[Demonstration 1]

[Buggy Method]
public ArrayList<Task> redo() {
    if (!redoStack.isEmpty()) {
        ArrayList<Task> previousState = redoStack.pop();
        undoStack.push(previousState);
        return redoStack.peek();
    }
    return initialState;
}

[Buggy Hunk]
return redoStack.peek();

[Patch]
return undoStack.peek();

[Demonstration 2]

[Buggy Method]
public static void main(String[] args) {
    GoBangGame gbg = GoBangGame.getInstance();
}

[Buggy Hunk]
GoBangGame gbg = GoBangGame.getInstance();

[Patch]
GoBangGame.getInstance();

[Demonstration 3]

[Buggy Method]
@Override
public void execute() {
    display.push(cmd);
}

[Buggy Hunk]
display.push(cmd);

[Patch]
display.push(b.getLabel());