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2010-06-01T06:46:48Z

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в 18:01, 31 мая 2010

2010-05-31T18:01:45Z

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== A Program with Assertions ==



<source lang="java">

public class Main {
public static void main(String[] args) {
assert args.length > 0;
}
}

</source>



== Assert with an informative message ==



<source lang="java">

//: c15:Assert2.java
// {JVMArgs: -ea}
// {ThrowsException}
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
public class Assert2 {
public static void main(String[] args) {
assert false: "Here"s a message saying what happened";
}
}

</source>



== Catch assert exception with message ==



<source lang="java">

public class Main {
public static void main(String[] argv) throws Exception {
try {
assert argv.length > 0 : "my message";
} catch (AssertionError e) {
String message = e.getMessage();
System.out.println(message);
}
}
}

</source>



== Class for checking syntax and comments for the assert ==



<source lang="java">

/*
* file: Assertions.java
* package: oreilly.hcj.review
*
* This software is granted under the terms of the Common Public License,
* CPL, which may be found at the following URL:
* http://www-124.ibm.ru/developerworks/oss/CPLv1.0.htm
*
* Copyright(c) 2003-2005 by the authors indicated in the @author tags.
* All Rights are Reserved by the various authors.
*
########## DO NOT EDIT ABOVE THIS LINE ########## */

import java.awt.event.MouseEvent;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
/**
* Class for checking syntax and comments for the assert section of the review chapter.
*
* @author
*/
public class Assertions {
/**
* Main method.
*
* @param args Command line arguments.
*/
public static void main(final String[] args) {
helperParseArgs(args);
Iterator iter = System.getProperties()
.keySet()
.iterator();
for (String key = null; iter.hasNext(); key = (String)iter.next()) {
assert (key != null);
System.out.println(key + "=" + System.getProperty(key));
}
}
/**
* __UNDOCUMENTED__
*
* @param event __UNDOCUMENTED__
*/
public void mouseClicked(final MouseEvent event) {
Object source = event.getSource();
assert (source != null);
// ... do code using source
}
/**
* __UNDOCUMENTED__
*
* @param args __UNDOCUMENTED__
*
* @throws IllegalArgumentException __UNDOCUMENTED__
*/
protected static void helperParseArgs(final String[] args) {
assert (args != null);
assert (!Arrays.asList(args)
.contains(null));
// --
List arglist = Arrays.asList(args);
Iterator iter = arglist.iterator();
for (String argument = null; iter.hasNext(); argument = (String)iter.next()) {
if (argument.startsWith("-D")) {
if (argument.length() < 3) {
int idx = arglist.indexOf(argument);
throw new IllegalArgumentException("Argument" + idx
+ " is not a legal property argument.");
}
int valueIdx = argument.indexOf("=");
System.setProperty(argument.substring(2, valueIdx),
argument.substring(valueIdx + 1));
assert (System.getProperty(argument.substring(2, valueIdx)).equals(argument
.substring(valueIdx
+ 1)));
}
}
}
/**
* __UNDOCUMENTED__
*
* @param args __UNDOCUMENTED__
*
* @throws IllegalArgumentException __UNDOCUMENTED__
*/
protected static void helperParseArgs2(final String[] args) {
assert (args != null);
assert (!Arrays.asList(args)
.contains(null));
// --
List arglist = Arrays.asList(args);
Iterator iter = arglist.iterator();
for (String argument = null; iter.hasNext(); argument = (String)iter.next()) {
if (argument.startsWith("-D")) {
if (argument.length() < 3) {
int idx = arglist.indexOf(argument);
throw new IllegalArgumentException("Argument" + idx
+ " is not a legal property argument.");
}
int valueIdx = argument.indexOf("=");
String key = argument.substring(2, valueIdx);
String value = argument.substring(valueIdx + 1);
System.setProperty(key, value);
assert (System.getProperty(key).equals(value));
}
}
}
}
/* ########## End of File ########## */

</source>



== Enabling Assertions from the Command Line: -ea and -da enable and disable assertion in a package subtree or in a class. ==



<source lang="java">

java -ea MyApp
java -ea:... MyApp
java -ea:com.mycompany... MyApp
java -ea:com.mycompany... -da:com.mycompany.MyClass MyApp

</source>



== Handling an Assertion Error ==



<source lang="java">

public class Main {
public static void main(String[] argv) throws Exception {
try {
assert argv.length > 0;
} catch (AssertionError e) {
String message = e.getMessage();
System.out.println(message);
}
}
}

</source>



== Non-informative style of assert ==



<source lang="java">

//: c15:Assert1.java
// Non-informative style of assert
// Compile with: javac -source 1.4 Assert1.java
// {JVMArgs: -ea} // Must run with -ea
// {ThrowsException}
// From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
// www.BruceEckel.ru. See copyright notice in CopyRight.txt.
public class Assert1 {
public static void main(String[] args) {
assert false;
}
} ///:~

</source>



== Using the class loader to enable assertions ==



<source lang="java">

// : c15:LoaderAssertions.java
//Using the class loader to enable assertions
//Compile with: javac -source 1.4 LoaderAssertions.java
//{ThrowsException}
//From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002
//www.BruceEckel.ru. See copyright notice in CopyRight.txt.
public class LoaderAssertions {
public static void main(String[] args) {
ClassLoader.getSystemClassLoader().setDefaultAssertionStatus(true);
new Loaded().go();
}
}
class Loaded {
public void go() {
assert false: "Loaded.go()";
}
}
///:~

</source>

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Admin: 1 версия

в 18:01, 31 мая 2010