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JMockit is a Java toolkit for developer (unit/integration) testing. It contains mocking APIs and other tools, supporting both JUnit and TestNG. The mocking APIs allow all kinds of Java code, without testability restrictions, to be tested in isolation from selected dependencies.

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/*
 * Copyright (c) 2006-2013 Rogério Liesenfeld
 * This file is subject to the terms of the MIT license (see LICENSE.txt).
 */
package mockit.internal;

import java.lang.reflect.Type;

import org.jetbrains.annotations.*;

import mockit.external.asm4.*;
import mockit.internal.util.*;

/**
 * Allows the creation of new implementation classes for interfaces and abstract classes.
 */
public abstract class ImplementationClass
{
   @NotNull private final Type mockedType;
   private byte[] generatedBytecode;

   protected ImplementationClass(@NotNull Type mockedType) { this.mockedType = mockedType; }

   @NotNull public final Class generateNewMockImplementationClassForInterface()
   {
      Class mockedClass = Utilities.getClassType(mockedType);
      ClassReader interfaceReader = ClassFile.createClassFileReader(mockedClass);
      String mockClassName = GeneratedClasses.getNameForGeneratedClass(mockedClass);

      ClassVisitor modifier = createMethodBodyGenerator(interfaceReader, mockClassName);
      interfaceReader.accept(modifier, ClassReader.SKIP_DEBUG);

      generatedBytecode = modifier.toByteArray();

      @SuppressWarnings("unchecked")
      Class implClass = (Class) defineNewClass(mockedClass.getClassLoader(), generatedBytecode, mockClassName);

      return implClass;
   }

   @NotNull
   protected abstract ClassVisitor createMethodBodyGenerator(
      @NotNull ClassReader typeReader, @NotNull String className);

   public final byte[] getGeneratedBytecode() { return generatedBytecode; }

   @NotNull
   public static Class defineNewClass(
      @Nullable ClassLoader parentLoader, @NotNull final byte[] bytecode, @NotNull String className)
   {
      if (parentLoader == null) {
         //noinspection AssignmentToMethodParameter
         parentLoader = ImplementationClass.class.getClassLoader();
      }

      return new ClassLoader(parentLoader) {
         @Override
         protected Class findClass(String name)
         {
            return defineClass(name, bytecode, 0, bytecode.length);
         }
      }.findClass(className);
   }
}