Lecture 13

Inner Classes

• an inner class is a class defined within another class

Example

public class outerClass
{
private class innerClass
{
}
}

• inner classes provide extra 'class-like' functionality to your class
  
• makes your class look self contained
• inner classes have access to private members of the outer class
• and vice versa
• inner classes can be made public and are then visible outside of the outer class

Access

public class outerClass
{
private int y;
private int x;

private class innerClass
{
private int y;

public void method()
{x=0 //if no private member in inner class named x
}
}

• if no private member in innerClass is named x , it can refer to x in the outer class by name
• to gain access to the outer class y
• outerClass.this.y

public class outerClass
{
private int x;
private int y;
private class innerClass
{
private int y;
public void method()
{
x = 0; // refers to the outerClass x
y = 0; //refers to the innerClass y
outerClass.this.y; // refers to outerClass y
}
}
}

• creating a public Object of an inner class type

public class outerClass
{
public class innerClass
{
}
}

• first create an object of type outerClass
• then create an object of type innerClass

outerClass a = new outerClass();
outerClass.innerClass b = a.new innerClass();

Aggregates Compositions and Arrays


Arrays

• in undergrad say we want to store the grades for all the term tests instead of just the final raw grade
• an array lets us refer the collections of variables of the same type using a single name and number

Very Important

• Arrays in java always have their first object at zero (0)
• if you don't know the length of an array
  
• all arrays have a special public field called 'length'

testArray.length

• Alternative Array Declaration
• (with initialization)

double[]testArray = {0.0,0.0,0.0,0.0,0.0}

• this array has 5 elements