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ClassReader.javaAPI DocGlassfish v2 API34994Thu Mar 02 11:51:12 GMT 2006oracle.toplink.libraries.asm

ClassReader

public class ClassReader extends Object
A Java class parser to make a {@link ClassVisitor ClassVisitor} visit an existing class. This class parses a byte array conforming to the Java class file format and calls the appropriate visit methods of a given class visitor for each field, method and bytecode instruction encountered.
author
Eric Bruneton

Fields Summary
public final byte[]
b
The class to be parsed. The content of this array must not be modified. This field is intended for {@link Attribute} sub classes, and is normally not needed by class generators or adapters.
private int[]
items
The start index of each constant pool item in {@link #b b}, plus one. The one byte offset skips the constant pool item tag that indicates its type.
private String[]
strings
The String objects corresponding to the CONSTANT_Utf8 items. This cache avoids multiple parsing of a given CONSTANT_Utf8 constant pool item, which GREATLY improves performances (by a factor 2 to 3). This caching strategy could be extended to all constant pool items, but its benefit would not be so great for these items (because they are much less expensive to parse than CONSTANT_Utf8 items).
private int
maxStringLength
Maximum length of the strings contained in the constant pool of the class.
private int
header
Start index of the class header information (access, name...) in {@link #b b}.
Constructors Summary
public ClassReader(byte[] b)
Constructs a new {@link ClassReader ClassReader} object.

param
b the bytecode of the class to be read.

    this(b, 0, b.length);
public ClassReader(byte[] b, int off, int len)
Constructs a new {@link ClassReader ClassReader} object.

param
b the bytecode of the class to be read.
param
off the start offset of the class data.
param
len the length of the class data.

    this.b = b;
    // parses the constant pool
    items = new int[readUnsignedShort(off + 8)];
    strings = new String[items.length];
    int max = 0;
    int index = off + 10;
    for (int i = 1; i < items.length; ++i) {
      items[i] = index + 1;
      int tag = b[index];
      int size;
      switch (tag) {
        case ClassWriter.FIELD:
        case ClassWriter.METH:
        case ClassWriter.IMETH:
        case ClassWriter.INT:
        case ClassWriter.FLOAT:
        case ClassWriter.NAME_TYPE:
          size = 5;
          break;
        case ClassWriter.LONG:
        case ClassWriter.DOUBLE:
          size = 9;
          ++i;
          break;
        case ClassWriter.UTF8:
          size = 3 + readUnsignedShort(index + 1);
          max = (size > max ? size : max);
          break;
        //case ClassWriter.CLASS:
        //case ClassWriter.STR:
        default:
          size = 3;
          break;
      }
      index += size;
    }
    maxStringLength = max;
    // the class header information starts just after the constant pool
    header = index;
public ClassReader(InputStream is)
Constructs a new {@link ClassReader ClassReader} object.

param
is an input stream from which to read the class.
throws
IOException if a problem occurs during reading.

    this(readClass(is));
public ClassReader(String name)
Constructs a new {@link ClassReader ClassReader} object.

param
name the fully qualified name of the class to be read.
throws
IOException if an exception occurs during reading.

    this(ClassLoader.getSystemResourceAsStream(name.replace('.",'/") + ".class"));
Methods Summary
public voidaccept(oracle.toplink.libraries.asm.ClassVisitor classVisitor, boolean skipDebug)
Makes the given visitor visit the Java class of this {@link ClassReader ClassReader}. This class is the one specified in the constructor (see {@link #ClassReader(byte[]) ClassReader}).

param
classVisitor the visitor that must visit this class.
param
skipDebug true if the debug information of the class must not be visited. In this case the {@link CodeVisitor#visitLocalVariable visitLocalVariable} and {@link CodeVisitor#visitLineNumber visitLineNumber} methods will not be called.

    accept(classVisitor, new Attribute[0], skipDebug);
public voidaccept(oracle.toplink.libraries.asm.ClassVisitor classVisitor, oracle.toplink.libraries.asm.Attribute[] attrs, boolean skipDebug)
Makes the given visitor visit the Java class of this {@link ClassReader ClassReader}. This class is the one specified in the constructor (see {@link #ClassReader(byte[]) ClassReader}).

param
classVisitor the visitor that must visit this class.
param
attrs prototypes of the attributes that must be parsed during the visit of the class. Any attribute whose type is not equal to the type of one the prototypes will be ignored.
param
skipDebug true if the debug information of the class must not be visited. In this case the {@link CodeVisitor#visitLocalVariable visitLocalVariable} and {@link CodeVisitor#visitLineNumber visitLineNumber} methods will not be called.

    byte[] b = this.b;                     // the bytecode array
    char[] c = new char[maxStringLength];  // buffer used to read strings
    int i, j, k;                           // loop variables
    int u, v, w;                           // indexes in b
    Attribute attr;

    // visits the header
    u = header;
    int version = readInt(4);
    int access = readUnsignedShort(u);
    String className = readClass(u + 2, c);
    v = items[readUnsignedShort(u + 4)];
    String superClassName = v == 0 ? null : readUTF8(v, c);
    String[] implementedItfs = new String[readUnsignedShort(u + 6)];
    String sourceFile = null;
    Attribute clattrs = null;
    w = 0;
    u += 8;
    for (i = 0; i < implementedItfs.length; ++i) {
      implementedItfs[i] = readClass(u, c); u += 2;
    }
    // skips fields and methods
    v = u;
    i = readUnsignedShort(v); v += 2;
    for ( ; i > 0; --i) {
      j = readUnsignedShort(v + 6);
      v += 8;
      for ( ; j > 0; --j) {
        v += 6 + readInt(v + 2);
      }
    }
    i = readUnsignedShort(v); v += 2;
    for ( ; i > 0; --i) {
      j = readUnsignedShort(v + 6);
      v += 8;
      for ( ; j > 0; --j) {
        v += 6 + readInt(v + 2);
      }
    }
    // reads the class's attributes
    i = readUnsignedShort(v); v += 2;
    for ( ; i > 0; --i) {
      String attrName = readUTF8(v, c);
      if (attrName.equals("SourceFile")) {
        sourceFile = readUTF8(v + 6, c);
      } else if (attrName.equals("Deprecated")) {
        access |= Constants.ACC_DEPRECATED;
      } else if (attrName.equals("Synthetic")) {
        access |= Constants.ACC_SYNTHETIC;
      } else if (attrName.equals("InnerClasses")) {
        w = v + 6;
      } else {
        attr = readAttribute(
            attrs, attrName, v + 6, readInt(v + 2), c, -1, null);
        if (attr != null) {
          attr.next = clattrs;
          clattrs = attr;
        }
      }
      v += 6 + readInt(v + 2);
    }
    // calls the visit method
    classVisitor.visit(
      version, access, className, superClassName, implementedItfs, sourceFile);

    // visits the inner classes info
    if (w != 0) {
      i = readUnsignedShort(w); w += 2;
      for ( ; i > 0; --i) {
        classVisitor.visitInnerClass(
          readUnsignedShort(w) == 0 ? null : readClass(w, c),
          readUnsignedShort(w + 2) == 0 ? null : readClass(w + 2, c),
          readUnsignedShort(w + 4) == 0 ? null : readUTF8(w + 4, c),
          readUnsignedShort(w + 6));
        w += 8;
      }
    }

    // visits the fields
    i = readUnsignedShort(u); u += 2;
    for ( ; i > 0; --i) {
      access = readUnsignedShort(u);
      String fieldName = readUTF8(u + 2, c);
      String fieldDesc = readUTF8(u + 4, c);
      Attribute fattrs = null;
      // visits the field's attributes and looks for a ConstantValue attribute
      int fieldValueItem = 0;
      j = readUnsignedShort(u + 6);
      u += 8;
      for ( ; j > 0; --j) {
        String attrName = readUTF8(u, c);
        if (attrName.equals("ConstantValue")) {
          fieldValueItem = readUnsignedShort(u + 6);
        } else if (attrName.equals("Synthetic")) {
          access |= Constants.ACC_SYNTHETIC;
        } else if (attrName.equals("Deprecated")) {
          access |= Constants.ACC_DEPRECATED;
        } else {
          attr = readAttribute(
            attrs, attrName, u + 6, readInt(u + 2), c, -1, null);
          if (attr != null) {
            attr.next = fattrs;
            fattrs = attr;
          }
        }
        u += 6 + readInt(u + 2);
      }
      // reads the field's value, if any
      Object value = (fieldValueItem == 0 ? null : readConst(fieldValueItem, c));
      // visits the field
      classVisitor.visitField(access, fieldName, fieldDesc, value, fattrs);
    }

    // visits the methods
    i = readUnsignedShort(u); u += 2;
    for ( ; i > 0; --i) {
      access = readUnsignedShort(u);
      String methName = readUTF8(u + 2, c);
      String methDesc = readUTF8(u + 4, c);
      Attribute mattrs = null;
      Attribute cattrs = null;
      v = 0;
      w = 0;
      // looks for Code and Exceptions attributes
      j = readUnsignedShort(u + 6);
      u += 8;
      for ( ; j > 0; --j) {
        String attrName = readUTF8(u, c); u += 2;
        int attrSize = readInt(u); u += 4;
        if (attrName.equals("Code")) {
          v = u;
        } else if (attrName.equals("Exceptions")) {
          w = u;
        } else if (attrName.equals("Synthetic")) {
          access |= Constants.ACC_SYNTHETIC;
        } else if (attrName.equals("Deprecated")) {
          access |= Constants.ACC_DEPRECATED;
        } else {
          attr = readAttribute(attrs, attrName, u, attrSize, c, -1, null);
          if (attr != null) {
            attr.next = mattrs;
            mattrs = attr;
          }
        }
        u += attrSize;
      }
      // reads declared exceptions
      String[] exceptions;
      if (w == 0) {
        exceptions = null;
      } else {
        exceptions = new String[readUnsignedShort(w)]; w += 2;
        for (j = 0; j < exceptions.length; ++j) {
          exceptions[j] = readClass(w, c); w += 2;
        }
      }

      // visits the method's code, if any
      CodeVisitor cv;
      cv = classVisitor.visitMethod(
        access, methName, methDesc, exceptions, mattrs);
      if (cv != null && v != 0) {
        int maxStack = readUnsignedShort(v);
        int maxLocals = readUnsignedShort(v + 2);
        int codeLength = readInt(v + 4);
        v += 8;

        int codeStart = v;
        int codeEnd = v + codeLength;

        // 1st phase: finds the labels
        int label;
        Label[] labels = new Label[codeLength + 1];
        while (v < codeEnd) {
          int opcode = b[v] & 0xFF;
          switch (ClassWriter.TYPE[opcode]) {
            case ClassWriter.NOARG_INSN:
            case ClassWriter.IMPLVAR_INSN:
              v += 1;
              break;
            case ClassWriter.LABEL_INSN:
              label = v - codeStart + readShort(v + 1);
              if (labels[label] == null) {
                labels[label] = new Label();
              }
              v += 3;
              break;
            case ClassWriter.LABELW_INSN:
              label = v - codeStart + readInt(v + 1);
              if (labels[label] == null) {
                labels[label] = new Label();
              }
              v += 5;
              break;
            case ClassWriter.WIDE_INSN:
              opcode = b[v + 1] & 0xFF;
              if (opcode == Constants.IINC) {
                v += 6;
              } else {
                v += 4;
              }
              break;
            case ClassWriter.TABL_INSN:
              // skips 0 to 3 padding bytes
              w = v - codeStart;
              v = v + 4 - (w & 3);
              // reads instruction
              label = w + readInt(v); v += 4;
              if (labels[label] == null) {
                labels[label] = new Label();
              }
              j = readInt(v); v += 4;
              j = readInt(v) - j + 1; v += 4;
              for ( ; j > 0; --j) {
                label = w + readInt(v); v += 4;
                if (labels[label] == null) {
                  labels[label] = new Label();
                }
              }
              break;
            case ClassWriter.LOOK_INSN:
              // skips 0 to 3 padding bytes
              w = v - codeStart;
              v = v + 4 - (w & 3);
              // reads instruction
              label = w + readInt(v); v += 4;
              if (labels[label] == null) {
                labels[label] = new Label();
              }
              j = readInt(v); v += 4;
              for ( ; j > 0; --j) {
                v += 4; // skips key
                label = w + readInt(v); v += 4;
                if (labels[label] == null) {
                  labels[label] = new Label();
                }
              }
              break;
            case ClassWriter.VAR_INSN:
            case ClassWriter.SBYTE_INSN:
            case ClassWriter.LDC_INSN:
              v += 2;
              break;
            case ClassWriter.SHORT_INSN:
            case ClassWriter.LDCW_INSN:
            case ClassWriter.FIELDORMETH_INSN:
            case ClassWriter.TYPE_INSN:
            case ClassWriter.IINC_INSN:
              v += 3;
              break;
            case ClassWriter.ITFMETH_INSN:
              v += 5;
              break;
            // case MANA_INSN:
            default:
              v += 4;
              break;
          }
        }
        // parses the try catch entries
        j = readUnsignedShort(v); v += 2;
        for ( ; j > 0; --j) {
          label = readUnsignedShort(v);
          if (labels[label] == null) {
            labels[label] = new Label();
          }
          label = readUnsignedShort(v + 2);
          if (labels[label] == null) {
            labels[label] = new Label();
          }
          label = readUnsignedShort(v + 4);
          if (labels[label] == null) {
            labels[label] = new Label();
          }
          v += 8;
        }
        // parses the local variable, line number tables, and code attributes
        j = readUnsignedShort(v); v += 2;
        for ( ; j > 0; --j) {
          String attrName = readUTF8(v, c);
          if (attrName.equals("LocalVariableTable")) {
            if (!skipDebug) {
              k = readUnsignedShort(v + 6);
              w = v + 8;
              for ( ; k > 0; --k) {
                label = readUnsignedShort(w);
                if (labels[label] == null) {
                  labels[label] = new Label();
                }
                label += readUnsignedShort(w + 2);
                if (labels[label] == null) {
                  labels[label] = new Label();
                }
                w += 10;
              }
            }
          } else if (attrName.equals("LineNumberTable")) {
            if (!skipDebug) {
              k = readUnsignedShort(v + 6);
              w = v + 8;
              for ( ; k > 0; --k) {
                label = readUnsignedShort(w);
                if (labels[label] == null) {
                  labels[label] = new Label();
                }
                labels[label].line = readUnsignedShort(w + 2);
                w += 4;
              }
            }
          } else {
            for (k = 0; k < attrs.length; ++k) {
              if (attrs[k].type.equals(attrName)) {
                attr = attrs[k].read(
                  this, v + 6, readInt(v + 2), c, codeStart - 8, labels);
                if (attr != null) {
                  attr.next = cattrs;
                  cattrs = attr;
                }
              }
            }
          }
          v += 6 + readInt(v + 2);
        }

        // 2nd phase: visits each instruction
        v = codeStart;
        Label l;
        while (v < codeEnd) {
          w = v - codeStart;
          l = labels[w];
          if (l != null) {
            cv.visitLabel(l);
            if (!skipDebug && l.line > 0) {
              cv.visitLineNumber(l.line, l);
            }
          }
          int opcode = b[v] & 0xFF;
          switch (ClassWriter.TYPE[opcode]) {
            case ClassWriter.NOARG_INSN:
              cv.visitInsn(opcode);
              v += 1;
              break;
            case ClassWriter.IMPLVAR_INSN:
              if (opcode > Constants.ISTORE) {
                opcode -= 59; //ISTORE_0
                cv.visitVarInsn(Constants.ISTORE + (opcode >> 2), opcode & 0x3);
              } else {
                opcode -= 26; //ILOAD_0
                cv.visitVarInsn(Constants.ILOAD + (opcode >> 2), opcode & 0x3);
              }
              v += 1;
              break;
            case ClassWriter.LABEL_INSN:
              cv.visitJumpInsn(opcode, labels[w + readShort(v + 1)]);
              v += 3;
              break;
            case ClassWriter.LABELW_INSN:
              cv.visitJumpInsn(opcode - 33, labels[w + readInt(v + 1)]);
              v += 5;
              break;
            case ClassWriter.WIDE_INSN:
              opcode = b[v + 1] & 0xFF;
              if (opcode == Constants.IINC) {
                cv.visitIincInsn(readUnsignedShort(v + 2), readShort(v + 4));
                v += 6;
              } else {
                cv.visitVarInsn(opcode, readUnsignedShort(v + 2));
                v += 4;
              }
              break;
            case ClassWriter.TABL_INSN:
              // skips 0 to 3 padding bytes
              v = v + 4 - (w & 3);
              // reads instruction
              label = w + readInt(v); v += 4;
              int min = readInt(v); v += 4;
              int max = readInt(v); v += 4;
              Label[] table = new Label[max - min + 1];
              for (j = 0; j < table.length; ++j) {
                table[j] = labels[w + readInt(v)];
                v += 4;
              }
              cv.visitTableSwitchInsn(min, max, labels[label], table);
              break;
            case ClassWriter.LOOK_INSN:
              // skips 0 to 3 padding bytes
              v = v + 4 - (w & 3);
              // reads instruction
              label = w + readInt(v); v += 4;
              j = readInt(v); v += 4;
              int[] keys = new int[j];
              Label[] values = new Label[j];
              for (j = 0; j < keys.length; ++j) {
                keys[j] = readInt(v); v += 4;
                values[j] = labels[w + readInt(v)]; v += 4;
              }
              cv.visitLookupSwitchInsn(labels[label], keys, values);
              break;
            case ClassWriter.VAR_INSN:
              cv.visitVarInsn(opcode, b[v + 1] & 0xFF);
              v += 2;
              break;
            case ClassWriter.SBYTE_INSN:
              cv.visitIntInsn(opcode, b[v + 1]);
              v += 2;
              break;
            case ClassWriter.SHORT_INSN:
              cv.visitIntInsn(opcode, readShort(v + 1));
              v += 3;
              break;
            case ClassWriter.LDC_INSN:
              cv.visitLdcInsn(readConst(b[v + 1] & 0xFF, c));
              v += 2;
              break;
            case ClassWriter.LDCW_INSN:
              cv.visitLdcInsn(readConst(readUnsignedShort(v + 1), c));
              v += 3;
              break;
            case ClassWriter.FIELDORMETH_INSN:
            case ClassWriter.ITFMETH_INSN:
              int cpIndex = items[readUnsignedShort(v + 1)];
              String iowner = readClass(cpIndex, c);
              cpIndex = items[readUnsignedShort(cpIndex + 2)];
              String iname = readUTF8(cpIndex, c);
              String idesc = readUTF8(cpIndex + 2, c);
              if (opcode < Constants.INVOKEVIRTUAL) {
                cv.visitFieldInsn(opcode, iowner, iname, idesc);
              } else {
                cv.visitMethodInsn(opcode, iowner, iname, idesc);
              }
              if (opcode == Constants.INVOKEINTERFACE) {
                v += 5;
              } else {
                v += 3;
              }
              break;
            case ClassWriter.TYPE_INSN:
              cv.visitTypeInsn(opcode, readClass(v + 1, c));
              v += 3;
              break;
            case ClassWriter.IINC_INSN:
              cv.visitIincInsn(b[v + 1] & 0xFF, b[v + 2]);
              v += 3;
              break;
            // case MANA_INSN:
            default:
              cv.visitMultiANewArrayInsn(readClass(v + 1, c), b[v + 3] & 0xFF);
              v += 4;
              break;
          }
        }
        l = labels[codeEnd - codeStart];
        if (l != null) {
          cv.visitLabel(l);
        }
        // visits the try catch entries
        j = readUnsignedShort(v); v += 2;
        for ( ; j > 0; --j) {
          Label start = labels[readUnsignedShort(v)];
          Label end = labels[readUnsignedShort(v + 2)];
          Label handler = labels[readUnsignedShort(v + 4)];
          int type = readUnsignedShort(v + 6);
          if (type == 0) {
            cv.visitTryCatchBlock(start, end, handler, null);
          } else {
            cv.visitTryCatchBlock(start, end, handler, readUTF8(items[type], c));
          }
          v += 8;
        }
        // visits the local variable table
        j = readUnsignedShort(v); v += 2;
        if (!skipDebug) {
          for ( ; j > 0; --j) {
            String attrName = readUTF8(v, c);
            if (attrName.equals("LocalVariableTable")) {
              k = readUnsignedShort(v + 6);
              w = v + 8;
              for ( ; k > 0; --k) {
                label = readUnsignedShort(w);
                Label start = labels[label];
                label += readUnsignedShort(w + 2);
                Label end = labels[label];
                cv.visitLocalVariable(
                  readUTF8(w + 4, c),
                  readUTF8(w + 6, c),
                  start,
                  end,
                  readUnsignedShort(w + 8));
                w += 10;
              }
            }
            v += 6 + readInt(v + 2);
          }
        }
        // visits the other attributes
        while (cattrs != null) {
          attr = cattrs.next;
          cattrs.next = null;
          cv.visitAttribute(cattrs);
          cattrs = attr;
        }
        // visits the max stack and max locals values
        cv.visitMaxs(maxStack, maxLocals);
      }
    }
    // visits the class attributes
    Attribute last = null;
    attr = clattrs;
    while (attr != null) {
      Attribute next = attr.next;
      attr.next = last;
      last = attr;
      attr = next;
    }    
    while (last != null) {
      attr = last.next;
      last.next = null;
      classVisitor.visitAttribute(last);
      last = attr;
    }
    // visits the end of the class
    classVisitor.visitEnd();
public intgetItem(int item)
Returns the start index of the constant pool item in {@link #b b}, plus one. This method is intended for {@link Attribute} sub classes, and is normally not needed by class generators or adapters.

param
item the index a constant pool item.
return
the start index of the constant pool item in {@link #b b}, plus one.

    return items[item];
protected oracle.toplink.libraries.asm.AttributereadAttribute(oracle.toplink.libraries.asm.Attribute[] attrs, java.lang.String type, int off, int len, char[] buf, int codeOff, oracle.toplink.libraries.asm.Label[] labels)
Reads an attribute in {@link #b b}.

param
attrs prototypes of the attributes that must be parsed during the visit of the class. Any attribute whose type is not equal to the type of one the prototypes is ignored (i.e. an empty {@link Attribute} instance is returned).
param
type the type of the attribute.
param
off index of the first byte of the attribute's content in {@link #b b}. The 6 attribute header bytes, containing the type and the length of the attribute, are not taken into account here (they have already been read).
param
len the length of the attribute's content.
param
buf buffer to be used to call {@link #readUTF8 readUTF8}, {@link #readClass(int,char[]) readClass} or {@link #readConst readConst}.
param
codeOff index of the first byte of code's attribute content in {@link #b b}, or -1 if the attribute to be read is not a code attribute. The 6 attribute header bytes, containing the type and the length of the attribute, are not taken into account here.
param
labels the labels of the method's code, or null if the attribute to be read is not a code attribute.
return
the attribute that has been read, or null to skip this attribute.

    for (int i = 0; i < attrs.length; ++i) {
      if (attrs[i].type.equals(type)) {
        return attrs[i].read(this, off, len, buf, codeOff, labels);
      }
    }
    return new Attribute(type);
public intreadByte(int index)
Reads a byte value in {@link #b b}. This method is intended for {@link Attribute} sub classes, and is normally not needed by class generators or adapters.

param
index the start index of the value to be read in {@link #b b}.
return
the read value.

    return b[index] & 0xFF;
public java.lang.StringreadClass(int index, char[] buf)
Reads a class constant pool item in {@link #b b}. This method is intended for {@link Attribute} sub classes, and is normally not needed by class generators or adapters.

param
index the start index of an unsigned short value in {@link #b b}, whose value is the index of a class constant pool item.
param
buf buffer to be used to read the item. This buffer must be sufficiently large. It is not automatically resized.
return
the String corresponding to the specified class item.

    // computes the start index of the CONSTANT_Class item in b
    // and reads the CONSTANT_Utf8 item designated by
    // the first two bytes of this CONSTANT_Class item
    return readUTF8(items[readUnsignedShort(index)], buf);
private static byte[]readClass(java.io.InputStream is)
Reads the bytecode of a class.

param
is an input stream from which to read the class.
return
the bytecode read from the given input stream.
throws
IOException if a problem occurs during reading.

    if (is == null) {
      throw new IOException("Class not found");
    }
    byte[] b = new byte[is.available()];
    int len = 0;
    while (true) {
      int n = is.read(b, len, b.length - len);
      if (n == -1) {
        if (len < b.length) {
          byte[] c = new byte[len];
          System.arraycopy(b, 0, c, 0, len);
          b = c;
        }
        return b;
      } else {
        len += n;
        if (len == b.length) {
          byte[] c = new byte[b.length + 1000];
          System.arraycopy(b, 0, c, 0, len);
          b = c;
        }
      }
    }
public java.lang.ObjectreadConst(int item, char[] buf)
Reads a numeric or string constant pool item in {@link #b b}. This method is intended for {@link Attribute} sub classes, and is normally not needed by class generators or adapters.

param
item the index of a constant pool item.
param
buf buffer to be used to read the item. This buffer must be sufficiently large. It is not automatically resized.
return
the {@link java.lang.Integer Integer}, {@link java.lang.Float Float}, {@link java.lang.Long Long}, {@link java.lang.Double Double}, {@link String String} or {@link Type Type} corresponding to the given constant pool item.

    int index = items[item];
    switch (b[index - 1]) {
      case ClassWriter.INT:
        return new Integer(readInt(index));
      case ClassWriter.FLOAT:
        return new Float(Float.intBitsToFloat(readInt(index)));
      case ClassWriter.LONG:
        return new Long(readLong(index));
      case ClassWriter.DOUBLE:
        return new Double(Double.longBitsToDouble(readLong(index)));
      case ClassWriter.CLASS:
        String s = readUTF8(index, buf);
        return Type.getType(s.charAt(0) == '[" ? s : "L" + s + ";");
      //case ClassWriter.STR:
      default:
        return readUTF8(index, buf);
    }
public intreadInt(int index)
Reads a signed int value in {@link #b b}. This method is intended for {@link Attribute} sub classes, and is normally not needed by class generators or adapters.

param
index the start index of the value to be read in {@link #b b}.
return
the read value.

    byte[] b = this.b;
    return ((b[index] & 0xFF) << 24) |
           ((b[index + 1] & 0xFF) << 16) |
           ((b[index + 2] & 0xFF) << 8) |
           (b[index + 3] & 0xFF);
public longreadLong(int index)
Reads a signed long value in {@link #b b}. This method is intended for {@link Attribute} sub classes, and is normally not needed by class generators or adapters.

param
index the start index of the value to be read in {@link #b b}.
return
the read value.

    long l1 = readInt(index);
    long l0 = readInt(index + 4) & 0xFFFFFFFFL;
    return (l1 << 32) | l0;
public shortreadShort(int index)
Reads a signed short value in {@link #b b}. This method is intended for {@link Attribute} sub classes, and is normally not needed by class generators or adapters.

param
index the start index of the value to be read in {@link #b b}.
return
the read value.

    byte[] b = this.b;
    return (short)(((b[index] & 0xFF) << 8) | (b[index + 1] & 0xFF));
public java.lang.StringreadUTF8(int index, char[] buf)
Reads an UTF8 string constant pool item in {@link #b b}. This method is intended for {@link Attribute} sub classes, and is normally not needed by class generators or adapters.

param
index the start index of an unsigned short value in {@link #b b}, whose value is the index of an UTF8 constant pool item.
param
buf buffer to be used to read the item. This buffer must be sufficiently large. It is not automatically resized.
return
the String corresponding to the specified UTF8 item.

    // consults cache
    int item = readUnsignedShort(index);
    String s = strings[item];
    if (s != null) {
      return s;
    }
    // computes the start index of the CONSTANT_Utf8 item in b
    index = items[item];
    // reads the length of the string (in bytes, not characters)
    int utfLen = readUnsignedShort(index);
    index += 2;
    // parses the string bytes
    int endIndex = index + utfLen;
    byte[] b = this.b;
    int strLen = 0;
    int c, d, e;
    while (index < endIndex) {
      c = b[index++] & 0xFF;
      switch (c >> 4) {
        case 0:
        case 1:
        case 2:
        case 3:
        case 4:
        case 5:
        case 6:
        case 7:
          // 0xxxxxxx
          buf[strLen++] = (char)c;
          break;
        case 12:
        case 13:
          // 110x xxxx   10xx xxxx
          d = b[index++];
          buf[strLen++] = (char)(((c & 0x1F) << 6) | (d & 0x3F));
          break;
        default:
          // 1110 xxxx  10xx xxxx  10xx xxxx
          d = b[index++];
          e = b[index++];
          buf[strLen++] =
            (char)(((c & 0x0F) << 12) | ((d & 0x3F) << 6) | (e & 0x3F));
          break;
      }
    }
    s = new String(buf, 0, strLen);
    strings[item] = s;
    return s;
public intreadUnsignedShort(int index)
Reads an unsigned short value in {@link #b b}. This method is intended for {@link Attribute} sub classes, and is normally not needed by class generators or adapters.

param
index the start index of the value to be read in {@link #b b}.
return
the read value.

    byte[] b = this.b;
    return ((b[index] & 0xFF) << 8) | (b[index + 1] & 0xFF);