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JMockit is a Java toolkit for automated developer testing. It contains mocking/faking APIs and a code coverage tool, 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 JMockit developers
 * This file is subject to the terms of the MIT license (see LICENSE.txt).
 */
package mockit.coverage.paths;

import java.util.*;
import javax.annotation.*;

import mockit.asm.controlFlow.*;
import mockit.asm.jvmConstants.*;
import mockit.coverage.paths.Node.*;

public final class NodeBuilder
{
   public int firstLine;
   @Nonnull final List nodes = new ArrayList<>();

   @Nullable private Entry entryNode;
   @Nullable private SimpleFork currentSimpleFork;
   @Nullable private BasicBlock currentBasicBlock;
   @Nullable private Join currentJoin;
   @Nonnull private final Map> jumpTargetToForks = new LinkedHashMap<>();
   @Nonnull private final Map> gotoTargetToSuccessors = new LinkedHashMap<>();

   private int potentiallyTrivialJump;

   public void handleEntry(@Nonnegative int line) {
      firstLine = line;
      entryNode = new Entry(line);
      addNewNode(entryNode);
   }

   private int addNewNode(@Nonnull Node newNode) {
      int newNodeIndex = nodes.size();

      if (newNodeIndex == 0 && !(newNode instanceof Entry)) {
         return -1;
      }

      nodes.add(newNode);

      if (newNodeIndex > 0) {
         Node precedingNode = nodes.get(newNodeIndex - 1);

         if (precedingNode.line == newNode.line) {
            newNode.setSegmentAccordingToPrecedingNode(precedingNode);
         }
      }

      return newNodeIndex;
   }

   public boolean hasNodes() { return !nodes.isEmpty(); }

   public int handleRegularInstruction(@Nonnegative int line, int opcode) {
      if (currentSimpleFork == null && currentJoin == null) {
         potentiallyTrivialJump = 0;
         return -1;
      }

      assert currentBasicBlock == null;

      BasicBlock newNode = new BasicBlock(line);
      connectNodes(newNode, opcode);

      return addNewNode(newNode);
   }

   public int handleJump(@Nonnull Label targetBlock, @Nonnegative int line, boolean conditional) {
      if (conditional) {
         SimpleFork newFork = new SimpleFork(line);
         connectNodes(targetBlock, newFork);
         currentSimpleFork = newFork;
         potentiallyTrivialJump = 1;
         return addNewNode(newFork);
      }
      else if (currentBasicBlock == null && currentJoin == null) {
         Goto newGoto = new Goto(line);
         connectNodes(newGoto);
         setUpMappingFromGotoTargetToCurrentGotoSuccessor(targetBlock, newGoto);
         return addNewNode(newGoto);
      }
      else {
         setUpMappingFromGotoTargetToCurrentGotoSuccessor(targetBlock, null);
         return -1;
      }
   }

   public int handleJumpTarget(@Nonnull Label basicBlock, @Nonnegative int line) {
      // Ignore for visitLabel calls preceding visitLineNumber:
      if (isNewLineTarget(basicBlock)) {
         return -1;
      }

      Join newNode = new Join(line);
      connectNodes(basicBlock, newNode);

      return addNewNode(newNode);
   }

   private boolean isNewLineTarget(@Nonnull Label basicBlock) {
      return !jumpTargetToForks.containsKey(basicBlock) && !gotoTargetToSuccessors.containsKey(basicBlock);
   }

   private void connectNodes(@Nonnull BasicBlock newBasicBlock, int opcode) {
      if (currentSimpleFork != null) {
         currentSimpleFork.nextConsecutiveNode = newBasicBlock;
         currentSimpleFork = null;

         if (potentiallyTrivialJump == 1) {
            potentiallyTrivialJump = opcode == Opcodes.ICONST_1 ? 2 : 0;
         }
      }
      else {
         assert currentJoin != null;

         if (potentiallyTrivialJump == 3) {
            if (opcode == Opcodes.ICONST_0) {
               currentJoin.fromTrivialFork = true;
            }

            potentiallyTrivialJump = 0;
         }

         currentJoin.nextNode = newBasicBlock;
         currentJoin = null;
      }

      currentBasicBlock = newBasicBlock;
   }

   private void connectNodes(@Nonnull Label targetBlock, @Nonnull Fork newFork) {
      assert entryNode != null;

      if (entryNode.nextNode == null) {
         entryNode.nextNode = newFork;
      }

      setUpMappingFromConditionalTargetToFork(targetBlock, newFork);
      connectNodes(newFork);
   }

   private void setUpMappingFromConditionalTargetToFork(@Nonnull Label targetBlock, @Nonnull Fork newFork) {
      List forksWithSameTarget = jumpTargetToForks.get(targetBlock);

      if (forksWithSameTarget == null) {
         forksWithSameTarget = new LinkedList<>();
         jumpTargetToForks.put(targetBlock, forksWithSameTarget);
      }

      forksWithSameTarget.add(newFork);
   }

   private void setUpMappingFromGotoTargetToCurrentGotoSuccessor(@Nonnull Label targetBlock, @Nullable Goto gotoNode) {
      List successors = gotoTargetToSuccessors.get(targetBlock);

      if (successors == null) {
         successors = new LinkedList<>();
         gotoTargetToSuccessors.put(targetBlock, successors);
      }

      // TODO: they both can be non-null here; what to do?
      if (currentBasicBlock != null) {
         assert currentJoin == null : "Ambiguous situation for " + targetBlock;
         successors.add(currentBasicBlock);
         currentBasicBlock = null;

         if (potentiallyTrivialJump == 2) {
            potentiallyTrivialJump = 3;
         }
      }
      else if (currentJoin != null) {
         successors.add(currentJoin);
         currentJoin = null;
      }
      else {
         successors.add(gotoNode);
      }
   }

   private void connectNodes(@Nonnull Label basicBlock, @Nonnull Join newJoin) {
      connectNodes(newJoin);
      connectSourceForksToTargetedJoin(basicBlock, newJoin);
      connectGotoSuccessorsToNewJoin(basicBlock, newJoin);
      currentJoin = newJoin;
   }

   public int handleExit(@Nonnegative int exitLine) {
      Exit newNode = new Exit(exitLine);
      connectNodes(newNode);

      return addNewNode(newNode);
   }

   private void connectNodes(@Nonnull ConditionalSuccessor newNode) {
      if (currentSimpleFork != null) {
         currentSimpleFork.nextConsecutiveNode = newNode;
         currentSimpleFork = null;
         assert currentJoin == null;
         assert currentBasicBlock == null;
      }

      if (currentJoin != null) {
         currentJoin.nextNode = newNode;
         currentJoin = null;
         assert currentBasicBlock == null;
      }

      if (currentBasicBlock != null) {
         currentBasicBlock.nextConsecutiveNode = newNode;
         currentBasicBlock = null;
      }
   }

   private void connectSourceForksToTargetedJoin(@Nonnull Label targetBlock, @Nonnull Join newJoin) {
      List forks = jumpTargetToForks.get(targetBlock);

      if (forks != null) {
         for (Fork fork : forks) {
            fork.addNextNode(newJoin);
         }

         jumpTargetToForks.remove(targetBlock);
      }
   }

   private void connectGotoSuccessorsToNewJoin(@Nonnull Label targetBlock, @Nonnull Join newJoin) {
      List successors = gotoTargetToSuccessors.get(targetBlock);

      if (successors != null) {
         for (GotoSuccessor successorToGoto : successors) {
            successorToGoto.setNextNodeAfterGoto(newJoin);
         }

         gotoTargetToSuccessors.remove(targetBlock);
      }
   }

   public int handleForwardJumpsToNewTargets(@Nonnull Label defaultBlock, @Nonnull Label[] caseBlocks, @Nonnegative int line) {
      Fork newJoin = new MultiFork(line);

      for (Label targetBlock : caseBlocks) {
         if (targetBlock != defaultBlock) {
            connectNodes(targetBlock, newJoin);
         }
      }

      connectNodes(defaultBlock, newJoin);

      return addNewNode(newJoin);
   }
}