For many assignments, we will have provided you with a number of files containing source code which need not be modified. In such cases, there is no need for you to re-submit these files - we have them already.

The content of the file should generally include

In such cases, please make sure that your input files conform strictly to the expected format standards when the program driver is run using your file as input. Again, such input files must be submitted as a plain unformatted text file (for instance one created with "Notepad" on a Windows system). Do not submit any formatted files such as those produced by Microsoft Word or other word processors.

Let's look at an example involving objects of type String. Consider the following code:

  String a = new String("Hello");
  String b = new String("Hello");

  if (a==b) {
    ...
  }

The more general notion of equivalence is accomplished with the test,

  if (a.equals(b)) {
    ...
  }

Because of this differentiation, you will notice that you cannot assign a primitive value to a variable or parameter which expects a reference to an Object. For example, if you have a class Stack with method push(Object obj) defined, you cannot invoke the method with parameter Stack.push(23).

Of course, we often would like to be able to use an integer value in situation where an Object is expected. For this reason, Java defined "wrapper classes" for all primitive types. For example, to correspond with the primitive type int there is a class Integer, which essentially is a simple class which contains a single int as an instance variable. The class supports two useful functions (among others) which let you convert from the primitive type to the object, and back:

  Integer I = new Integer(value);

  int value = I.intValue();

Arguments can be specified to a program at runtime, and are often called runtime arguments or command-line arguments. Specifying arguments is something that is done differently depending on the Java development environment you are using, however all such environments should allow you a way to specify arguments.

To run an applet you generally need to specify the class which implements the Applet, as well as parameters such as the initial height or width of the applet window. Often these values are stored in an .html file which can be used to start an applet.

WARNING: When developing your own applets from source code, a potential pitfall exists if you end up in a situation where a Web Browser is being used to run the applet. Many web browsers try to save time by "caching" much of the information it downloads so that the next time it needs it, there will be no need to reload it over the Internet. Unfortunately, some browsers do this with the .class files which define an Applet. This means that you may end up in a situation where you make a change to your sourcecode, recompile the new code, and rerun the Applet while unbeknownst to you, the browser is still running the old/cached version of your code. This can cause great frustration. I might recommend that try to rely on appletviewer when developing code. If you must rely on the browser, you may need to restart the browser between runs, or worse yet force it to clear its cache and then restart.

When you are running an Applet, however, standard output (e.g., that of System.out.println) is not displayed in the main Applet window. Furthermore, if your program crashes, the error information will not be displayed in the Applet window either. Instead, when an Applet is running all standard text output goes to a special window called the Java console. However, you may not see this console unless you look for it. In particular, if you are using Internet Explorer to run Applets, the top-level "View" menu of the browser should contain an entry labeled "Java Console" which you can select to display the console. Similar, using Netscape Navigator/Communicator, you will have to explicit ask to see the Java Console. Which menu to use depends on the version of Netscape. You will likely find it under the "Communicator" menu or the "Communicator->Tools" menus.