// @(#)$Id: Comparable.spec,v 1.17 2007/02/08 17:28:04 leavens Exp $
// Copyright (C) 2005 Iowa State University
//
// This file is part of the runtime library of the Java Modeling Language.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public License
// as published by the Free Software Foundation; either version 2.1,
// of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with JML; see the file LesserGPL.txt. If not, write to the Free
// Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
// 02110-1301 USA.
package java.lang;
/** JML's specification of java.lang.Comparable.
* These are objects with a total ordering that is an equivalence relation.
* @version $Revision: 1.17 $
* @author Gary T. Leavens
*/
public interface Comparable {
/*@ public normal_behavior
@ requires i < 0;
@ ensures \result == -1;
@ also
@ public normal_behavior
@ requires i == 0;
@ ensures \result == 0;
@ also
@ public normal_behavior
@ requires i >= 0;
@ ensures \result == +1;
@ implies_that
@ public model_program {
@ return ((i < 0) ? -1 : ((i == 0) ? 0 : 1));
@ }
@ model pure int sgn(int i);
@*/
/*@ public model_program {
@ boolean x_y_def = true;
@ try {
@ x.compareTo(y);
@ } catch (ClassCastException e) {
@ x_y_def = false;
@ }
@ return x_y_def;
@ }
@ also public normal_behavior
@ ensures \result == definedComparison(y,x);
@ public model pure boolean
@ definedComparison(non_null Comparable x, non_null Comparable y);
@*/
/* Returns an indication of how the argument compares to this
* object. Note that although the documentation describes the
* behavior when null is passed as an argument (this method
* should throw a NullPointerException), we have decided to
* specify the method as not allowing null as an argument.
* So the non_null on the argument is not a mistake.
*/
/*@ public behavior
@ requires o != null;
@ ensures (* \result is negative if this is "less than" o *);
@ ensures (* \result is 0 if this is "equal to" o *);
@ ensures (* \result is positive if this is "greater than" o *);
@ signals_only ClassCastException;
@ signals (ClassCastException)
@ (* the class of o prohibits it from being compared to this *);
@ also
@ public behavior
@ requires o != null && o instanceof Comparable;
@ ensures definedComparison((Comparable)o, this);
@ ensures o == this ==> \result == 0; // reflexive
@ ensures sgn(\result) == - sgn(((Comparable)o).compareTo(this)); // antisymmetric
@ signals(ClassCastException)
@ !definedComparison((Comparable)o, this);
@*/
/*@ pure @*/ int compareTo(/*@ non_null @*/ Object o);
// compareTo is reflexive
/*+@ public instance invariant
@ (\forall Comparable x; x != null; x.compareTo(x) == 0);
@*/
// compareTo is antisymmetric
/*+@ public instance invariant
@ (\forall Comparable x, y; x != null && y != null
@ && definedComparison(x, y)
@ && definedComparison(y, x);
@ sgn(x.compareTo(y)) == -sgn(y.compareTo(x)) );
@*/
// compareTo is transitive
/*+@ public instance invariant
@ (\forall int n; n == -1 || n == 1;
@ (\forall Comparable x, y, z;
@ x != null && y != null && z != null
@ && definedComparison(x, y) && definedComparison(y, z)
@ && definedComparison(x, z);
@ sgn(x.compareTo(y)) == n && sgn(y.compareTo(z)) == n
@ ==> sgn(x.compareTo(z)) == n));
@ public instance invariant
@ (\forall int n; n == -1 || n == 1;
@ (\forall Comparable x, y, z;
@ x != null && y != null && z != null
@ && definedComparison(x, y) && definedComparison(y, z)
@ && definedComparison(x, z);
@ (sgn(x.compareTo(y)) == 0 && sgn(y.compareTo(z)) == n
@ || sgn(x.compareTo(y)) == n && sgn(y.compareTo(z)) == 0)
@ ==> sgn(x.compareTo(z)) == n));
@*/
// compareTo returning 0 means the other argument
// is in the same equivalence class
/*+@ public instance invariant
@ (\forall Comparable x, y, z;
@ x != null && y != null && z != null
@ && definedComparison(x, y) && definedComparison(x, z)
@ && definedComparison(y, z);
@ sgn(x.compareTo(y)) == 0
@ ==> sgn(x.compareTo(z)) == sgn(y.compareTo(z)));
@*/
}