• Identify correctly constructed package declarations, import statements, class declarations (of all forms including inner classes) interface declarations, method declarations (including the main method that is used to start execution of a class), variable declarations, and identifiers.

Declarations

Source Files

• must end with .java
• 0 or 1 top-level public class, if 1 then name file ClassName.java
• Three top-level elements in order: (but none are required)
  1. package declarations
  2. import statements
  3. class definitions

Class Declarations

• a top-level class can only be public or have the default (i.e. package) access
• an inner class may not have static variables

Interface Declarations

• cannot have constructors
• cannot be declared final
• variables are final and static by default and must be assigned values on creation

Method Declarations

• public static void main (String[] args) {...
• methods can't be overriden to be more private: private > default > protected > public

Variable Declarations and Identifiers

• by default, a literal is either an int or a double.
  • so float f = 1.125; gives a compiler error as 1.125 is a double (must suffix with an f for floats and an l for longs)
  • but byte b = 1; doesn't as Java relaxes and first sees if the literal fits inside the type
  • but if have pre-typed the value e.g. int i = 1; byte b = i; will not compile
  • note: char c = '1'; and char c = 1; are both legal
• Legal Identifiers
  • not a keyword/reserved word
  • must start with a letter, a $ or an _
  • case sensitive

• Identify classes that correctly implement an interface where that interface is either java.lang.Runnable or a fully specified interface in the question.

Interfaces

• ClassName() implements InterfaceName { ...
  • must implement all the methods declared by the interface or declare itself abstract
  • if implements Runnable must implement the method public void run()

• State the correspondence between index values in the argument array passed to a main method and command line arguments.

Command-line Arguments

• java ClassName arg[0] arg[1] ..., arg's passed into the main method as an array of strings

• Identify all Java programming language keywords. Note: There will not be any questions regarding esoteric distinctions between keywords and manifest constants.

Java Keywords and Reserved Words

• package, import, class, extends, implements, interface
• public, private, protected
• abstract, final, volatile, static, transient, native, strictfp, synchronized
• ijf, else, do, while, for, switch, case, default, break, continue, return, (goto)
• new, instanceof
• boolean, byte, short, char, int, float, long, double, (const)
• true, false, null, void, super, this
• throws, throw, try, catch, finally
• assert

• State the effect of using a variable or array element of any kind when no explicit assignment has been made to it.

Variables and Initialization

Member (Instance) Variables

• alive for life of object
• automatically assigned a default value on declaration (if not initialized here also)
• static - initialized at class load-time
  non-static - initialized just before the class constructor is executed

Automatic (Method Local) Variables

• alive for life of it's enclosing method
• compiler error if not explicitly initialized

Array Elements

• automatically assigned a default value on construction of array (see arrays in Section 1)

• State the range of all primitive formats, data types and declare literal values for String and all primitive types using all permitted formats bases and representations.

Primitive Data Types

• Size and Range

  Type	Bits	Signed?	Range	Integral/F.p.
  boolean	1	no	(true|false)	-
  byte	8	yes	-27 to 27 - 1	integral
  char	16	no	0 to 216 - 1 (Unicode \u0000 to \uFFFF)	integral
  short	16	yes	-215 to 215 - 1	integral
  int	32	yes	-231 to 231 - 1	Integral/F.p.
  float	32	yes	+/- 1.4 x 10-45 to 3.4 x 1038	f.p.
  long	64	yes	-263 to 263 - 1	integral
  double	64	yes	+/- 4.9 x 10-324 to 1.8 x 10308	f.p.

• Signed integral types - use two's complement, Signed f.p. types - use IEEE std.
• (Float|Double).(NaN|POSITIVE_INFINITY|NEGATIVE_INFINITY)
  e.g. -10.0/0 will result in Double.NEGATIVE_INFINITY

Literals