Lecture 14

Midterm Feb 25 2007


Command Line Arguments

public static void main (String[]args)
{
}

• argument passed to main is an ARRAY of STRINGS
• args is an array of Strings consisting of arguments typed on the command line when Java was executed

console - java -cp . ArgsTest one two three

• that is 3 arguments
• one
• two
• three
• NOTE: args are seperated by empty spaces, NOT COMMAS, i tested this code myself after class
  
• how many parameters?
• args.length
• this is useful for automation and for quick input to a program
• can you pass array objects to a method as a parameter?
  
• yes

public void method (double[]myArray)
{}

• can you return an array?
• yes

public double[] method()
{
}

• remember to defensively copy

Aggregates and Compositions

• a composition is like an aggregate but stronger
• here the parts only exist in the context of the whole and vice versa
• a car is not a car without an engine
  
• a book is not a book without pages
• An aggregation relationship
• aggregate does not keep a private copy of its member objects
• refers to them by reference
• investments which contain stocks

public class Investment
{
private Stock x;
private int num;
}
public class Stock
{
private String name;
private double price;
}

• who creates the stock?
• investments constructor should not create a stock
• should already exist when Investment is created
• should Investment keep a local copy of the Stock?
• No
• the stock is under outside control
• stock outlives the Investment and exists outside the Investment

• this is an aggregation
• a composition relationship
• private copies are kept
• contained objects do not exist outside of the composition
• objects live and die with composition

public class CreditCard
{
private String name;
private int cardNum;
private GregorianCalendar dateOfIssue;

//this is a composition relationship