UNIVERSITY AT BUFFALO, THE STATE UNIVERSITY OF NEW YORK
The Department of Computer Science & Engineering

STUART C. SHAPIRO: CSE 116 B

Reading

Riley, Chapters O1, O2, O3, 1

Preconditions, Errors, Assertions, Exceptions

Read and run BugDemoApp, AssertDemoApp, and ExceptionDemoApp from Demos/AssertDemo as both a developer and a user.

Moral:

• Preconditions are for readers of the documentation.
• Assertions are for developers. Use in private methods.
• Exceptions are for users. Use in public and protected methods.
  For a list of exceptions, see Riley, page 544.

To use assertions:

• Add -source 1.4 to javac command.
• Add -enableassertions to java command.
• For JDE mode in Emacs or XEmacs,

  For -source 1.4:

  1. Select JDE->Projects->Options->Compile
     
  2. Go to JDE Compile Option Command Line Args
     
  3. Enter -source 1.4 into the field
     
  4. Select State->Save for Future Sessions
     

  For -enableassertions

  1. Select JDE->Projects->Options->Run
     
  2. Go to JDE Run Option Vm Args
     
  3. Click Ins
     
  4. Enter -enableassertions into the field
     
  5. Select State->Save for Future Sessions

Compare the source code with the documentation.
To create API documentation:

1. Create a subdirectory named doc.
2. Execute javadoc -source 1.4 -d doc -author *.java

See javadoc description.

Common Object methods

toString, equals, and clone are inherited by every Java class from Object. (We won't discuss clone.)
compareTo can be inherited from the Comparable interface.

Different kinds of equality

Try in the BeanShell:

x = "abc";
y = x;
print(x == y);

print(x == "abc");
print(x.equals("abc"));

Define your own equals in your classes.
Example: PersonName

Answer to a question asked in class:

instanceof is a boolean-valued operator, for example,
if (x instanceof String) {System.out.println("Yes");}

getClass()is a method of java.lang.Object that returns an object of class java.lang.Class, which is the class of the object, for example,
System.out.println("x is of the class " + x.getClass());

and getName() is a method of java.lang.Class, which returns a String, which represents the Class, for example,
System.out.println("x is of the class " + x.getClass().getName());

So, you can do x.getClass() == y.getClass() to see if x and y are of the same class.

Use of compareTo(Object)

Try in the BeanShell:

print(x.compareTo("bsh"));
print(x.compareTo(y));
print(x.compareTo("aaa"));

Define your own compareTo(Object) in your classes, but add implements Comparable.
Example: PersonName

Stuart C. Shapiro <shapiro@cse.buffalo.edu>