CheckClassAdapter (ASM 5.0.3 Documentation)

java.lang.Object
- org.objectweb.asm.ClassVisitor
- - org.objectweb.asm.util.CheckClassAdapter

```
public class CheckClassAdapter
extends ClassVisitor
```
A ClassVisitor that checks that its methods are properly used. More precisely this class adapter checks each method call individually, based only on its arguments, but does not check the sequence of method calls. For example, the invalid sequence visitField(ACC_PUBLIC, "i", "I", null) visitField(ACC_PUBLIC, "i", "D", null) will not be detected by this class adapter.
CheckClassAdapter can be also used to verify bytecode transformations in order to make sure transformed bytecode is sane. For example:
```
   InputStream is = ...; // get bytes for the source class
   ClassReader cr = new ClassReader(is);
   ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS);
   ClassVisitor cv = new MyClassAdapter(new CheckClassAdapter(cw));
   cr.accept(cv, 0);
 
   StringWriter sw = new StringWriter();
   PrintWriter pw = new PrintWriter(sw);
   CheckClassAdapter.verify(new ClassReader(cw.toByteArray()), false, pw);
   assertTrue(sw.toString(), sw.toString().length()==0);
 
```
Above code runs transformed bytecode trough the CheckClassAdapter. It won't be exactly the same verification as JVM does, but it run data flow analysis for the code of each method and checks that expectations are met for each method instruction.
If method bytecode has errors, assertion text will show the erroneous instruction number and dump of the failed method with information about locals and stack slot for each instruction. For example (format is - insnNumber locals : stack):
```
 org.objectweb.asm.tree.analysis.AnalyzerException: Error at instruction 71: Expected I, but found .
   at org.objectweb.asm.tree.analysis.Analyzer.analyze(Analyzer.java:289)
   at org.objectweb.asm.util.CheckClassAdapter.verify(CheckClassAdapter.java:135)
 ...
 remove()V
 00000 LinkedBlockingQueue$Itr . . . . . . . .  :
   ICONST_0
 00001 LinkedBlockingQueue$Itr . . . . . . . .  : I
   ISTORE 2
 00001 LinkedBlockingQueue$Itr . I . . . . . .  :
 ...
 
 00071 LinkedBlockingQueue$Itr . I . . . . . .  :
   ILOAD 1
 00072 ?
   INVOKESPECIAL java/lang/Integer.<init> (I)V
 ...
 
```
In the above output you can see that variable 1 loaded by ILOAD 1 instruction at position 00071 is not initialized. You can also see that at the beginning of the method (code inserted by the transformation) variable 2 is initialized.
Note that when used like that, CheckClassAdapter.verify() can trigger additional class loading, because it is using SimpleVerifier.
Author:

Eric Bruneton

Field Summary
- Fields inherited from class org.objectweb.asm.ClassVisitor
  api, cv

Constructor Summary

Constructors
Modifier	Constructor and Description
	`CheckClassAdapter(ClassVisitor cv)` Constructs a new `CheckClassAdapter`.
	`CheckClassAdapter(ClassVisitor cv, boolean checkDataFlow)` Constructs a new `CheckClassAdapter`.
`protected`	`CheckClassAdapter(int api, ClassVisitor cv, boolean checkDataFlow)` Constructs a new `CheckClassAdapter`.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`static void`	`checkClassSignature(String signature)` Checks a class signature.
`static void`	`checkFieldSignature(String signature)` Checks a field signature.
`static void`	`checkMethodSignature(String signature)` Checks a method signature.
`static void`	`main(String[] args)` Checks a given class.
`static void`	`verify(ClassReader cr, boolean dump, PrintWriter pw)` Checks a given class
`static void`	`verify(ClassReader cr, ClassLoader loader, boolean dump, PrintWriter pw)` Checks a given class.
`void`	`visit(int version, int access, String name, String signature, String superName, String[] interfaces)` Visits the header of the class.
`AnnotationVisitor`	`visitAnnotation(String desc, boolean visible)` Visits an annotation of the class.
`void`	`visitAttribute(Attribute attr)` Visits a non standard attribute of the class.
`void`	`visitEnd()` Visits the end of the class.
`FieldVisitor`	`visitField(int access, String name, String desc, String signature, Object value)` Visits a field of the class.
`void`	`visitInnerClass(String name, String outerName, String innerName, int access)` Visits information about an inner class.
`MethodVisitor`	`visitMethod(int access, String name, String desc, String signature, String[] exceptions)` Visits a method of the class.
`void`	`visitOuterClass(String owner, String name, String desc)` Visits the enclosing class of the class.
`void`	`visitSource(String file, String debug)` Visits the source of the class.
`AnnotationVisitor`	`visitTypeAnnotation(int typeRef, TypePath typePath, String desc, boolean visible)` Visits an annotation on a type in the class signature.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - CheckClassAdapter
```
public CheckClassAdapter(ClassVisitor cv)
```
    Constructs a new CheckClassAdapter. Subclasses must not use this constructor. Instead, they must use the CheckClassAdapter(int, ClassVisitor, boolean) version.
    
    Parameters:
    
    cv - the class visitor to which this adapter must delegate calls.
  - CheckClassAdapter
```
public CheckClassAdapter(ClassVisitor cv,
                         boolean checkDataFlow)
```
    Constructs a new CheckClassAdapter. Subclasses must not use this constructor. Instead, they must use the CheckClassAdapter(int, ClassVisitor, boolean) version.
    
    Parameters:
    
    cv - the class visitor to which this adapter must delegate calls.
    
    checkDataFlow - true to perform basic data flow checks, or false to not perform any data flow check (see CheckMethodAdapter). This option requires valid maxLocals and maxStack values.
    
    Throws:
    
    IllegalStateException - If a subclass calls this constructor.
  - CheckClassAdapter
```
protected CheckClassAdapter(int api,
                            ClassVisitor cv,
                            boolean checkDataFlow)
```
    Constructs a new CheckClassAdapter.
    
    Parameters:
    
    api - the ASM API version implemented by this visitor. Must be one of Opcodes.ASM4 or Opcodes.ASM5.
    
    cv - the class visitor to which this adapter must delegate calls.
    
    checkDataFlow - true to perform basic data flow checks, or false to not perform any data flow check (see CheckMethodAdapter). This option requires valid maxLocals and maxStack values.
- Method Detail
  - main
```
public static void main(String[] args)
                 throws Exception
```
    Checks a given class.
    Usage: CheckClassAdapter <binary class name or class file name>
    
    Parameters:
    
    args - the command line arguments.
    
    Throws:
    
    Exception - if the class cannot be found, or if an IO exception occurs.
  - verify
```
public static void verify(ClassReader cr,
                          ClassLoader loader,
                          boolean dump,
                          PrintWriter pw)
```
    Checks a given class.
    
    Parameters:
    
    cr - a ClassReader that contains bytecode for the analysis.
    
    loader - a ClassLoader which will be used to load referenced classes. This is useful if you are verifiying multiple interdependent classes.
    
    dump - true if bytecode should be printed out not only when errors are found.
    
    pw - write where results going to be printed
  - verify
```
public static void verify(ClassReader cr,
                          boolean dump,
                          PrintWriter pw)
```
    Checks a given class
    
    Parameters:
    
    cr - a ClassReader that contains bytecode for the analysis.
    
    dump - true if bytecode should be printed out not only when errors are found.
    
    pw - write where results going to be printed
  - visit
```
public void visit(int version,
                  int access,
                  String name,
                  String signature,
                  String superName,
                  String[] interfaces)
```
    Description copied from class: ClassVisitor
    
    Visits the header of the class.
    
    Overrides:
    
    visit in class ClassVisitor
    
    Parameters:
    
    version - the class version.
    
    access - the class's access flags (see Opcodes). This parameter also indicates if the class is deprecated.
    
    name - the internal name of the class (see getInternalName).
    
    signature - the signature of this class. May be null if the class is not a generic one, and does not extend or implement generic classes or interfaces.
    
    superName - the internal of name of the super class (see getInternalName). For interfaces, the super class is Object. May be null, but only for the Object class.
    
    interfaces - the internal names of the class's interfaces (see getInternalName). May be null.
  - visitSource
```
public void visitSource(String file,
                        String debug)
```
    Description copied from class: ClassVisitor
    
    Visits the source of the class.
    
    Overrides:
    
    visitSource in class ClassVisitor
    
    Parameters:
    
    file - the name of the source file from which the class was compiled. May be null.
    
    debug - additional debug information to compute the correspondance between source and compiled elements of the class. May be null.
  - visitOuterClass
```
public void visitOuterClass(String owner,
                            String name,
                            String desc)
```
    Description copied from class: ClassVisitor
    
    Visits the enclosing class of the class. This method must be called only if the class has an enclosing class.
    
    Overrides:
    
    visitOuterClass in class ClassVisitor
    
    Parameters:
    
    owner - internal name of the enclosing class of the class.
    
    name - the name of the method that contains the class, or null if the class is not enclosed in a method of its enclosing class.
    
    desc - the descriptor of the method that contains the class, or null if the class is not enclosed in a method of its enclosing class.
  - visitInnerClass
```
public void visitInnerClass(String name,
                            String outerName,
                            String innerName,
                            int access)
```
    Description copied from class: ClassVisitor
    
    Visits information about an inner class. This inner class is not necessarily a member of the class being visited.
    
    Overrides:
    
    visitInnerClass in class ClassVisitor
    
    Parameters:
    
    name - the internal name of an inner class (see getInternalName).
    
    outerName - the internal name of the class to which the inner class belongs (see getInternalName). May be null for not member classes.
    
    innerName - the (simple) name of the inner class inside its enclosing class. May be null for anonymous inner classes.
    
    access - the access flags of the inner class as originally declared in the enclosing class.
  - visitField
```
public FieldVisitor visitField(int access,
                               String name,
                               String desc,
                               String signature,
                               Object value)
```
    Description copied from class: ClassVisitor
    
    Visits a field of the class.
    
    Overrides:
    
    visitField in class ClassVisitor
    
    Parameters:
    
    access - the field's access flags (see Opcodes). This parameter also indicates if the field is synthetic and/or deprecated.
    
    name - the field's name.
    
    desc - the field's descriptor (see Type).
    
    signature - the field's signature. May be null if the field's type does not use generic types.
    
    value - the field's initial value. This parameter, which may be null if the field does not have an initial value, must be an Integer, a Float, a Long, a Double or a String (for int, float, long or String fields respectively). This parameter is only used for static fields. Its value is ignored for non static fields, which must be initialized through bytecode instructions in constructors or methods.
    
    Returns:
    
    a visitor to visit field annotations and attributes, or null if this class visitor is not interested in visiting these annotations and attributes.
  - visitMethod
```
public MethodVisitor visitMethod(int access,
                                 String name,
                                 String desc,
                                 String signature,
                                 String[] exceptions)
```
    Description copied from class: ClassVisitor
    
    Visits a method of the class. This method must return a new MethodVisitor instance (or null) each time it is called, i.e., it should not return a previously returned visitor.
    
    Overrides:
    
    visitMethod in class ClassVisitor
    
    Parameters:
    
    access - the method's access flags (see Opcodes). This parameter also indicates if the method is synthetic and/or deprecated.
    
    name - the method's name.
    
    desc - the method's descriptor (see Type).
    
    signature - the method's signature. May be null if the method parameters, return type and exceptions do not use generic types.
    
    exceptions - the internal names of the method's exception classes (see getInternalName). May be null.
    
    Returns:
    
    an object to visit the byte code of the method, or null if this class visitor is not interested in visiting the code of this method.
  - visitAnnotation
```
public AnnotationVisitor visitAnnotation(String desc,
                                         boolean visible)
```
    Description copied from class: ClassVisitor
    
    Visits an annotation of the class.
    
    Overrides:
    
    visitAnnotation in class ClassVisitor
    
    Parameters:
    
    desc - the class descriptor of the annotation class.
    
    visible - true if the annotation is visible at runtime.
    
    Returns:
    
    a visitor to visit the annotation values, or null if this visitor is not interested in visiting this annotation.
  - visitTypeAnnotation
```
public AnnotationVisitor visitTypeAnnotation(int typeRef,
                                             TypePath typePath,
                                             String desc,
                                             boolean visible)
```
    Description copied from class: ClassVisitor
    
    Visits an annotation on a type in the class signature.
    
    Overrides:
    
    visitTypeAnnotation in class ClassVisitor
    
    Parameters:
    
    typeRef - a reference to the annotated type. The sort of this type reference must be CLASS_TYPE_PARAMETER, CLASS_TYPE_PARAMETER_BOUND or CLASS_EXTENDS. See TypeReference.
    
    typePath - the path to the annotated type argument, wildcard bound, array element type, or static inner type within 'typeRef'. May be null if the annotation targets 'typeRef' as a whole.
    
    desc - the class descriptor of the annotation class.
    
    visible - true if the annotation is visible at runtime.
    
    Returns:
    
    a visitor to visit the annotation values, or null if this visitor is not interested in visiting this annotation.
  - visitAttribute
```
public void visitAttribute(Attribute attr)
```
    Description copied from class: ClassVisitor
    
    Visits a non standard attribute of the class.
    
    Overrides:
    
    visitAttribute in class ClassVisitor
    
    Parameters:
    
    attr - an attribute.
  - visitEnd
```
public void visitEnd()
```
    Description copied from class: ClassVisitor
    
    Visits the end of the class. This method, which is the last one to be called, is used to inform the visitor that all the fields and methods of the class have been visited.
    
    Overrides:
    
    visitEnd in class ClassVisitor
  - checkClassSignature
```
public static void checkClassSignature(String signature)
```
    Checks a class signature.
    
    Parameters:
    
    signature - a string containing the signature that must be checked.
  - checkMethodSignature
```
public static void checkMethodSignature(String signature)
```
    Checks a method signature.
    
    Parameters:
    
    signature - a string containing the signature that must be checked.
  - checkFieldSignature
```
public static void checkFieldSignature(String signature)
```
    Checks a field signature.
    
    Parameters:
    
    signature - a string containing the signature that must be checked.

Class CheckClassAdapter

Field Summary

Fields inherited from class org.objectweb.asm.ClassVisitor

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

CheckClassAdapter

CheckClassAdapter

CheckClassAdapter

Method Detail

main

verify

verify

visit

visitSource

visitOuterClass

visitInnerClass

visitField

visitMethod

visitAnnotation

visitTypeAnnotation

visitAttribute

visitEnd

checkClassSignature

checkMethodSignature

checkFieldSignature