Class: JavaClass::ClassFile::JavaClassHeader

Inherits:
Object
  • Object
show all
Defined in:
lib/javaclass/classfile/java_class_header.rb

Overview

Parse and disassemble Java class files, similar to the javap command. Provides all information of a Java class file. This is just a container for all kind of specialised elements. The constuctor parses and creates all contained elements.

See

java.sun.com/docs/books/jvms/second_edition/html/ClassFile.doc.html

See

en.wikipedia.org/wiki/Class

Author

Peter Kofler

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(data) ⇒ JavaClassHeader

Create a header with the binary data from the class file.



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# File 'lib/javaclass/classfile/java_class_header.rb', line 27

def initialize(data)
  
  #  ClassFile {
  #    u4 magic; - ok
  #    u2 minor_version; - ok
  #    u2 major_version; - ok
  #    u2 constant_pool_count; - ok
  #    cp_info constant_pool[constant_pool_count-1]; - ok
  #    u2 access_flags; - ok
  #    u2 this_class; - ok
  #    u2 super_class; - ok
  # TODO implement function for fields and methods (JVM spec)
  #    u2 interfaces_count;
  #    u2 interfaces[interfaces_count];
  #    u2 fields_count;
  #    field_info fields[fields_count];
  #    u2 methods_count;
  #    method_info methods[methods_count];
  #    u2 attributes_count;
  #    attribute_info attributes[attributes_count];
  #  }
  # TODO Java 1.0 - "private protected" fields.
  
  @magic = ClassMagic.new(data)
  @version = ClassVersion.new(data)
  
  @constant_pool = ConstantPool.new(data)
  pos = 8 + @constant_pool.size
  
  @access_flags = AccessFlags.new(data, pos)
  pos += 2
  
  idx = data.u2(pos)
  pos += 2
  @this_class_idx = idx
  
  @references = References.new(@constant_pool, @this_class_idx)
  
  idx = data.u2(pos)
  pos += 2
  @super_class_idx = idx
end

Instance Attribute Details

#access_flags ⇒ Object (readonly)

Returns the value of attribute access_flags.



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# File 'lib/javaclass/classfile/java_class_header.rb', line 23

def access_flags
  @access_flags
end

#constant_pool ⇒ Object (readonly)

Returns the value of attribute constant_pool.



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# File 'lib/javaclass/classfile/java_class_header.rb', line 22

def constant_pool
  @constant_pool
end

#magic ⇒ Object (readonly)

Returns the value of attribute magic.



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# File 'lib/javaclass/classfile/java_class_header.rb', line 20

def magic
  @magic
end

#references ⇒ Object (readonly)

Returns the value of attribute references.



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# File 'lib/javaclass/classfile/java_class_header.rb', line 24

def references
  @references
end

#version ⇒ Object (readonly)

Returns the value of attribute version.



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# File 'lib/javaclass/classfile/java_class_header.rb', line 21

def version
  @version
end

Instance Method Details

#dump ⇒ Object

Return a debug output of this class that looks similar to javap output.



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# File 'lib/javaclass/classfile/java_class_header.rb', line 85

def dump
  d = []
  mod = @access_flags.public? ? 'public ' : ''
  ext = super_class ? "extends #{super_class.to_classname}" : ''
  d << "#{mod}class #{this_class.to_classname} #{ext}" 
  # d << "  SourceFile: \"#{read from LineNumberTable?}\""
  d += @version.dump 
  d += @constant_pool.dump
  d << ''
  d << '{'
  d << '}'
  d
end

#super_class ⇒ Object

Return the name of the superclass of this class or nil.



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# File 'lib/javaclass/classfile/java_class_header.rb', line 76

def super_class
  if @super_class_idx > 0
    @constant_pool[@super_class_idx].to_s.to_javaname
  else
    nil
  end
end

#this_class ⇒ Object

Return the name of this class.



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# File 'lib/javaclass/classfile/java_class_header.rb', line 71

def this_class
  @constant_pool[@this_class_idx].to_s.to_javaname
end