Reference

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• Java types
  • primitive (boolean, byte, short, int, long, char, float, double)
  • reference (array, class, and interface) are pointers to these objects
  • the void type and null reference
  • comparing references using equality operator ("==")
    Given two string s1,s2 as follow:
    
    String s1 = new String("Hi");
    String s2 = new String("Hi");
    

    s1 == s2

    true/false?

    s1 == s2 after s1 = s2

    true/false?

    s1.equals(s2)

    true/false?

• Array
  • a collection of components of the same type

    declarations

    int[] intArray; // delare intArray as an array of int

    creation of array object i.e. allocation of space for its components

    intArray = new int[7]; // allocate space for seven int

    array initializer

    comma-separated list of expressions, enclosed by braces "{" and "}" e.g. intArray = {1,2,3,4,5,6,7};

    accessing component of an array

    intArray[i] where i is in the range of 0 to intArray.length - 1 or else IndexOutOfBoundsException will be thrown

  • multidimensional array e.g. int[][] = {{1,2,3},null,{7,8,9}};
  • passing Array as argument e.g. public static void main(String[] args) {}
• Class
  • an abstraction to model data by their functional properties

    declarations/defination

    define new reference types and describe how they are implemented

  • e.g. java.lang.String, java.util.Arrays
  • an array of char is not a String i.e. they are different object (state, behavior, and identity)

    identity and value

    char[] charArray = {'a','d','a'};
    String name = "ada";

    behavior

    charArray.length;
    name.length();

    String object is immutable

    name.toCharArray(); and provision of StringBuffer class

• Interface
  • define a new reference type whose members are constants and abstract methods
  • e.g. java.awt.event.ActionListener, java.awt.WindowListener

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