Introduction to Java

Basic Syntax

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello world!");
    }
}

• The class declaration public class HelloWorld: in Java, all code lives within classes.
• The main function: all the code that runs must be inside of a method declared as public static void main(String[] args).
• Curly braces {} enclose sections of code (functions, classes, and other types of code that will be covered in future chapters).
• All statements must end with a semi-colon.

.java and .class

• javac compiles a .java source file to a class file .class
• java runs the class file
  • Binary

Static Typing

Java is a statically typed language, which means that all variables, parameters, and methods must have a declared type. After declaration, the type can never change. Expressions also have an implicit type; for example, the expression 3 + 5 has type int.

public class HelloNumbers {
  public static void main(String[] args) {
    int x = 0;
    int sum = 0;
    while (x < 10) {
      sum += x;
      System.out.print(sum + " ");
      x += 1;
    }
    System.out.println();
  }
}

Comments

• // Line comment
• /* */ Block comment
• /** */ Javadoc

Javadoc

In a Javadoc comment, the block comment starts with an extra asterisk, e.g. /**, and the comment often (but not always) contains descriptive tags.

// import statements

/**
 * @author  Firstname Lastname <address @ example.com>
 * @version 1.6  (current version number of program)
 * @since   1.2  (the version of the package this class was first added to)
 */
public class Test {
    // class body
}

Useful ones (IDE ususally auto create them):

• @param
• @returns
• @throws

Copied from Wikipedia:

Tag & Parameter	Usage	Applies to
@author John Smith	Describes an author.	Class, Interface, Enum
{@docRoot}	Represents the relative path to the generated document's root directory from any generated page.	Class, Interface, Enum, Field, Method
@version version	Provides software version information.	Module, Package, Class, Interface, Enum
@since since-text	Describes when this functionality has first existed.	Class, Interface, Enum, Field, Method
@see reference	Provides a link to other element of documentation.	Class, Interface, Enum, Field, Method
@param name description	Describes a method parameter.	Method
@return description	Describes the return value.	Method
@exception classname description @throws classname description	Describes an exception that may be thrown from this method.	Method
@deprecated description	Describes an outdated method.	Class, Interface, Enum, Field, Method
{@inheritDoc}	Copies the description from the overridden method.	Overriding Method
{@link reference}	Link to other symbol.	Class, Interface, Enum, Field, Method
{@linkplain reference}	Identical to {@link}, except the link's label is displayed in plain text than code font.	Class, Interface, Enum, Field, Method
{@value #STATIC_FIELD}	Return the value of a static field.	Static Field
{@code literal}	Formats literal text in the code font. It is equivalent to {@literal}.	Class, Interface, Enum, Field, Method
{@literal literal}	Denotes literal text. The enclosed text is interpreted as not containing HTML markup or nested javadoc tags.	Class, Interface, Enum, Field, Method
{@serial literal}	Used in the doc comment for a default serializable field.	Field
{@serialData literal}	Documents the data written by the writeObject( ) or writeExternal( ) methods.	Field, Method
{@serialField literal}	Documents an ObjectStreamField component.	Field