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/**************************************************************************/
/* */
/* The Why platform for program certification */
/* */
/* Copyright (C) 2002-2011 */
/* */
/* Jean-Christophe FILLIATRE, CNRS & Univ. Paris-sud 11 */
/* Claude MARCHE, INRIA & Univ. Paris-sud 11 */
/* Yannick MOY, Univ. Paris-sud 11 */
/* Romain BARDOU, Univ. Paris-sud 11 */
/* */
/* Secondary contributors: */
/* */
/* Thierry HUBERT, Univ. Paris-sud 11 (former Caduceus front-end) */
/* Nicolas ROUSSET, Univ. Paris-sud 11 (on Jessie & Krakatoa) */
/* Ali AYAD, CNRS & CEA Saclay (floating-point support) */
/* Sylvie BOLDO, INRIA (floating-point support) */
/* Jean-Francois COUCHOT, INRIA (sort encodings, hyps pruning) */
/* Mehdi DOGGUY, Univ. Paris-sud 11 (Why GUI) */
/* */
/* This software is free software; you can redistribute it and/or */
/* modify it under the terms of the GNU Lesser General Public */
/* License version 2.1, with the special exception on linking */
/* described in file LICENSE. */
/* */
/* This software 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. */
/* */
/**************************************************************************/
//@+ CheckArithOverflow = no
class NoCreditException extends Exception {
public NoCreditException() { }
}
public class Purse {
static NoCreditException noCreditException = new NoCreditException();
private int balance;
//@ invariant balance_positive: balance > 0;
/*@ requires amount > 0;
@ assigns balance;
@ ensures balance == amount;
@*/
public Purse(int amount) {
balance = amount;
}
/*@ requires s >= 0;
@ assigns balance;
@ ensures balance == \old(balance) + s;
@*/
public void credit(int s) {
balance += s;
}
/*@ requires s >= 0;
@ assigns balance;
@ ensures s < \old(balance) && balance == \old(balance) - s;
@ behavior amount_too_large:
@ assigns \nothing;
@ signals (NoCreditException)
@ s >= \old(balance) ;
@*/
public void withdraw(int s) throws NoCreditException {
if (s < balance)
balance = balance - s;
else
throw noCreditException;
}
/*@ requires p != null && s >= 0;
@ behavior transfer_ok:
@ ensures
@ balance == \old(balance) - s &&
@ p.balance == \old(p.balance) + s &&
@ \result == balance;
@ behavior transfer_failed:
@ signals (NoCreditException)
@ balance == \old(balance) &&
@ p.balance == \old(p.balance);
@*/
public int transfer_to(Purse p, int s) throws NoCreditException {
p.credit(s);
withdraw(s);
return balance;
}
}
/*
Local Variables:
compile-command: "make Purse"
End:
*/
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