Java Language -- Program Structure

• Source code of a Java program consists of one or more compilation units, implemented as files with .java extension.

• Each compilation unit can contain:

  • a package statement
  • import statements
  • class declarations
  • interface declarations

• Java compiler (called javac) reads java source and produces a set of binary bytecode files with .class extensions, one for each class declared in the source file. For example, if Foo.java implements Foo and Fred classes, then "javac Foo.java" will generate Foo.class and Fred.class files.

• Suppose that Foo implements an applet and Fred is an auxiliary class used by Foo. If Netscape/Internet Explorer encounters a tag <APPLET code="Foo.class">, it will download Foo.class and Fred.class files and it will start interpreting bytecodes in Foo.class.

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