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  * JBoss, Home of Professional Open Source
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package org.jboss.weld.util.bytecode;
import static org.jboss.classfilewriter.util.DescriptorUtils.methodDescriptor;
Utility class for working with constructors in the low level javassist API

Stuart Douglas
public class ConstructorUtils {
    private ConstructorUtils() {

adds a constructor that calls super()
    public static void addDefaultConstructor(ClassFile fileList<DeferredBytecodeinitialValueBytecodefinal boolean useUnsafeInstantiators) {
        addConstructor(.new String[0], new String[0], fileinitialValueBytecodeuseUnsafeInstantiators);

Adds a constructor that delegates to a super constructor with the same descriptor. The bytecode in initialValueBytecode will be executed at the start of the constructor and can be used to initialize fields to a default value. As the object is not properly constructed at this point this bytecode may not reference this (i.e. the variable at location 0)

returnType the constructor descriptor
exceptions any exceptions that are thrown
file the classfile to add the constructor to
initialValueBytecode bytecode that can be used to set initial values
    public static void addConstructor(String returnTypeString[] paramsString[] exceptionsClassFile fileList<DeferredBytecodeinitialValueBytecodefinal boolean useUnsafeInstantiators) {
        try {
            final String initMethodName = "<init>";
            final ClassMethod ctor = file.addMethod(.initMethodNamereturnTypeparams);
            final CodeAttribute b = ctor.getCodeAttribute();
            for(final DeferredBytecode iv : initialValueBytecode) {
            // we need to generate a constructor with a single invokespecial call
            // to the super constructor
            // to do this we need to push all the arguments on the stack first
            // local variables is the number of parameters +1 for this
            // if some of the parameters are wide this may go up.
            // now we have the parameters on the stack
            b.invokespecial(file.getSuperclass(), initMethodNamemethodDescriptor(paramsreturnType));
            if(!useUnsafeInstantiators) {
                // now set constructed to true
        }  catch (DuplicateMemberException e) {
            throw new RuntimeException(e);
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