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Code is Data: Analyzing Code

Code analysis has many motivations. In this example we will see how we can resolve bugs by analyzing code with automated queries, instead of reading code manually. In this example we will try and identify methods and classes that are not used at all.

Parsing=Turning Code into Data

In this example we use Rascal's JDT library, which wraps Eclipse's Java Development Toolkit compiler for Java and makes its information available as Rascal data types. This intermediate model is called M3, and its definition is split acros a generic language independent module called Core and a Java specific part called Core.

rascal>import lang::java::m3::Core;
ok
rascal>import lang::java::m3::AST;
ok

"Snakes and Ladders" is an example Java project of which we have stored the source code in |tmp:///snakes-and-ladders/src|

rascal>|tmp:///snakes-and-ladders/src/snakes/|.ls
list[loc]: [
|tmp:///snakes-and-ladders/src/snakes/Die.java|,
|tmp:///snakes-and-ladders/src/snakes/SimpleGameTest.java|,
|tmp:///snakes-and-ladders/src/snakes/LastSquare.java|,
|tmp:///snakes-and-ladders/src/snakes/Snake.java|,
|tmp:///snakes-and-ladders/src/snakes/Ladder.java|,
|tmp:///snakes-and-ladders/src/snakes/FirstSquare.java|,
|tmp:///snakes-and-ladders/src/snakes/DieTest.java|,
|tmp:///snakes-and-ladders/src/snakes/Player.java|,
|tmp:///snakes-and-ladders/src/snakes/Game.java|,
|tmp:///snakes-and-ladders/src/snakes/ISquare.java|,
|tmp:///snakes-and-ladders/src/snakes/Square.java|
]

Now we can extract an overview model:

rascal>myModel = createM3FromDirectory(|tmp:///snakes-and-ladders/src|);
M3: m3(
|tmp:///snakes-and-ladders/src|,
annotations={
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/Snake/squareLabel()|,|java+interface:///java/lang/Override|>,
<|java+method:///snakes/Ladder/landHereOrGoHome()|,|java+interface:///java/lang/Override|>,
<|java+method:///snakes/SimpleGameTest/newGame()|,|java+class:///Test|>,
<|java+method:///snakes/SimpleGameTest/move8jillWins(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/FirstSquare/isFirstSquare()|,|java+interface:///java/lang/Override|>,
<|java+method:///snakes/Ladder/squareLabel()|,|java+interface:///java/lang/Override|>,
<|java+method:///snakes/FirstSquare/isOccupied()|,|java+interface:///java/lang/Override|>,
<|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/DieTest/testInRange()|,|java+class:///Test|>,
<|java+method:///snakes/DieTest/testMinReached()|,|java+class:///Test|>,
<|java+class:///snakes/SimpleGameTest|,|java+class:///RunWith|>,
<|java+method:///snakes/SimpleGameTest/move2jackBackwards(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/DieTest/testMaxReached()|,|java+class:///Test|>,
<|java+method:///snakes/SimpleGameTest/move5jackLadder(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/SimpleGameTest/move6jill(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/FirstSquare/enter(snakes.Player)|,|java+interface:///java/lang/Override|>,
<|java+method:///snakes/LastSquare/isLastSquare()|,|java+interface:///java/lang/Override|>,
<|java+method:///snakes/FirstSquare/leave(snakes.Player)|,|java+interface:///java/lang/Override|>,
<|java+method:///snakes/SimpleGameTest/move3jackMeetsJill(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/SimpleGameTest/move2jillLadder(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/SimpleGameTest/move7jackBouncesBackToJill(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/SimpleGameTest/move1jack(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/FirstSquare/player()|,|java+interface:///java/lang/Override|>
},
typeDependency={
<|java+method:///snakes/Game/winner()|,|java+class:///snakes/Game|>,
<|java+method:///snakes/Game/winner()|,|java+class:///snakes/Player|>,
<|java+parameter:///snakes/Player/joinGame(snakes.Game)/scope(game)/scope(0)/game|,|java+class:///snakes/Game|>,
<|java+field:///snakes/Game/winner|,|java+class:///snakes/Player|>,
<|java+method:///snakes/Square/nextSquare()|,|java+interface:///snakes/ISquare|>,
<|java+method:///snakes/Square/nextSquare()|,|java+class:///snakes/Game|>,
<|java+method:///snakes/Square/nextSquare()|,|java+primitiveType:///int|>,
<|java+method:///snakes/Square/nextSquare()|,|java+class:///snakes/Square|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+interface:///snakes/ISquare|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+class:///snakes/Game|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+primitiveType:///int|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+class:///snakes/Square|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+class:///java/lang/String|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+interface:///snakes/ISquare|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+class:///snakes/Game|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+class:///java/lang/Object|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+class:///Given|>,
<|java+method:///snakes/Game/initSquare(int,snakes.ISquare)|,|java+interface:///snakes/ISquare|>,
...

Next, let's focus on the containment relation. This defines what parts of the source code are parts of which other parts:

rascal>myModel.containment
rel[loc from,loc to]: {
<|java+method:///snakes/Game/isValidPosition(int)|,|java+parameter:///snakes/Game/isValidPosition(int)/scope(position)/scope(0)/position|>,
<|java+compilationUnit:///snakes-and-ladders/src/snakes/SimpleGameTest.java|,|java+class:///snakes/SimpleGameTest|>,
<|java+method:///snakes/Square/enter(snakes.Player)|,|java+parameter:///snakes/Square/enter(snakes.Player)/scope(player)/scope(0)/player|>,
<|java+method:///snakes/FirstSquare/leave(snakes.Player)|,|java+parameter:///snakes/FirstSquare/leave(snakes.Player)/scope(player)/scope(0)/player|>,
<|java+method:///snakes/Game/findSquare(int,int)|,|java+variable:///snakes/Game/findSquare(int,int)/target|>,
<|java+method:///snakes/Game/findSquare(int,int)|,|java+parameter:///snakes/Game/findSquare(int,int)/scope(position)/scope(0)/position|>,
<|java+method:///snakes/Game/findSquare(int,int)|,|java+parameter:///snakes/Game/findSquare(int,int)/scope(moves)/scope(0)/moves|>,
<|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|,|java+parameter:///snakes/Snake/Snake(int,snakes.Game,int)/scope(transport)/scope(0)/transport|>,
<|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|,|java+parameter:///snakes/Snake/Snake(int,snakes.Game,int)/scope(position)/scope(0)/position|>,
<|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|,|java+parameter:///snakes/Snake/Snake(int,snakes.Game,int)/scope(game)/scope(0)/game|>,
<|java+method:///snakes/Game/addPlayers(snakes.Player%5B%5D)|,|java+variable:///snakes/Game/addPlayers(snakes.Player%5B%5D)/scope(0)/player|>,
<|java+method:///snakes/Game/addPlayers(snakes.Player%5B%5D)|,|java+parameter:///snakes/Game/addPlayers(snakes.Player%5B%5D)/scope(initPlayers)/scope(0)/initPlayers|>,
<|java+compilationUnit:///snakes-and-ladders/src/snakes/Snake.java|,|java+class:///snakes/Snake|>,
<|java+compilationUnit:///snakes-and-ladders/src/snakes/Die.java|,|java+class:///snakes/Die|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+parameter:///snakes/Square/moveAndLand(int)/scope(moves)/scope(0)/moves|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+parameter:///snakes/SimpleGameTest/move1strings(snakes.Game)/scope(game)/scope(0)/game|>,
<|java+method:///snakes/Game/initSquare(int,snakes.ISquare)|,|java+parameter:///snakes/Game/initSquare(int,snakes.ISquare)/scope(square)/scope(0)/square|>,
<|java+method:///snakes/Game/initSquare(int,snakes.ISquare)|,|java+parameter:///snakes/Game/initSquare(int,snakes.ISquare)/scope(position)/scope(0)/position|>,
<|java+class:///snakes/Die|,|java+method:///snakes/Die/roll()|>,
<|java+class:///snakes/Die|,|java+field:///snakes/Die/FACES|>,
<|java+class:///snakes/Snake|,|java+method:///snakes/Snake/squareLabel()|>,
<|java+class:///snakes/Snake|,|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|>,
<|java+method:///snakes/Die/roll()|,|java+variable:///snakes/Die/roll()/result|>,
<|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,|java+parameter:///snakes/SimpleGameTest/initialStrings(snakes.Game)/scope(game)/scope(0)/game|>,
<|java+method:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)|,|java+parameter:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)/scope(game)/scope(0)/game|>,
<|java+method:///snakes/DieTest/reached(int)|,|java+variable:///snakes/DieTest/reached(int)/scope(0)/i|>,
<|java+method:///snakes/DieTest/reached(int)|,|java+variable:///snakes/DieTest/reached(int)/die|>,
<|java+method:///snakes/DieTest/reached(int)|,|java+parameter:///snakes/DieTest/reached(int)/scope(value)/scope(0)/value|>,
<|java+method:///snakes/Game/addSquares(int)|,|java+variable:///snakes/Game/addSquares(int)/scope(0)/scope(0)/square|>,
<|java+method:///snakes/Game/addSquares(int)|,|java+parameter:///snakes/Game/addSquares(int)/scope(size)/scope(0)/size|>,
<|java+method:///snakes/Game/addSquares(int)|,|java+variable:///snakes/Game/addSquares(int)/scope(0)/i|>,
<|java+method:///snakes/DieTest/testInRange()...

You are looking at a binary relation of type rel[loc from,loc to], where from is the container and to is the contained item. Each tuple, or row if you will, maps a container to a contained item.

As you can read, classes contain methods, methods contain variables, etc. Classes could also contain other classes (nested classes), and methods can even contain classes (anonymous classes). Let's focus on a specific class, and project what it contains from the relation:

rascal>import IO;
ok
rascal>println(readFile(|java+class:///snakes/Snake|))
public class Snake extends Ladder {

public Snake(int transport, Game game, int position) {
super(transport, game, position);
}

@Override
protected String squareLabel() {
return this.destination().position() + "<-" + position;
}

}
ok
rascal>myModel.containment[|java+class:///snakes/Snake|]
set[loc]: {
|java+method:///snakes/Snake/squareLabel()|,
|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|
}
rascal>methods(myModel)
set[loc]: {
|java+method:///snakes/Game/isValidPosition(int)|,
|java+method:///snakes/Game/firstSquare()|,
|java+method:///snakes/Square/enter(snakes.Player)|,
|java+constructor:///snakes/Player/Player(java.lang.String)|,
|java+method:///snakes/Game/setSquareToSnake(int,int)|,
|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,
|java+method:///snakes/Game/winner()|,
|java+method:///snakes/Square/nextSquare()|,
|java+method:///snakes/Square/moveAndLand(int)|,
|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,
|java+method:///snakes/Game/initSquare(int,snakes.ISquare)|,
|java+method:///snakes/Ladder/squareLabel()|,
|java+method:///snakes/FirstSquare/isOccupied()|,
|java+method:///snakes/Game/notOver()|,
|java+method:///snakes/Game/findSquare(int,int)|,
|java+method:///snakes/Player/wins()|,
|java+method:///snakes/DieTest/reached(int)|,
|java+method:///snakes/Square/previousSquare()|,
|java+method:///snakes/Die/roll()|,
|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)|,
|java+method:///snakes/Square/invariant()|,
|java+method:///snakes/ISquare/landHereOrGoHome()|,
|java+method:///snakes/Snake/squareLabel()|,
|java+method:///snakes/Game/addSquares(int)|,
|java+method:///snakes/DieTest/testInRange()|,
|java+method:///snakes/DieTest/testMinReached()|,
|java+method:///snakes/Game/toString()|,
|java+method:///snakes/Game/getSquare(int)|,
|java+method:///snakes/Square/isFirstSquare()|,
|java+method:///snakes/ISquare/isOccupied()|,
|java+method:///snakes/Player/square()|,
|java+method:///snakes/Game/play(snakes.Die)|,
|java+method:///snakes/Player/invariant()|,
|java+method:///snakes/ISquare/position()|,
|java+method:///snakes/Game/movePlayer(int)|,
|java+method:///snakes/Ladder/invariant()|,
|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|,
|java+method:///snakes/Game/main(java.lang.String%5B%5D)|,
|java+method:///snakes/Square/leave(snakes.Player)|,
|java+constructor:///snakes/Ladder/Ladder(int,snakes.Game,int)|,
|java+method:///snakes/Square/isLastSquare()|,
|java+constructor:///snakes/Square/Square(snakes.Game,int)|,
|java+method:///snakes/Ladder/landHereOrGoHome()|,
|java+constructor:///snakes/LastSquare/LastSquare(snakes.Game,int)|,
|java+method:///snakes/ISquare/moveAndLand(int)|,
|java+method:///snakes/Player/joinGame(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/newGame()|,
|java+method:///snakes/Square/player()|,
|java+method:///snakes/Game/setSquare(int,snakes.ISquare)|,
|java+method:///snakes/SimpleGameTest/move2jackBackwards(snakes.Game)|,
|java+method:///snakes/Game/currentPlayer()|,
|java+method:///snakes/Square/landHereOrGoHome()|,
|java+method:///snakes/Ladder/isValidTransport(int)|,
|java+method:///snakes/Player/position()|,
|java+method:///snakes/DieTest/testMaxReached()|,
|java+method:///snakes/SimpleGameTest/move5jackLadder(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move6jill(snakes.Game)|,
|java+method:///snakes/FirstSquare/enter(snakes.Player)|,
|java+method:///snakes/LastSquare/isLastSquare()|,
|java+method:///snakes/FirstSquare/leave(snakes.Player)|,
|java+method:///snakes/ISquare/isFirstSquare()|,
|java+method:///snakes/SimpleGameTest/move3jackMeetsJill(snakes.Game)|,
|java+method:///snakes/Square/isOccupied()|,
|java+method:///snakes/SimpleGameTest/move2jillLadder(snakes.Game)|,
|java+method:///snakes/Player/toString()|,
|java+method:///snakes/Game/isOver()|,
|java+method:///snakes/Ladder/destination()|,
|java+method:///snakes/Square/position()|,
|java+method:///snakes/Player/moveForward(int)|,
|java+method:///snakes/Game/invariant()|,
|java+method:///snakes/SimpleGameTest/move7jackBouncesBackToJill(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move1jack(snakes.Game)|,
|java+method:///snakes/FirstSquare/player()|,
|java+method:///snakes/Game/addPlayers(snakes.Player%5B%5D)...
rascal>import Set;
ok
rascal>size(methods(myModel))
int: 85

As you can see there are 85 methods in this system. Are they all used? That's not something you would want to check manually, so let's write some queries:

rascal>allMethods = methods(myModel);
set[loc]: {
|java+method:///snakes/Game/isValidPosition(int)|,
|java+method:///snakes/Game/firstSquare()|,
|java+method:///snakes/Square/enter(snakes.Player)|,
|java+constructor:///snakes/Player/Player(java.lang.String)|,
|java+method:///snakes/Game/setSquareToSnake(int,int)|,
|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,
|java+method:///snakes/Game/winner()|,
|java+method:///snakes/Square/nextSquare()|,
|java+method:///snakes/Square/moveAndLand(int)|,
|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,
|java+method:///snakes/Game/initSquare(int,snakes.ISquare)|,
|java+method:///snakes/Ladder/squareLabel()|,
|java+method:///snakes/FirstSquare/isOccupied()|,
|java+method:///snakes/Game/notOver()|,
|java+method:///snakes/Game/findSquare(int,int)|,
|java+method:///snakes/Player/wins()|,
|java+method:///snakes/DieTest/reached(int)|,
|java+method:///snakes/Square/previousSquare()|,
|java+method:///snakes/Die/roll()|,
|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)|,
|java+method:///snakes/Square/invariant()|,
|java+method:///snakes/ISquare/landHereOrGoHome()|,
|java+method:///snakes/Snake/squareLabel()|,
|java+method:///snakes/Game/addSquares(int)|,
|java+method:///snakes/DieTest/testInRange()|,
|java+method:///snakes/DieTest/testMinReached()|,
|java+method:///snakes/Game/toString()|,
|java+method:///snakes/Game/getSquare(int)|,
|java+method:///snakes/Square/isFirstSquare()|,
|java+method:///snakes/ISquare/isOccupied()|,
|java+method:///snakes/Player/square()|,
|java+method:///snakes/Game/play(snakes.Die)|,
|java+method:///snakes/Player/invariant()|,
|java+method:///snakes/ISquare/position()|,
|java+method:///snakes/Game/movePlayer(int)|,
|java+method:///snakes/Ladder/invariant()|,
|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|,
|java+method:///snakes/Game/main(java.lang.String%5B%5D)|,
|java+method:///snakes/Square/leave(snakes.Player)|,
|java+constructor:///snakes/Ladder/Ladder(int,snakes.Game,int)|,
|java+method:///snakes/Square/isLastSquare()|,
|java+constructor:///snakes/Square/Square(snakes.Game,int)|,
|java+method:///snakes/Ladder/landHereOrGoHome()|,
|java+constructor:///snakes/LastSquare/LastSquare(snakes.Game,int)|,
|java+method:///snakes/ISquare/moveAndLand(int)|,
|java+method:///snakes/Player/joinGame(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/newGame()|,
|java+method:///snakes/Square/player()|,
|java+method:///snakes/Game/setSquare(int,snakes.ISquare)|,
|java+method:///snakes/SimpleGameTest/move2jackBackwards(snakes.Game)|,
|java+method:///snakes/Game/currentPlayer()|,
|java+method:///snakes/Square/landHereOrGoHome()|,
|java+method:///snakes/Ladder/isValidTransport(int)|,
|java+method:///snakes/Player/position()|,
|java+method:///snakes/DieTest/testMaxReached()|,
|java+method:///snakes/SimpleGameTest/move5jackLadder(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move6jill(snakes.Game)|,
|java+method:///snakes/FirstSquare/enter(snakes.Player)|,
|java+method:///snakes/LastSquare/isLastSquare()|,
|java+method:///snakes/FirstSquare/leave(snakes.Player)|,
|java+method:///snakes/ISquare/isFirstSquare()|,
|java+method:///snakes/SimpleGameTest/move3jackMeetsJill(snakes.Game)|,
|java+method:///snakes/Square/isOccupied()|,
|java+method:///snakes/SimpleGameTest/move2jillLadder(snakes.Game)|,
|java+method:///snakes/Player/toString()|,
|java+method:///snakes/Game/isOver()|,
|java+method:///snakes/Ladder/destination()|,
|java+method:///snakes/Square/position()|,
|java+method:///snakes/Player/moveForward(int)|,
|java+method:///snakes/Game/invariant()|,
|java+method:///snakes/SimpleGameTest/move7jackBouncesBackToJill(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move1jack(snakes.Game)|,
|java+method:///snakes/FirstSquare/player()|,
|java+method:///snakes/Game/addPlayers(snakes.Player%5B%5D)...

methodInvocation reports on who calls who

rascal>myModel.methodInvocation
rel[loc from,loc to]: {
<|java+method:///snakes/Game/firstSquare()|,|java+method:///java/util/List/get(int)|>,
<|java+method:///snakes/Game/getSquare(int)|,|java+method:///snakes/Game/isValidPosition(int)|>,
<|java+method:///snakes/Game/getSquare(int)|,|java+method:///java/util/List/get(int)|>,
<|java+method:///snakes/Game/setSquareToSnake(int,int)|,|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|>,
<|java+method:///snakes/Game/setSquareToSnake(int,int)|,|java+method:///snakes/Game/setSquare(int,snakes.ISquare)|>,
<|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,|java+constructor:///java/util/ArrayList/ArrayList()|>,
<|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,|java+constructor:///snakes/Square/Square(snakes.Game,int)|>,
<|java+method:///snakes/FirstSquare/leave(snakes.Player)|,|java+method:///java/util/List/contains(java.lang.Object)|>,
<|java+method:///snakes/FirstSquare/leave(snakes.Player)|,|java+method:///java/util/List/remove(java.lang.Object)|>,
<|java+constructor:///snakes/Game/Game(int,snakes.Player%5B%5D)|,|java+method:///snakes/Game/addSquares(int)|>,
<|java+constructor:///snakes/Game/Game(int,snakes.Player%5B%5D)|,|java+method:///snakes/Game/invariant()|>,
<|java+constructor:///snakes/Game/Game(int,snakes.Player%5B%5D)|,|java+method:///snakes/Game/addPlayers(snakes.Player%5B%5D)|>,
<|java+method:///snakes/Square/nextSquare()|,|java+method:///snakes/Game/getSquare(int)|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/Game/findSquare(int,int)|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/ISquare/landHereOrGoHome()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///java/lang/Object/toString()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///snakes/Game/firstSquare()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///snakes/Game/getSquare(int)|>,
<|java+method:///snakes/Game/initSquare(int,snakes.ISquare)|,|java+method:///snakes/Game/isValidPosition(int)|>,
<|java+method:///snakes/Game/initSquare(int,snakes.ISquare)|,|java+method:///java/util/List/set(int,E)|>,
<|java+method:///snakes/FirstSquare/isOccupied()|,|java+method:///java/util/List/isEmpty()|>,
<|java+method:///snakes/Ladder/squareLabel()|,|java+method:///snakes/ISquare/position()|>,
<|java+method:///snakes/Ladder/squareLabel()|,|java+method:///snakes/Ladder/destination()|>,
<|java+method:///snakes/Game/findSquare(int,int)|,|java+method:///snakes/Game/getSquare(int)|>,
<|java+method:///snakes/Player/wins()|,|java+method:///snakes/ISquare/isLastSquare()|>,
<|java+method:///snakes/Square/previousSquare()|,|java+method:///snakes/Game/getSquare(int)|>,
<|java+method:///snakes/Die/roll()|,|java+method:///java/lang/Math/random()|>,
<|java+method:///snakes/DieTest/reached(int)|,|java+method:///snakes/Die/roll()|>,
<|java+method:///snakes/DieTest/reached(int)|,|java+constructor:///snakes/Die/Die()|>,
<|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,|java+method:///java/lang/Object/toString()|>,
<|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,|java+method:///snakes/Game/toString()|>,
<|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,|java+method:///snakes/Game/firstSquare()|>,
<|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,|java+method:///snakes/Game/getSquare(int)|>,
<|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,|java+method:///snakes/Player/toString()|>,
<|java+method:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)|,|java+method:///snakes/Game/notOver()|>,
<|java+method:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)|,|java+method:///snakes/Game/movePlayer(int)|>,
<|java+method:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)|,|java+method:///snakes/Game/currentPlayer()|>,
<|java+method:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)...

so let's find out which method definitions are never invoked

rascal>allMethods - myModel.methodInvocation<1>
set[loc]: {
|java+method:///snakes/Snake/squareLabel()|,
|java+method:///snakes/Square/enter(snakes.Player)|,
|java+method:///snakes/Ladder/landHereOrGoHome()|,
|java+method:///snakes/SimpleGameTest/move2jackBackwards(snakes.Game)|,
|java+method:///snakes/Square/position()|,
|java+method:///snakes/Square/toString()|,
|java+method:///snakes/SimpleGameTest/move8jillWins(snakes.Game)|,
|java+method:///snakes/Square/nextSquare()|,
|java+method:///snakes/Square/moveAndLand(int)|,
|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,
|java+method:///snakes/Ladder/squareLabel()|,
|java+method:///snakes/FirstSquare/isOccupied()|,
|java+method:///snakes/Square/previousSquare()|,
|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)|,
|java+method:///snakes/DieTest/testInRange()|,
|java+method:///snakes/DieTest/testMinReached()|,
|java+method:///snakes/Square/isFirstSquare()|,
|java+method:///snakes/Player/square()|,
|java+method:///snakes/Game/main(java.lang.String%5B%5D)|,
|java+method:///snakes/Square/leave(snakes.Player)|,
|java+method:///snakes/Square/isLastSquare()|,
|java+method:///snakes/Square/landHereOrGoHome()|,
|java+method:///snakes/DieTest/testMaxReached()|,
|java+method:///snakes/SimpleGameTest/move5jackLadder(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move6jill(snakes.Game)|,
|java+method:///snakes/FirstSquare/enter(snakes.Player)|,
|java+method:///snakes/LastSquare/isLastSquare()|,
|java+method:///snakes/FirstSquare/leave(snakes.Player)|,
|java+method:///snakes/SimpleGameTest/move3jackMeetsJill(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move2jillLadder(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move7jackBouncesBackToJill(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move1jack(snakes.Game)|,
|java+method:///snakes/FirstSquare/player()|,
|java+method:///snakes/FirstSquare/landHereOrGoHome()|,
|java+method:///snakes/FirstSquare/isFirstSquare()|
}

Mmmm... that's a lot! We've made a mistake. The Java language offers "virtual methods", while we have listed many method definitions that override virtual methods they are never explicitly called.


methodOverrides is a tabel that explains which method overrides which other method

rascal>myModel.methodOverrides
rel[loc from,loc to]: {
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/ISquare/moveAndLand(int)|>,
<|java+method:///snakes/Game/toString()|,|java+method:///java/lang/Object/toString()|>,
<|java+method:///snakes/Square/isFirstSquare()|,|java+method:///snakes/ISquare/isFirstSquare()|>,
<|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|,|java+constructor:///snakes/Ladder/Ladder(int,snakes.Game,int)|>,
<|java+method:///snakes/Square/enter(snakes.Player)|,|java+method:///snakes/ISquare/enter(snakes.Player)|>,
<|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,|java+constructor:///snakes/Square/Square(snakes.Game,int)|>,
<|java+method:///snakes/Square/landHereOrGoHome()|,|java+method:///snakes/ISquare/landHereOrGoHome()|>,
<|java+method:///snakes/Square/position()|,|java+method:///snakes/ISquare/position()|>,
<|java+method:///snakes/FirstSquare/player()|,|java+method:///snakes/Square/player()|>,
<|java+method:///snakes/Square/toString()|,|java+method:///java/lang/Object/toString()|>,
<|java+method:///snakes/Snake/squareLabel()|,|java+method:///snakes/Ladder/squareLabel()|>,
<|java+method:///snakes/Snake/squareLabel()|,|java+method:///snakes/Square/squareLabel()|>,
<|java+method:///snakes/FirstSquare/enter(snakes.Player)|,|java+method:///snakes/Square/enter(snakes.Player)|>,
<|java+method:///snakes/FirstSquare/enter(snakes.Player)|,|java+method:///snakes/ISquare/enter(snakes.Player)|>,
<|java+method:///snakes/Ladder/squareLabel()|,|java+method:///snakes/Square/squareLabel()|>,
<|java+method:///snakes/FirstSquare/isOccupied()|,|java+method:///snakes/ISquare/isOccupied()|>,
<|java+method:///snakes/FirstSquare/isOccupied()|,|java+method:///snakes/Square/isOccupied()|>,
<|java+method:///snakes/Square/leave(snakes.Player)|,|java+method:///snakes/ISquare/leave(snakes.Player)|>,
<|java+method:///snakes/Square/isLastSquare()|,|java+method:///snakes/ISquare/isLastSquare()|>,
<|java+constructor:///snakes/LastSquare/LastSquare(snakes.Game,int)|,|java+constructor:///snakes/Square/Square(snakes.Game,int)|>,
<|java+method:///snakes/Ladder/landHereOrGoHome()|,|java+method:///snakes/ISquare/landHereOrGoHome()|>,
<|java+method:///snakes/Ladder/landHereOrGoHome()|,|java+method:///snakes/Square/landHereOrGoHome()|>,
<|java+method:///snakes/LastSquare/isLastSquare()|,|java+method:///snakes/Square/isLastSquare()|>,
<|java+method:///snakes/LastSquare/isLastSquare()|,|java+method:///snakes/ISquare/isLastSquare()|>,
<|java+method:///snakes/FirstSquare/leave(snakes.Player)|,|java+method:///snakes/Square/leave(snakes.Player)|>,
<|java+method:///snakes/FirstSquare/leave(snakes.Player)|,|java+method:///snakes/ISquare/leave(snakes.Player)|>,
<|java+method:///snakes/Square/isOccupied()|,|java+method:///snakes/ISquare/isOccupied()|>,
<|java+method:///snakes/Player/toString()|,|java+method:///java/lang/Object/toString()|>,
<|java+method:///snakes/FirstSquare/landHereOrGoHome()|,|java+method:///snakes/ISquare/landHereOrGoHome()|>,
<|java+method:///snakes/FirstSquare/landHereOrGoHome()|,|java+method:///snakes/Square/landHereOrGoHome()|>,
<|java+method:///snakes/FirstSquare/isFirstSquare()|,|java+method:///snakes/Square/isFirstSquare()|>,
<|java+method:///snakes/FirstSquare/isFirstSquare()|,|java+method:///snakes/ISquare/isFirstSquare()|>
}

so we can compose that to find out who is probably called:

rascal>myModel.methodInvocation o (myModel.methodOverrides<1,0>) 
rel[loc,loc]: {
<|java+method:///snakes/Ladder/squareLabel()|,|java+method:///snakes/Square/position()|>,
<|java+method:///snakes/Snake/squareLabel()|,|java+method:///snakes/Square/position()|>,
<|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|,|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|>,
<|java+method:///snakes/Game/setSquareToLadder(int,int)|,|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|>,
<|java+method:///snakes/Player/wins()|,|java+method:///snakes/Square/isLastSquare()|>,
<|java+method:///snakes/Player/wins()|,|java+method:///snakes/LastSquare/isLastSquare()|>,
<|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,|java+method:///snakes/Game/toString()|>,
<|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,|java+method:///snakes/Player/toString()|>,
<|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,|java+method:///snakes/Square/toString()|>,
<|java+constructor:///snakes/Ladder/Ladder(int,snakes.Game,int)|,|java+constructor:///snakes/LastSquare/LastSquare(snakes.Game,int)|>,
<|java+constructor:///snakes/Ladder/Ladder(int,snakes.Game,int)|,|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|>,
<|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,|java+constructor:///snakes/LastSquare/LastSquare(snakes.Game,int)|>,
<|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|>,
<|java+method:///snakes/SimpleGameTest/move3jackMeetsJill(snakes.Game)|,|java+method:///snakes/FirstSquare/isOccupied()|>,
<|java+method:///snakes/SimpleGameTest/move3jackMeetsJill(snakes.Game)|,|java+method:///snakes/Square/isOccupied()|>,
<|java+method:///snakes/Player/moveForward(int)|,|java+method:///snakes/Square/moveAndLand(int)|>,
<|java+method:///snakes/Player/moveForward(int)|,|java+method:///snakes/Square/enter(snakes.Player)|>,
<|java+method:///snakes/Player/moveForward(int)|,|java+method:///snakes/Square/leave(snakes.Player)|>,
<|java+method:///snakes/Player/moveForward(int)|,|java+method:///snakes/FirstSquare/enter(snakes.Player)|>,
<|java+method:///snakes/Player/moveForward(int)|,|java+method:///snakes/FirstSquare/leave(snakes.Player)|>,
<|java+method:///snakes/Square/toString()|,|java+method:///snakes/Ladder/squareLabel()|>,
<|java+method:///snakes/Square/toString()|,|java+method:///snakes/Snake/squareLabel()|>,
<|java+method:///snakes/Square/toString()|,|java+method:///snakes/FirstSquare/player()|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/Ladder/landHereOrGoHome()|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/Square/landHereOrGoHome()|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/FirstSquare/landHereOrGoHome()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///snakes/Game/toString()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///snakes/Player/toString()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///snakes/Square/toString()|>,
<|java+method:///snakes/Game/addSquares(int)|,|java+constructor:///snakes/LastSquare/LastSquare(snakes.Game,int)|>,
<|java+method:///snakes/Game/addSquares(int)|,|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|>,
<|java+method:///snakes/Game/toString()|,|java+method:///snakes/Game/toString()|>,
<|java+method:///snakes/Game/toString()|,|java+method:///snakes/Player/toString()|>,
<|java+method:///snakes/Game/toString()|,|java+method:///snakes/Square/toString()|>,
<|java+method:///snakes/Ladder/landHereOrGoHome()|,|java+method:///snakes/Ladder/landHereOrGoHome()|>,
<|java+method:///snakes/Ladder/landHereOrGoHome()|,|java+method:///snakes/Square/landHereOrGoHome()|>,
<|java+method:///snakes/Ladder/landHereOrGoHome()|,|java+method:///snakes/FirstSquare/landHereOrGoHome()...

and by adding all the others as well, we have a "complete" call graph

rascal>calls = myModel.methodInvocation + myModel.methodInvocation o (myModel.methodOverrides<1,0>);
rel[loc,loc]: {
<|java+method:///snakes/Game/firstSquare()|,|java+method:///java/util/List/get(int)|>,
<|java+method:///snakes/Game/getSquare(int)|,|java+method:///snakes/Game/isValidPosition(int)|>,
<|java+method:///snakes/Game/getSquare(int)|,|java+method:///java/util/List/get(int)|>,
<|java+method:///snakes/Game/setSquareToSnake(int,int)|,|java+constructor:///snakes/Snake/Snake(int,snakes.Game,int)|>,
<|java+method:///snakes/Game/setSquareToSnake(int,int)|,|java+method:///snakes/Game/setSquare(int,snakes.ISquare)|>,
<|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,|java+constructor:///java/util/ArrayList/ArrayList()|>,
<|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|>,
<|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,|java+constructor:///snakes/Square/Square(snakes.Game,int)|>,
<|java+constructor:///snakes/FirstSquare/FirstSquare(snakes.Game,int)|,|java+constructor:///snakes/LastSquare/LastSquare(snakes.Game,int)|>,
<|java+method:///snakes/FirstSquare/leave(snakes.Player)|,|java+method:///java/util/List/contains(java.lang.Object)|>,
<|java+method:///snakes/FirstSquare/leave(snakes.Player)|,|java+method:///java/util/List/remove(java.lang.Object)|>,
<|java+constructor:///snakes/Game/Game(int,snakes.Player%5B%5D)|,|java+method:///snakes/Game/addSquares(int)|>,
<|java+constructor:///snakes/Game/Game(int,snakes.Player%5B%5D)|,|java+method:///snakes/Game/invariant()|>,
<|java+constructor:///snakes/Game/Game(int,snakes.Player%5B%5D)|,|java+method:///snakes/Game/addPlayers(snakes.Player%5B%5D)|>,
<|java+method:///snakes/Square/nextSquare()|,|java+method:///snakes/Game/getSquare(int)|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/Game/findSquare(int,int)|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/ISquare/landHereOrGoHome()|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/Ladder/landHereOrGoHome()|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/Square/landHereOrGoHome()|>,
<|java+method:///snakes/Square/moveAndLand(int)|,|java+method:///snakes/FirstSquare/landHereOrGoHome()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///java/lang/Object/toString()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///snakes/Game/toString()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///snakes/Game/firstSquare()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///snakes/Game/getSquare(int)|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///snakes/Player/toString()|>,
<|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,|java+method:///snakes/Square/toString()|>,
<|java+method:///snakes/Game/initSquare(int,snakes.ISquare)|,|java+method:///snakes/Game/isValidPosition(int)|>,
<|java+method:///snakes/Game/initSquare(int,snakes.ISquare)|,|java+method:///java/util/List/set(int,E)|>,
<|java+method:///snakes/FirstSquare/isOccupied()|,|java+method:///java/util/List/isEmpty()|>,
<|java+method:///snakes/Ladder/squareLabel()|,|java+method:///snakes/ISquare/position()|>,
<|java+method:///snakes/Ladder/squareLabel()|,|java+method:///snakes/Ladder/destination()|>,
<|java+method:///snakes/Ladder/squareLabel()|,|java+method:///snakes/Square/position()|>,
<|java+method:///snakes/Game/findSquare(int,int)|,|java+method:///snakes/Game/getSquare(int)|>,
<|java+method:///snakes/Player/wins()|,|java+method:///snakes/Square/isLastSquare()|>,
<|java+method:///snakes/Player/wins()|,|java+method:///snakes/LastSquare/isLastSquare()|>,
<|java+method:///snakes/Player/wins()|,|java+method:///snakes/ISquare/isLastSquare()|>,
<|java+method:///snakes/Square/previousSquare()|,|java+method:///snakes/Game/getSquare(int)...

so which methods are defined but never called int this Game?

rascal>notCalled = methods(myModel) - calls<1>;
set[loc]: {
|java+method:///snakes/Player/square()|,
|java+method:///snakes/Game/main(java.lang.String%5B%5D)|,
|java+method:///snakes/SimpleGameTest/move2jackBackwards(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move6jill(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move8jillWins(snakes.Game)|,
|java+method:///snakes/Square/nextSquare()|,
|java+method:///snakes/SimpleGameTest/move1strings(snakes.Game)|,
|java+method:///snakes/Square/previousSquare()|,
|java+method:///snakes/SimpleGameTest/initialStrings(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move4jillSnake(snakes.Game)|,
|java+method:///snakes/DieTest/testInRange()|,
|java+method:///snakes/DieTest/testMinReached()|,
|java+method:///snakes/DieTest/testMaxReached()|,
|java+method:///snakes/SimpleGameTest/move5jackLadder(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move3jackMeetsJill(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move2jillLadder(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move7jackBouncesBackToJill(snakes.Game)|,
|java+method:///snakes/SimpleGameTest/move1jack(snakes.Game)|
}
rascal>notConstructed = constructors(myModel) - calls<1>;
set[loc]: {}

The results are:

  • main is not called; that makes sense
  • lots of test methods are not called; that also makes sense since they are called by the Unit test framework using reflection;
  • we can filter the tests automatically, but this set is small enough to go through manually.

The two unused methods are:

  • |java+method:///snakes/Square/nextSquare()|
  • |java+method:///snakes/Player/square()|

In an interactive environment like Eclipse or VScode we would click on these links to jump to their source code. Here we will print the bodies:

rascal>println(readFile(|java+method:///snakes/Player/square()|))
public ISquare square() {
return square;
}
ok
rascal>println(readFile(|java+method:///snakes/Square/nextSquare()|))
protected ISquare nextSquare() {
return game.getSquare(position+1);
}
ok

Note that this analysis is reasonably precise, but not 100% exact:

  • all name analysis and type analysis is done and used to disambiguate identifier names. There can be no confusion between overloaded methods for example and therefore overriding/implementing analysis is exact.
  • the constructed call graph is:
    • an over-approximation because not all overriden methods have to be called, it's just that they might be called
    • an under-approximation because we don't see the calls made by reflection. The test methods are a good example of that
  • adding more analysis code can make the result more exact.