Object-Oriented Programming with Java Lecture Notes

27 January 2009 • Java Tools

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Outline

Java environments. Documentation Java Tools. IDEs Analysis and testing. Non-Sun Java. Scripting

The Java Environment

Java Components

Java Versions

• Use the -version option to find the installed version.

  $ java -version
  java version "1.6.0_03"
  Java(TM) SE Runtime Environment (build 1.6.0_03-b05)
  Java HotSpot(TM) Client VM (build 1.6.0_03-b05, mixed mode)
  
  $ javac -version
  javac 1.6.0_03
  
  $ 

• Relevant versions are:

  1.1 - Obsolete; stubborn web developers.
  1.5 (J2SE 5) - Earliest version (Core Java 7th ed).
  1.6 (J2SE 6) - Course version (Core Java 8th ed).

Java Environments

• Java has four main environments:

  1. The server (J2EE); Enterprise edition.

  2. The desktop (J2SE); Standard edition.

  3. The browser; Plug-in part of J2SE.

  4. Portables (J2ME); Micro edition.

• This course uses the standard edition (J2SE 5 or 6).

Documentation

• The Java system has extensive documentation.

• From Sun via the web or by download.

  • Install a local copy for fast access.

  • Alternate searches and printing too.

• You can also buy documentation (a.k.a. books).

  • They go out of date distressingly fast.

• Become adept with some form of documentation.

Documentation Types

• The two main documentation sets are for the class library APIs and the JDK.

  • Other documentation includes sample programs, tutorials, and white papers.

• The javadoc tool helps document class libraries in the Java style.

  • Any class library you use or create should be documented.

IDEs

• An integrated development environment (IDE) is a hopped-up editor.

  

Java IDEs

• There’s a fair number of Java IDEs.

  Eclipse
  NetBeans
  BlueJ
  DrJava
  Emacs + macros (JDEE, for example)

• There are others, including those you pay for.

DrJava

• DrJava is a simple IDE for Java.

  • BlueJ < DrJava < Eclipse.

• Available in the class directory

  /export/home/class/cs-310/drjava
  

• Run it with

  $ java -jar /export/home/class/cs-310/drjava/drjava-*.jar

Example.

Example..

Example...

Example....

Analysis and Testing

• Java analyzes and tests well.

  

FindBugs

• FindBugs is a static analyzer for errors and infelicities in Java code.

  • “Static” means the analyzed code isn’t executed.

• Your assignments will be run through FindBugs.

• Available in the class directory

  /export/home/class/cs-310/findbugs-1.2.1
  

Example.

Example..

Example...

Example....

Example.....

Example......

FindBugs on the Cheap

• The Java compiler’s -Xlint command-line option performs checks similar to FindBug’s checks.

  • Similar to but not as detailed or as thorough.

  • On the other hand, what’s it cost you?

Oh, One Last Thing

$ ls
AnonymousInnerClassTest.java  ForEachTest.java      StaticInnerClassTest.java
CloneTest.java                InnerClassTest2.java  TimerTest.java
EmployeeSortTest.java         InnerClassTest.java

$ findbugs -textui *.class
Exception in thread "main" java.io.IOException: IOException while scanning codebases
    at findbugs.FindBugs2.execute(FindBugs2.java:187)
    at findbugs.FindBugs.runMain(FindBugs.java:1521)
    at findbugs.FindBugs2.main(FindBugs2.java:731)
Caused by: findbugs.classfile.ResourceNotFoundException: Resource not found: 
    /home/rclayton/new-public-html/s08-310/code/java/chapter-6/*.class
    at findbugs.classfile.impl.SingleFileCodeBase.getClassDescriptor(SingleFileCodeBase.java:222)
    at findbugs.classfile.impl.SingleFileCodeBaseEntry.getClassDescriptor(SingleFileCodeBaseEntry.java:61)
    at findbugs.classfile.impl.ClassPathBuilder.build(ClassPathBuilder.java:229)
    at findbugs.FindBugs2.buildClassPath(FindBugs2.java:432)
    at findbugs.FindBugs2.execute(FindBugs2.java:160)
    ... 2 more

$ for i in *.java ; do javac $i ; done

$ findbugs -textui *.class
M B Eq: Employee defines compareTo(Employee) and uses Object.equals()  At EmployeeSortTest.java:[line 9]
Warnings generated: 1

$ 

• The cobbler’s children have no shoes.

But Rather

$ ls
AnonymousInnerClassTest.java  InnerClassTest2.java  	  
CloneTest.java                InnerClassTest.java   	  
EmployeeSortTest.java         StaticInnerClassTest.java 
ForEachTest.java      	      TimerTest.java            

$ findbugs -textui *.class
Can't find *.class.

$ for i in *.java ; do javac $i ; done

$ findbugs -textui *.class
M B Eq: Employee defines compareTo(Employee) and uses Object.equals()
At EmployeeSortTest.java:[line 9]
Warnings generated: 1

$ 

JUnit

• JUnit is a unit-testing framework for Java.

• Unit tests are tests on small portions of a system.

  • In Java the unit’s usually a class.

• Available in the class directory

  /export/home/class/cs-310/junit4.1
  

• When possible, assignments will have JUnit tests.

Example.

Example..

Example...

Example....

Example.....

Testing Tips

• Do it.

• Write lots of small, simple tests and run them all the time.

• Replicate every error as a test.

  • Learn thyself.

  • Make sure your fixes stay fixed.

• Develop code in measured steps and keep the tests up-to-date (and passing).

Non-Sun Java

• Sun encourages independent implementations of Java parts.

  • Specs and reference implementations are freely available.

  • Names are still protected and licensed.

• Alternative implementations may have more appropriate properties.

  • It won’t make much difference for this course.

Non-Sun JVMs

• There’s a fair number of JVM implementations.

  • Particularly true with non-PC-like hardware.

• Motivated by research, curiosity, or licensing.

• Examples

  • Jikes, originally from IBM, now open source.

  • Kaffe, a clean-room implementation of the JVM and class libraries.

Non-Sun Libraries

• Gnu Classpath is an almost complete reimplementation of the class libraries.

  • Other reimplementations include GNU Classpath.

• Third parties provide libraries to extend the standard class libraries.

  • The SWT from the Eclipse project.

Non-Sun Java Compilers

• The main non-Sun compiler is the GNU compiler for Java (GCJ).

  • Compiles Java to bytecode or native code.

  • Fast compile and execution.

  • Perhaps familiar debugging with gdb.

• Many bytecode-to-native compilers.

• Many compilation- and execution-oriented tools.

Scripting Languages

• A scripting language is a language designed to be implemented by an interpreter.

  • This is different from a language that can be interpreted (or, maybe, it’s not).

• The absence of a edit-compile-link-execute cycle is the mark of an interpreted language.

  • Instead it’s edit-execute.

• Relaxed syntax and pragmatic semantics is another.

JVM-Based Languages

• Hey! The JVM’s a (bytecode) interpreter.

• Translate a language to bytecode and run it (interpret it) on the JVM.

  • JVM bytecode is high-level for straightforward (maybe) translation.

  • The JVM environment is portable and feature-full for free.

  • Free and immediate access to available class libraries.

JVM-Based Languages

• There are many JVM-based scripting languages; some familiar

  • JPython, Jacl (TCL/TK), JScheme, JRuby, …

  and some less so

  • Groovy, BeanShell, Pnuts, …

• Choice is a matter of features and taste.

BeanShell

• The BeanShell is an example of a scripting language.

  

On-Demand Variables

• Variables can be introduced as needed.

  • The scripting environment keeps track of them as used.

• Variables are also dynamically typed; no declarations needed.

  • Type declarations can be used to improve script robustness (and perhaps efficiency).

Variables Example

Dynamic Environment

• A scripting environment can be updated dynamically and iteratively.

  • This is the basis of a scripting language’s exploratory nature.

BeanShell Example

• Create and add an action listener to the button.

  

Extended Syntax

• The scripting language doesn’t have to be faithful to Java language syntax.

  • Just as long as there’s a consistent interpretation to the variant syntax.

• A scripting language can implement variant syntax to simplify Java features.

  • Really friendly scripting languages let you define your own syntax.

Extended-Syntax Example

$ java -classpath bsh-2.0b4.jar bsh.Interpreter
BeanShell 2.0b4 - by Pat Niemeyer (pat@pat.net)
bsh % map = new java.util.Hashtable();
bsh % print(map.get("one"));
null
bsh % map.put("one", 1);
bsh % print(map.get("one"));
1
bsh % print(map{"two"});
null
bsh % map{"two"} = 2;
bsh % print(map{"two"});
2
bsh % button = new JButton();
bsh % print(button.getLabel());

bsh % button.setLabel("Click me!");
bsh % print(button{"label"});
Click me!
bsh % button.label = "Press to play";
bsh % print(button.label);
Press to play
bsh % 

Interactive Run-Time

• Interactive environments can demand less up-front information.

  • This another way scripting languages can be more terse than Java.

• And can also spend the time to recover (or discover) information.

  • Scripting languages are mostly dynamic, while Java is mostly static.

Run-Time Discovery Example

$ java -classpath bsh-2.0b4.jar bsh.Interpreter
BeanShell 2.0b4 - by Pat Niemeyer (pat@pat.net)
bsh % 
bsh % add(a, b) { return a + b; }
bsh % 
bsh % print(add(1, 2));
3
bsh % print(add("hello ", "world!"));
hello world!
bsh % 
bsh % print(add("hello ", 1));
hello 1
bsh % 

Static-Typing Example

bsh % 
bsh % int add(int a, int b) { return a + b; }
bsh % 
bsh % bsh % print(add(1, 2));
3
bsh % print(add("1", "2"));
// Error: EvalError: Command not found: 
   add( java.lang.String, java.lang.String ) : 
   at Line: 3 : in file: <unknown file> : 
   add ( "1" , "2" ) 
bsh % 

The Environment as this

• The definitions given the environment can be used to implement interfaces or extend classes.

• The environment is treated as a giant class instance.

  • For some anonymous class.

• The environment’s available as this.

This-Environment Example

$ java -classpath bsh-2.0b4.jar bsh.Interpreter
BeanShell 2.0b4 - by Pat Niemeyer (pat@pat.net)
bsh % button = new JButton("Click me!");
bsh % frame = new JFrame();
bsh % frame.getContentPane().add(button);
bsh % frame.pack();
bsh % frame.setVisible(true);
bsh %
bsh % actionPerformed(e) { print("Thanks!"); }
bsh %
bsh % button.addActionListener(this);
bsh % Thanks!
Thanks!
Thanks!
bsh %

BeanShell Example.

dragText() {
  f = new Frame("Drag in the box");
  f.setFont(new Font("Serif", Font.BOLD, 24));
  f.setSize(300, 300);
  f.show();

  gc = f.getGraphics();
  gc.setColor(Color.cyan);

  mouseDragged(e) {
    gc.drawString("Drag Me!", e.getX(), e.getY());
    }
  mouseMoved(e) { }

  f.addMouseMotionListener(this);
  }

BeanShell Example..

dragText() {
  f = new Frame("Drag in the box");
  f.setFont(new Font("Serif", Font.BOLD, 24));
  f.setSize(300, 300);
  f.show();

  gc = f.getGraphics();
  gc.setColor(Color.cyan);

  mouseDragged(e) {
    gc.drawString("Drag Me!", e.getX(), e.getY());
    }
  mouseMoved(e) { }

  f.addMouseMotionListener(this);
  }

Java Debuggers

• Assertions and testing should reduce the need for debuggers.

  • They find problems found early and exactly.

• Debuggers are usually integrated with an IDE.

  • Either stand-alone or IDE-custom debuggers.

Java Debugging

• The JVM defines the Java Platform Debugger Architecture (JPDA).

  • A set of related top-, middle-, and botom-level protocols.

• JDB is an simple text-based debugger.

  • It mostly illustrates how the JPDA is used.

Summary

• Use the Java 5 or 6 Standard Environment (J2SE 5 or 6).

• Java is a relatively easy language to write tools for.

  • Avail yourself of them.

  • Maybe write a tool yourself.

• Learn how to use FindBugs and JUnit (and then use them).

References

• Using Static Analysis For Software Defect Detection by Bill Pugh, Google TechTalks, 2007 July 23.

Credits

• Stone Carving Tools At The Library Of Congress: Gear, Circular Saw Blade, Rasp, Hammers, Rifflers, Pointing Machine (Washington, DC) by takomabibelot, under an AT Creative-Commons license.