design by contract using jmsassert. design by contract a method of separating the concerns of the...

Design By ContractDesign By Contract

Using JMSAssert

Design By ContractDesign By Contract A method of separating the concerns of the

user and implementer of the class, and giving both enough information for their tasks.

Work in this course will be done with Java, offers partial support for those concepts.

Each class and method should be documented in Javadoc style.

Design By ContractDesign By Contract In order to implement the principles of Design-by-

Contract in Java, we will use a free tool from Man Machine Systems names JMSAssert.

It works with Sun’s JDK 1.2 & 1.3 but not 1.4

Design By ContractDesign By Contract A powerful technique for writing reliable

software. Specifying the software purpose with the

implementation. Key elements:

Invariant Preconditions Postconditions

Design By ContractDesign By Contract Precondition – The constraints under

which the routine will function properly. Postconditions – The state of the class after

the routine execution The Contract: If you call routine R() with

the preconditions satisfied, R() will return satisfying the postconditions.

Invariant – Always holds

When are condition checked?When are condition checked?

Event InvariantPre-

conditionPost-

conditionInstance Method Y Y -Constructor N Y -Private Method N Y -Static Method N Y -Instance Method Y - YConstructor Y - YPrivate Method N - YStatic Method N - Y

Method Entry

Method Exit

JMS Syntax - InvariantJMS Syntax - Invariant Invariant - @inv May access all class members or its

direct/indirect bases, including private members

May appear in any JavaDoc comment Preferable in the class comment

JMS Syntax - PreconditionsJMS Syntax - Preconditions Precondition - @pre JavaDoc preceding the respective method May reference class members and

arguments Multiple @pre markers are conjugated

(AND)

JMS Syntax - PostconditionsJMS Syntax - Postconditions Postconditions - @post JavaDoc preceding the respective method May use $prev(expression) to access the

value at the method entry. May use $ret to denote method’s return

value Multiple @post markers are conjugated

(AND)

ExampleExample

/** * @pre !isEmpty() * @post (top == $prev(top- 1)) * @post $ret == elems[top] * @post !isFull*/public synchronized Object pop() {

return elems[--top];}

Precondition

Postconditions

ExampleExample

/** * @pre !isEmpty() * @post (top == $prev(top- 1)) * @post $ret == elems[top] * @post !isFull*/public synchronized Object pop() {

return elems[--top];}

Precondition

Postconditions

What is wrong in the example ?

JMS Syntax - GeneralJMS Syntax - General Order has no meaning @macro – for complicated conditions Recursion – as expected, on every call Inner classes can access outer classes’

members Anonymous classes – specify invariant in

one of its methods

Downloads & InstallationsDownloads & Installations Download Java J2SE SDK 1.3.1 from

http://java.sun.com/downloads (~41MB)Install into C:\Program Files\jdk1.3.1_07

Download JMSAssert 1.02 from http://www.mmsindia.com (~1.2MB)Run the jmssetup-1.02.exe installation fileInstall into C:\Program Files\AMSAssert1.0

JMSAssert InstallationJMSAssert Installation The following lines are added to the path:REM Next two lines are added by JMSAssert

SET CLASSPATH=%CLASSPATH%;C:\PROGRA~1\JMSASS~1.0\

bin\mmsclasses.jar;

SET PATH=%PATH%;C:\PROGRA~1\JMSASS~1.0\bin;

Copy the “classic” directory from “C:\Program Files\jdk1.3.1_07\jre\bin\” to the directory:“C:\Program Files\JavaSoft\JRE\1.3.1_07\bin\”

Setup Setup (cont.)(cont.)

Your JavaSoft directory should look like:

JMSAssert – how does it workJMSAssert – how does it work Annotate source code with assertions Compile your code using javac (as usual) Preprocess the code using jmsassert: creates

contract files (*.jms) and a Startup.jms file. *.jms files contain java code for the assertions. Execute using: jmsjava Startup <filename>to check assertions.

jmsjava makes sure method assertions are called before/after the method invocation.

JMS ExecutionJMS Execution “jmsassert” – generates help text “jmsassert –s <filename.java>” – generate

assertions for a class file “jmsassert –r –s .” – generate assertions for

all class files in the directory and sub-dirs. (use for packages)

“javac <filename.java>” – compile “jmsjava Startup <main>” - execute and check

assertions

Annotate source with assertions

MyStack.java

Stack Demo Stack Demo filesfiles

Execution Execution processprocess


Preprocess to generate assertion

filesjmsassert –s <file.java>

MyStack.java

Startup.jms

default_MyStack.jmsdefault_MyStack_StackEnum.jms






Compile Java file

javac <file.java<

MyStack.java

Startup.jms


MyStack.classMyStack$StackEnum.classMyStack$StackEnum.classStackTest.class






Compile Java file

javac <file.java<

Execute using jmsjava

MyStack.java

Startup.jms


MyStack.classMyStack$StackEnum.classMyStack$StackEnum.classjmsjava Startup <classname> StackTest.class



NotesNotes Execute these steps form the command line! Make sure your CLASSPATH environment

variable contains the current directory.Add “CLASSPATH=%CLASSPATH%;.” to autoexec.bat.

An Example (MyStack)An Example (MyStack) A stack with invariants, pre conditions and post

conditions: MyStack.java A main file: StackTest.java Compile all .java files (using javac) Generate JMSAssert triggers by:jmsassert –s MyStack.java

Run and test assertions byjmsjava Startup StackTest

You can always run your test program in byjava StackTest

MyStack.java (#1)MyStack.java (#1)/**

@inv (top >= 0 && top < max)

*/

class MyStack {

private Object[] elems;

private int top, max;

MyStack.java (#2)MyStack.java (#2).

/**

@pre (sz > 0)

@post (max == sz && elems != null)

*/

public MyStack(int sz) {

max = sz;

elems = new Object[sz];

}

MyStack.java (#3)MyStack.java (#3)

/**

@pre !isFull()

@post (top == $prev (top) + 1) && elems[top-1] == obj

*/

public void push(Object obj) {

elems[top++] = obj;

}


/**

@pre !isEmpty()

@post (top == $prev (top) - 1) && $ret == elems[top]

*/

public Object pop() {

return elems[--top];

}


/**

@post ($ret == (top == max))

*/

public boolean isFull()

{

return top == max;

}


/**

@post ($ret == (top == 0))

*/

public boolean isEmpty()

{

return top == 0;

}

} // End MyStack

StackTest.javaStackTest.java

class StackTest {

public static void main(String[] args) {

MyStack s = new MyStack(2); // Can push at most 2 elements

s.push(new Integer(1));

s.push(new Integer(23));

s.push(new Integer(0)); // Precondition violation here!

}

}

design by contract using jmsassert. design by contract a method of separating the concerns of the...

Documents

max slide

jmsassert slide

post max

class comment slide

post javadoc

end mystack slide

post markers

return elems