Package javassist.bytecode

Class ClassFile

java.lang.Object
javassist.bytecode.ClassFile
public final class ClassFile extends Object
ClassFile represents a Java .class file, which consists of a constant pool, methods, fields, and attributes.

For example,

 ClassFile cf = new ClassFile(false, "test.Foo", null);
 cf.setInterfaces(new String[] { "java.lang.Cloneable" });

 FieldInfo f = new FieldInfo(cf.getConstPool(), "width", "I");
 f.setAccessFlags(AccessFlag.PUBLIC);
 cf.addField(f);

 cf.write(new DataOutputStream(new FileOutputStream("Foo.class")));

This code generates a class file Foo.class for the following class:

 package test;
 class Foo implements Cloneable {
     public int width;
 }
See Also:

  • Field Details

    • JAVA_1

      public static final int JAVA_1
      The major version number of class files for JDK 1.1.
      See Also:

    • JAVA_2

      public static final int JAVA_2
      The major version number of class files for JDK 1.2.
      See Also:

    • JAVA_3

      public static final int JAVA_3
      The major version number of class files for JDK 1.3.
      See Also:

    • JAVA_4

      public static final int JAVA_4
      The major version number of class files for JDK 1.4.
      See Also:

    • JAVA_5

      public static final int JAVA_5
      The major version number of class files for JDK 1.5.
      See Also:

    • JAVA_6

      public static final int JAVA_6
      The major version number of class files for JDK 1.6.
      See Also:

    • JAVA_7

      public static final int JAVA_7
      The major version number of class files for JDK 1.7.
      See Also:

    • JAVA_8

      public static final int JAVA_8
      The major version number of class files for JDK 1.8.
      See Also:

    • JAVA_9

      public static final int JAVA_9
      The major version number of class files for JDK 1.9.
      See Also:

    • JAVA_10

      public static final int JAVA_10
      The major version number of class files for JDK 10.
      See Also:

    • JAVA_11

      public static final int JAVA_11
      The major version number of class files for JDK 11.
      See Also:

    • MAJOR_VERSION

      public static final int MAJOR_VERSION
      The major version number of class files created from scratch. The default value is 47 (JDK 1.3). It is 49 (JDK 1.5) if the JVM supports java.lang.StringBuilder. It is 50 (JDK 1.6) if the JVM supports java.util.zip.DeflaterInputStream. It is 51 (JDK 1.7) if the JVM supports java.lang.invoke.CallSite. It is 52 (JDK 1.8) if the JVM supports java.util.function.Function. It is 53 (JDK 1.9) if the JVM supports java.lang.reflect.Module. It is 54 (JDK 10) if the JVM supports java.util.List.copyOf(Collection). It is 55 (JDK 11) if the JVM supports java.util.Optional.isEmpty().

  • Constructor Details

    • ClassFile

      public ClassFile(DataInputStream in) throws IOException
      Constructs a class file from a byte stream.
      Throws:
      IOException

    • ClassFile

      public ClassFile(boolean isInterface, String classname, String superclass)
      Constructs a class file including no members.
      Parameters:
      isInterface - true if this is an interface. false if this is a class.
      classname - a fully-qualified class name
      superclass - a fully-qualified super class name or null.

  • Method Details

    • compact

      public void compact()
      Eliminates dead constant pool items. If a method or a field is removed, the constant pool items used by that method/field become dead items. This method recreates a constant pool.

    • prune

      public void prune()
      Discards all attributes, associated with both the class file and the members such as a code attribute and exceptions attribute. The unused constant pool entries are also discarded (a new packed constant pool is constructed).

    • getConstPool

      public ConstPool getConstPool()
      Returns a constant pool table.

    • isInterface

      public boolean isInterface()
      Returns true if this is an interface.

    • isFinal

      public boolean isFinal()
      Returns true if this is a final class or interface.

    • isAbstract

      public boolean isAbstract()
      Returns true if this is an abstract class or an interface.

    • getAccessFlags

      public int getAccessFlags()
      Returns access flags.
      See Also:

    • setAccessFlags

      public void setAccessFlags(int acc)
      Changes access flags.
      See Also:

    • getInnerAccessFlags

      public int getInnerAccessFlags()
      Returns access and property flags of this nested class. This method returns -1 if the class is not a nested class.

      The returned value is obtained from inner_class_access_flags of the entry representing this nested class itself in InnerClasses_attribute.

    • getName

      public String getName()
      Returns the class name.

    • setName

      public void setName(String name)
      Sets the class name. This method substitutes the new name for all occurrences of the old class name in the class file.

    • getSuperclass

      public String getSuperclass()
      Returns the super class name.

    • getSuperclassId

      public int getSuperclassId()
      Returns the index of the constant pool entry representing the super class.

    • setSuperclass

      public void setSuperclass(String superclass) throws CannotCompileException
      Sets the super class.

      The new super class should inherit from the old super class. This method modifies constructors so that they call constructors declared in the new super class.

      Throws:
      CannotCompileException

    • renameClass

      public final void renameClass(String oldname, String newname)
      Replaces all occurrences of a class name in the class file.

      If class X is substituted for class Y in the class file, X and Y must have the same signature. If Y provides a method m(), X must provide it even if X inherits m() from the super class. If this fact is not guaranteed, the bytecode verifier may cause an error.

      Parameters:
      oldname - the replaced class name
      newname - the substituted class name

    • renameClass

      public final void renameClass(Map<String,String> classnames)
      Replaces all occurrences of several class names in the class file.
      Parameters:
      classnames - specifies which class name is replaced with which new name. Class names must be described with the JVM-internal representation like java/lang/Object.
      See Also:

    • getRefClasses

      public final void getRefClasses(Map<String,String> classnames)
      Internal-use only. CtClass.getRefClasses() calls this method.

    • getInterfaces

      public String[] getInterfaces()
      Returns the names of the interfaces implemented by the class. The returned array is read only.

    • setInterfaces

      public void setInterfaces(String[] nameList)
      Sets the interfaces.
      Parameters:
      nameList - the names of the interfaces.

    • addInterface

      public void addInterface(String name)
      Appends an interface to the interfaces implemented by the class.

    • getFields

      public List<FieldInfo> getFields()
      Returns all the fields declared in the class.
      Returns:
      a list of FieldInfo.
      See Also:

    • addField

      public void addField(FieldInfo finfo) throws DuplicateMemberException
      Appends a field to the class.
      Throws:
      DuplicateMemberException - when the field is already included.

    • addField2

      public final void addField2(FieldInfo finfo)
      Just appends a field to the class. It does not check field duplication. Use this method only when minimizing performance overheads is seriously required.
      Since:
      3.13

    • getMethods

      public List<MethodInfo> getMethods()
      Returns all the methods declared in the class.
      Returns:
      a list of MethodInfo.
      See Also:

    • getMethod

      public MethodInfo getMethod(String name)
      Returns the method with the specified name. If there are multiple methods with that name, this method returns one of them.
      Returns:
      null if no such method is found.

    • getStaticInitializer

      public MethodInfo getStaticInitializer()
      Returns a static initializer (class initializer), or null if it does not exist.

    • addMethod

      public void addMethod(MethodInfo minfo) throws DuplicateMemberException
      Appends a method to the class. If there is a bridge method with the same name and signature, then the bridge method is removed before a new method is added.
      Throws:
      DuplicateMemberException - when the method is already included.

    • addMethod2

      public final void addMethod2(MethodInfo minfo)
      Just appends a method to the class. It does not check method duplication or remove a bridge method. Use this method only when minimizing performance overheads is seriously required.
      Since:
      3.13

    • getAttributes

      public List<AttributeInfo> getAttributes()
      Returns all the attributes. The returned List object is shared with this object. If you add a new attribute to the list, the attribute is also added to the classs file represented by this object. If you remove an attribute from the list, it is also removed from the class file.
      Returns:
      a list of AttributeInfo objects.
      See Also:

    • getAttribute

      public AttributeInfo getAttribute(String name)
      Returns the attribute with the specified name. If there are multiple attributes with that name, this method returns either of them. It returns null if the specified attributed is not found.

      An attribute name can be obtained by, for example, AnnotationsAttribute.visibleTag or AnnotationsAttribute.invisibleTag.

      Parameters:
      name - attribute name
      See Also:

    • removeAttribute

      public AttributeInfo removeAttribute(String name)
      Removes an attribute with the specified name.
      Parameters:
      name - attribute name.
      Returns:
      the removed attribute or null.
      Since:
      3.21

    • addAttribute

      public void addAttribute(AttributeInfo info)
      Appends an attribute. If there is already an attribute with the same name, the new one substitutes for it.
      See Also:

    • getSourceFile

      public String getSourceFile()
      Returns the source file containing this class.
      Returns:
      null if this information is not available.

    • write

      public void write(DataOutputStream out) throws IOException
      Writes a class file represented by this object into an output stream.
      Throws:
      IOException

    • getMajorVersion

      public int getMajorVersion()
      Get the Major version.
      Returns:
      the major version

    • setMajorVersion

      public void setMajorVersion(int major)
      Set the major version.
      Parameters:
      major - the major version

    • getMinorVersion

      public int getMinorVersion()
      Get the minor version.
      Returns:
      the minor version

    • setMinorVersion

      public void setMinorVersion(int minor)
      Set the minor version.
      Parameters:
      minor - the minor version

    • setVersionToJava5

      public void setVersionToJava5()
      Sets the major and minor version to Java 5. If the major version is older than 49, Java 5 extensions such as annotations are ignored by the JVM.