docs/tutorial/webpages/get-started-cmd.html - typetools/checker-framework - Git at Google

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   <div class="page-header short" style=
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     <h1>Checker Framework Tutorial</h1>
   </div>

   <div id="gettingstarteed">
     <div class="page-header short" style="border-top: none;">
       <h2>Getting Started</h2>
     </div>

     <div class="section">
       <p>This page walks you through a simple example to show how to use a
       type-checker
       from the command line.
       It shows how the Nullness
       Checker can be used to prevent null pointer exceptions.</p>
     </div>

     <div class="section">
       <h4>Outline</h4>

       <div class="well">
         <ol>
           <li><a href="#view">Manually spot the null pointer
           exception</a></li>

           <li><a href="#run1">Run the Nullness Checker to see how it can
           catch this error</a></li>

           <li><a href="#error">Correct the error</a></li>

           <li><a href="#run2">Run the Nullness Checker to verify that
           there are no more errors</a></li>
         </ol>
       </div>

       <div id="view">
         <h4>1. Spot the null pointer exception</h4>Begin by <b>viewing
         <a href=
         "../src/NullnessExample.java">NullnessExample.java</a></b>. (If
         you have not already, download <a href="../sourcefiles.zip">the
         source files</a> for the tutorial.)
         It is a simple Java program with an obvious null pointer exception.
         <pre>
 public class NullnessExample {
     public static void main(String[] args) {
         Object myObject = null;
         System.out.println(myObject.toString());
     }
 }
 </pre>
       </div>

       <div id="run1">
         <h4>2. Run the Nullness Checker</h4>

         <p><b>Run the Nullness Checker</b> to see how it can warn you
         about this error at compile time.</p>

         <p>To run the Nullness Checker, run javac with command-line
         arguments <code>-processor
         org.checkerframework.checker.nullness.NullnessChecker</code>, as
         follows.</p>

         <p>(Note:  In this tutorial, the commands that you cut-and-paste
         to run on the command line appear in bold after a <code>$</code> prompt.)
         <br/>
         (Note: You should have already made
         <code>javacheck</code> <a href=
         "https://checkerframework.org/manual/#installation">
         an alias</a> to the Checker Framework compiler.)</p>
         <pre>
 $ <strong>javacheck -processor org.checkerframework.checker.nullness.NullnessChecker NullnessExample.java</strong>
 </pre>

         <p>The following error will be produced.</p>
         <pre>
 NullnessExample.java:9: error: [dereference.of.nullable] dereference of possibly-null reference myObject
         System.out.println(myObject.toString());
                            ^
 1 error
 </pre>
       </div>

       <div id="error">
         <h4>3. Correct the error</h4>

         <p>Edit the code to <b>initialize the <code>myObject</code> variable</b>
         to some non-null value.</p>
         <pre>
 public class NullnessExample {
     public static void main(String[] args) {
         Object myObject = <b>new Object()</b>;
         System.out.println(myObject.toString());
     }
 }
 </pre>
       </div>

       <div id="run2">
         <h4>4. Re-run the Nullness Checker</h4>
         <pre>
 $ <b>javacheck -processor org.checkerframework.checker.nullness.NullnessChecker NullnessExample.java</b>
 </pre>

         <p>No errors should be produced.</p>
       </div>

       <p>This was a very simple example to show how to use the Checker Framework
       from the command line.
       The next example is a little more complex.</p>
     </div>
   </div>

   <div id="end">
     <div class="page-header short">
       <h2><small>Next, try <a href="user-input-cmd.html">Validating
       User Input</a>, an example using the Regex Checker.</small></h2>
     </div>
   </div><!--
 <div class="bottom_liner well">
     <a href="#">Top</a>
 </div>
 -->
   <!--  LocalWords:  Plugin plugin VM SDK plugins quals classpath
  -->
   <!--  LocalWords:  NullnessChecker plugin's hg
  -->
 </body>
 </html>
	<!DOCTYPE html>
	<html>
	<head>
	<meta name="generator" content=
	"HTML Tidy for Linux (vers 25 March 2009), see www.w3.org">

	<title>Checker Framework Tutorial - Getting Started - Command
	Line</title>
	<link href="bootstrap/css/bootstrap.css" rel="stylesheet" type=
	"text/css">
	<script type="text/javascript" src="bootstrap/js/bootstrap.min.js">
	</script>
	<link href="css/main.css" rel="stylesheet" type="text/css">
	<link rel="icon" type="image/png" href=
	"https://checkerframework.org/favicon-checkerframework.png">
	</head>

	<body>
	<div class="top_liner"></div>

	<div class="navbar navbar-inverse navbar-fixed-top" style=
	"border-bottom: 1px solid #66d;">
	<div class="navbar-inner">
	<div class="contained">
	<ul class="nav">
	<li class="heading">Checker Framework:</li>

	<li><a href="https://checkerframework.org/">Main Site</a></li>

	<li><a href=
	"https://checkerframework.org/manual/">
	Manual</a></li>

	<li><a href=
	"https://groups.google.com/forum/#!forum/checker-framework-discuss">
	Discussion List</a></li>

	<li><a href=
	"https://github.com/typetools/checker-framework/issues">Issue
	Tracker</a></li>

	<li><a href=
	"https://github.com/typetools/checker-framework">Source
	Code</a></li>

	<li class="active"><a href=
	"https://checkerframework.org/tutorial/">Tutorial</a></li>
	</ul>
	</div>
	</div>
	</div><img src="https://checkerframework.org/CFLogo.png" alt="Checker Framework logo">

	<div class="page-header short" style=
	"border-bottom: 1px solid #EEE; border-top: none;">
	<h1>Checker Framework Tutorial</h1>
	</div>

	<div id="gettingstarteed">
	<div class="page-header short" style="border-top: none;">
	<h2>Getting Started</h2>
	</div>

	<div class="section">
	<p>This page walks you through a simple example to show how to use a
	type-checker
	from the command line.
	It shows how the Nullness
	Checker can be used to prevent null pointer exceptions.</p>
	</div>

	<div class="section">
	<h4>Outline</h4>

	<div class="well">
	<ol>
	<li><a href="#view">Manually spot the null pointer
	exception</a></li>

	<li><a href="#run1">Run the Nullness Checker to see how it can
	catch this error</a></li>

	<li><a href="#error">Correct the error</a></li>

	<li><a href="#run2">Run the Nullness Checker to verify that
	there are no more errors</a></li>
	</ol>
	</div>

	<div id="view">
	<h4>1. Spot the null pointer exception</h4>Begin by <b>viewing
	<a href=
	"../src/NullnessExample.java">NullnessExample.java</a></b>. (If
	you have not already, download <a href="../sourcefiles.zip">the
	source files</a> for the tutorial.)
	It is a simple Java program with an obvious null pointer exception.
	<pre>
	public class NullnessExample {
	public static void main(String[] args) {
	Object myObject = null;
	System.out.println(myObject.toString());
	}
	}
	</pre>
	</div>

	<div id="run1">
	<h4>2. Run the Nullness Checker</h4>

	<p><b>Run the Nullness Checker</b> to see how it can warn you
	about this error at compile time.</p>

	<p>To run the Nullness Checker, run javac with command-line
	arguments <code>-processor
	org.checkerframework.checker.nullness.NullnessChecker</code>, as
	follows.</p>

	<p>(Note: In this tutorial, the commands that you cut-and-paste
	to run on the command line appear in bold after a <code>$</code> prompt.)
	<br/>
	(Note: You should have already made
	<code>javacheck</code> <a href=
	"https://checkerframework.org/manual/#installation">
	an alias</a> to the Checker Framework compiler.)</p>
	<pre>
	$ <strong>javacheck -processor org.checkerframework.checker.nullness.NullnessChecker NullnessExample.java</strong>
	</pre>

	<p>The following error will be produced.</p>
	<pre>
	NullnessExample.java:9: error: [dereference.of.nullable] dereference of possibly-null reference myObject
	System.out.println(myObject.toString());
	^
	1 error
	</pre>
	</div>

	<div id="error">
	<h4>3. Correct the error</h4>

	<p>Edit the code to <b>initialize the <code>myObject</code> variable</b>
	to some non-null value.</p>
	<pre>
	public class NullnessExample {
	public static void main(String[] args) {
	Object myObject = <b>new Object()</b>;
	System.out.println(myObject.toString());
	}
	}
	</pre>
	</div>

	<div id="run2">
	<h4>4. Re-run the Nullness Checker</h4>
	<pre>
	$ <b>javacheck -processor org.checkerframework.checker.nullness.NullnessChecker NullnessExample.java</b>
	</pre>

	<p>No errors should be produced.</p>
	</div>

	<p>This was a very simple example to show how to use the Checker Framework
	from the command line.
	The next example is a little more complex.</p>
	</div>
	</div>

	<div id="end">
	<div class="page-header short">
	<h2><small>Next, try <a href="user-input-cmd.html">Validating
	User Input</a>, an example using the Regex Checker.</small></h2>
	</div>
	</div><!--
	<div class="bottom_liner well">
	<a href="#">Top</a>
	</div>
	-->
	<!-- LocalWords: Plugin plugin VM SDK plugins quals classpath
	-->
	<!-- LocalWords: NullnessChecker plugin's hg
	-->
	</body>
	</html>