You can by the way use Javassist to do what I want, but it is a bit of a pain!
You can write a program that modifies Derived above so that it calls super
after initializing the field:
| package examples.vmts.initializationorder.chibaexample;
|
|
| import javassist.*;
| import javassist.bytecode.*;
|
|
| public class ModifyDerived {
| public static void main( final String[] notUsed ) throws
NotFoundException,
| BadBytecode,
|
CannotCompileException,
|
java.io.IOException {
| final CtClass ctClass = ClassPool.getDefault()
| .getAndRename(
"examples.vmts.initializationorder.chibaexample.Derived",
|
"examples.vmts.initializationorder.chibaexample.ModifiedDerived" );
| ctClass.replaceClassName(
|
"examples.vmts.initializationorder.chibaexample.ExternalTest",
|
"examples.vmts.initializationorder.chibaexample.ModifiedTest" );
|
| final ClassFile clazz = ctClass.getClassFile();
| final MethodInfo constructor = clazz.getMethod( MethodInfo.nameInit
);
| final CodeAttribute code = constructor.getCodeAttribute();
| final byte[] bytes = code.getCode();
| final CodeIterator codeIter = code.iterator();
| codeIter.skipSuperConstructor(); // move to super call, this is
what skipSuperConstructor does!
|
| if ( codeIter.hasNext() ) { // need to modify clazz, i.e. super not
last opcode
|
| final int superSize = codeIter.next(); // index of opcode after
super call
| final int rest = bytes.length - superSize - 1; // number of
bytes up to return opcode
| final byte[] superCall = new byte[ superSize ];
| System.arraycopy( bytes, 0, superCall, 0, superSize );
| System.arraycopy( bytes, superSize, bytes, 0, rest );
| System.arraycopy( superCall, 0, bytes, rest, superSize );
| }
|
| ctClass.writeFile( "C:\\Personal\\Java\\" );
| }
| }
|
The above takes class Derived and modifies it, the new class is similar except
that:
1. Its name is ModifiedDerived
2. Its field and constructor arguments are of type ModifiedTest
3. And this is the important one, it calls super after it has initialized the
field
You can test the modified class with:
| package examples.vmts.initializationorder.chibaexample;
|
|
| public class ModifiedTest {
| int field = 1;
|
| Base base() {
| return new ModifiedDerived( this );
| }
|
| public static void main( final String[] notUsed ) {
| new ModifiedTest().base();
| }
| }
|
Which gives the expected result of 1.
As I said at the start all this is a bit of a pain, any chance that the
Javassist compiler will relax the restriction that super must be first?
Keep up the good work,
Howard.
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