fix warnings

app/src/main/java/sudoku/structure/Sudoku.java

@@ -1,13 +1,11 @@
 package sudoku.structure;
 
-import sudoku.constraint.BlockConstraint;
-import sudoku.constraint.Constraint;
-import sudoku.constraint.IConstraint;
-import sudoku.io.SudokuPrinter;
-
 import java.util.ArrayList;
 import java.util.List;
 
+import sudoku.constraint.Constraint;
+import sudoku.constraint.IConstraint;
+
 /**
  * @class Sudoku
  * @brief Représent un Sudoku
@@ -309,7 +307,7 @@ public class Sudoku {
 	}
 
 	public boolean hasConstraint(Constraint constraint) {
-		return this.constraints.contains(constraint);
+		return this.constraints.contains(constraint.getConstraint());
 	}
 
 }