short value. */
          WIDE_CPREF_W_SHORT(6),
          /** Wide opcode is followed by a 2-byte reference to a local variable,
           *  and a signed short value. */
          WIDE_LOCAL_SHORT(6),
          /** Opcode was not recognized. */
          UNKNOWN(1);
  
          Kind(int length) {
              this.length = length;
          }
  
          /** The length, in bytes, of this kind of instruction, or -1 is the
           *  length depends on the specific instruction. */
          public final int length;
      }
  
      /** A utility visitor to help decode the operands of an instruction.
       *  @see Instruction#accept */
      public interface KindVisitor<R,P> {
          /** See {@link Kind#NO_OPERANDS}, {@link Kind#WIDE_NO_OPERANDS}. */
          R visitNoOperands(Instruction instr, P p);
          /** See {@link Kind#ATYPE}. */
          R visitArrayType(Instruction instr, TypeKind kind, P p);
          /** See {@link Kind#BRANCH}, {@link Kind#BRANCH_W}. */
          R visitBranch(Instruction instr, int offset, P p);
          /** See {@link Kind#CPREF}, {@link Kind#CPREF_W}, {@link Kind#WIDE_CPREF_W}. */
          R visitConstantPoolRef(Instruction instr, int index, P p);
          /** See {@link Kind#CPREF_W_UBYTE}, {@link Kind#CPREF_W_UBYTE_ZERO}, {@link Kind#WIDE_CPREF_W_SHORT}. */
          R visitConstantPoolRefAndValue(Instruction instr, int index, int value, P p);
          /** See {@link Kind#LOCAL}, {@link Kind#WIDE_LOCAL}. */
          R visitLocal(Instruction instr, int index, P p);
          /** See {@link Kind#LOCAL_BYTE}. */
          R visitLocalAndValue(Instruction instr, int index, int value, P p);
          /** See {@link Kind#DYNAMIC}. */
          R visitLookupSwitch(Instruction instr, int default_, int npairs, int[] matches, int[] offsets, P p);
          /** See {@link Kind#DYNAMIC}. */
          R visitTableSwitch(Instruction instr, int default_, int low, int high, int[] offsets, P p);
          /** See {@link Kind#BYTE}, {@link Kind#SHORT}. */
          R visitValue(Instruction instr, int value, P p);
          /** Instruction is unrecognized. */
          R visitUnknown(Instruction instr, P p);
  
      }
  
      /** The kind of primitive array type to create.
       *  See JVMS chapter 6, newarray. */
      public static enum TypeKind {
          T_BOOLEAN(4, "boolean"),
          T_CHAR(5, "char"),
          T_FLOAT(6, "float"),
          T_DOUBLE(7, "double"),
          T_BYTE(8, "byte"),
          T_SHORT(9, "short"),
          T_INT (10, "int"),
          T_LONG (11, "long");
          TypeKind(int value, String name) {
              this.value = value;
              this.name = name;
          }
  
          public static TypeKind get(int value) {
              switch (value) {
                  case  4: return T_BOOLEAN;
                  case  5: return T_CHAR;
                  case  6: return T_FLOAT;
                  case  7: return T_DOUBLE;
                  case  8: return T_BYTE;
                  case  9: return T_SHORT;
                  case  10: return T_INT;
                  case  11: return T_LONG;
                  default: return null;
              }
          }
  
          public final int value;
          public final String name;
      }
  
      /** An instruction is defined by its position in a bytecode array. */
      public Instruction(byte[] bytes, int pc) {
          this.bytes = bytes;
          this.pc = pc;
      }
  
      /** Get the position of the instruction within the bytecode array. */
      public int getPC() {
          return pc;
      }
  
      /** Get a byte value, relative to the start of this instruction. */
      public int getByte(int offset) {
          return bytes[pc + offset];
      }
  
      /** Get an unsigned byte value, relative to the start of this instruction. */
      public int getUnsignedByte(int offset) {
          return getByte(offset) & 0xff;
      }
  
      /** Get a 2-byte value, relative to the start of this instruction. */
      public int getShort(int offset) {
          return (getByte(offset) << 8) | getUnsignedByte(offset + 1);
      }
  
      /** Get a unsigned 2-byte value, relative to the start of this instruction. */
      public int getUnsignedShort(int offset) {
          return getShort(offset) & 0xFFFF;
      }
  
      /** Get a 4-byte value, relative to the start of this instruction. */
      public int getInt(int offset) {
          return (getShort(offset) << 16) | (getUnsignedShort(offset + 2));
      }
  
      /** Get the Opcode for this instruction, or null if the instruction is
       * unrecognized. */
      public Opcode getOpcode() {
          int b = getUnsignedByte(0);
          switch (b) {
              case Opcode.NONPRIV:
              case Opcode.PRIV:
              case Opcode.WIDE:
                  return Opcode.get(b, getUnsignedByte(1));
          }
          return Opcode.get(b);
      }
  
      /** Get the mnemonic for this instruction, or a default string if the
       * instruction is unrecognized. */
      public String getMnemonic() {
          Opcode opcode = getOpcode();
  