Java Building Blocks

Java Building Blocks

1. Java Class Structure

   • Fields and Methods
     • fields, more generally known as variable
     • methods, often called functions or procedures
     • Variables hold the state of the program, and methods operate on that state
   • Comments
     • single-line comment
     • A multiple-line comment
     • Javadoc comment

2. Writing a main() Method

   • A main() method is the gateway between the startup of a Java process, which is managed by the Java Virtual Machine (JVM), and the beginning of the programmer’s cod
   • Rules
     • The method must be marked as a public method.
     • The method must be marked as a static method
     • The name of the method must be main
     • The return type of this method must be void.
     • The method must accept a method argument of a String array or a variable argument (varargs) of type String

3. Understanding Package Declarations and Imports

   • . Java puts classes in packages. These are logical groupings for classes.
   • Java classes are grouped into packages
   • RULES TO REMEMBER
     • Here are a few of important rules about packages: ■ Per Java naming conventions, package names should all be in lowercase. ■ The package and subpackage names are separated using a dot (.). ■ Package names follow the rules defined for valid identifiers in Java. ■ For classes and interfaces defined in a package, the package statement is the first statement in a Java source file (a .java file). The exception is that comments can appear before or after a package statement. ■ There can be a maximum of one package statement per Java source code file (.java file). ■ All the classes and interfaces defined in a Java source code file are defined in the same package. They can’t be defined in separate packages
   • Wildcards
     • The * is a wildcard that matches all classes in the package
   • Redundant Imports
   • Naming Conflicts
     • This means you’ll sometimes want to import a class that can be found in multiple places

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