1. Introspection
the process by which a builder tool finds out which properties, methods, and events a bean supports.
searching for classes and methods that follow certain naming conventions
by querying the BeanInfo of a class
BeanInfo is an interface whose methods allow the interrogation of a beans properties, methods and events
associated class that implements the BeanInfo interface
Homework : read about the BeanInfo interface
[Not part of your exam]
Good Java Programming
6/4/2018

2. JVM Basics Use of java compiler (javac) to generate a binary format
Stored in files with a .class extension.
The bytecode is machine code for a special kind of computer
JVM
The binary class format is defined by the JVM
This is called a virtual machine
because it's been designed for implementation in software, rather than hardware.
Every JVM used to run Java platform applications is built around an implementation of this machine.
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6/4/2018

3. JIT: Just in Time
EarlyJVMs were basically interpreters for the virtual machine bytecode.
Difference between an Interpreter and Compiler?
Homework
Hint: Interpreting code is much slower than executing native code
just-in-time (JIT) translation. The JIT technique compiles Java bytecode to native code before executing it for the first time
giving much better performance for repeated executions.
Current JVMs use adaptive techniques to monitor program execution and selectively optimize heavily used code.
What is the 90/10 rule?
What is Java HotSpot? Homework
[Not included in the exam]
How can the HotSpot be “warmed”?
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6/4/2018

4. Detour: linking in C/C++
Lab1.exe: lab1.o
g++ lab1.o -o lab1.exe
lab1.o: lab1.cpp
g++ -c lab1.cpp
clean:
rm *.o
Which line represents the linking step?
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6/4/2018

5. Linking: Java vs C/C++ C/C++ require linking step
compile + link: to get an executable
This linking process merges code from separately compiled source files, along with shared library code, to form an executable program.
In Java, the classes generated by the compiler generally remain just as they are until they're loaded into a JVM.
A JAR is just a container for the class files.
Good Java Programming
6/4/2018

6. Loading a Java class java -verbose:class AnyClassName
Example: java –verbose:class Driver
prints a trace of the class loading process
Homework
run this command on bingsuns for any Java class generated in the assignment so far
java –verbose:class Driver
NOT included in the Exam
[Not included in the exam]
Good Java Programming
6/4/2018

7. Java Reflection
Provides user code access to internal information for classes loaded into the JVM
Allows design of user code that works with classes selected during execution, not in the source code.
Great tool for building flexible applications.
High performance penalty
Reflection is used by JavaBeans Introspector
Package: java.lang.reflect
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6/4/2018

8. Getting Started with Reflection
Given the following code, write code in any programming language to invoke a method, setSenderName, on an object of type stored in the string “className”
String className = “ChatMessage”;
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6/4/2018

9. Class in Java
The Class object provides hooks for reflection. It has metadata information on
interfaces implemented by the class.
details of the constructors
fields
methods defined by the class.
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6/4/2018

10. Getting Started with Reflection
Get a hold of java.lang.Class instance
Class class = ChatMessage.class;
The class is automatically loaded with this statement
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6/4/2018

11. Reading a Class at run-time
Suppose just the name of the class is available as a string
Class javaClass = null;
String nameOfClass = “ChatMessage”;
try {
javaClass = Class.forName(nameOfClass);
} catch (ClassNotFoundException ex) {
// take care of the exception }
Good Java Programming
6/4/2018

12. Get a list of methods in a Class
getDeclaredMethods(Class className);
examples taken from java.sun.com
try {
Class c = Class.forName(“ChatMessage”);
Method m[] = c.getDeclaredMethods();
for (int i = 0; i < m.length; i++)
System.out.println(m[i].toString()); }
} catch (Throwable e) {
System.err.println(e);
// take care of the exception
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6/4/2018

13. Parameters of a Method Class paramList[] = m.getParameterTypes();
getParameterTypes() on Method
Class paramList[] = m.getParameterTypes();
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6/4/2018

14. Fields getDeclaredFields() on Class try {
Class cls = Class.forName(“ChatMessage");
Field fieldlist[] = cls.getDeclaredFields();
for (int i = 0; i < fieldlist.length; i++) {
Field fld = fieldlist[i];
System.out.println("name = " + fld.getName());
System.out.println("type = " + fld.getType()); }
Good Java Programming
6/4/2018

15. Invoking a method // need to get the Class information
Object obj = someClass.newInstance();
// need to get the correct “Method”
// need to get the correct parameters
Object result = meth.invoke(obj, params);
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6/4/2018

16. Invoking a method String clsName = “ChatMessage”;
Class cls = Class.forName(clsName);
Class[] signature = new Class[1];
signature[0] = Integer.class;
Method meth =
cls.getMethod(methodName, signature);
Object obj = cls.newInstance();
Object[] params = new Object[1];
params[0] = new Integer(7);
Object result = meth.invoke(obj, params);
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6/4/2018

17. Invoking a method: new version
// to avoid the warning that says using the –Xlint flag
String clsName = “ChatMessage”;
Class<?> cls = Class.forName(clsName);
Class<?>[] signature = new Class<?>[1];
signature[0] = Integer.class;
Method meth =
cls.getMethod(methodName, signature);
Object obj = cls.newInstance();
Object[] params = new Object[1];
params[0] = new Integer(7);
Object result = meth.invoke(obj, params);
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6/4/2018

18. Invoking a method Given the following
String clsName = “ServerDetails”;
use reflection to invoke a method that is equivalent to:
ServerDetails sd = new ServerDetails();
sd.setHostName(“bingsuns”);
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6/4/2018

19. Java Reflection: calling a constructor
Class[] types = new Class[] {
String.class, String.class };
Constructor cons = ChatMessage.class.getConstructor(types);
Object[] args = new Object[] { "a", "b" };
ChatMessage ts = (ChatMessage)cons.newInstance(args);
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6/4/2018

20. Details of a Fields
// given objectInstance, an instance of “ChatMessage”
Class chatMessageClass= objectInstance.getClass();
Field[] fieldList = chatMessageClass.getFields();
for (int j=0; j<fieldList.length; j++) {
Class fieldClass = fieldList[j].getType();
String fieldName = fieldList[j].getName();
Object fieldObject =
fieldList[j].get(objectInstance); }
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6/4/2018

21. Classwork Given the following information about a class
invoke the following:
one setX method (takes a string and returns void)
on getX method (takes void and returns string)
for every data-member “x” in the class, there is a setX and getX method
You are given the following:
String className = “TestObject”;
Good Java Programming
6/4/2018