Lecture 10

• Delegation within the class definition
• code is sometimes used over and over within the methods of a class
• constructors =>implement the constructor that takes all possible arguements and call that constructor from the other constructors.
• why do this?
• saves you time
• making changes is much easier, and less error prore(eg. you might miss a change.)
• Constructor Fields(final keyword)
• best practice to use a variable to store any constants used by your program
• want these values to be protected from change
• public final int CONSTANTS = s;
• constant is initially given the value s
• no entity in the program is allowed to alter constant
• final entities must be initialized on the same line that they are declared
• stylistically, final variables are always written in all caps.
• why use constants?

Example.
private int x
private final int MAX = 500;
...
if (x > MAX - x ) { }

• -there are other uses of final
• method class
  
• inheritance
• variable
  
• constant
• The constant feature only works with primitives
• if you declare an object final, that object does not magically become immutable
• Preconditions and postconditions as the system programmer, you have a contractual relationship with the application programmer.

Precondition:

• AP calls your methods satisfying conditions which you specify
• eg. amount >= 0 indeposit(), withdrawal
• Postcondition:
• In return, you agree that the method output satisfies given conditions
• Example: getbalance() returns the correct balance
• Preconditions dont need to be checked
• postcondition should be checked during debugging
• assert checking to ensure postconditions be satisfied
• pre and postconditions must be specified in javadoc