constructors

We don’t have to define a constructor for every class. Each class has a default constructor that takes no parameters and is used if we don’t provide our own. This default constructor generally has no effect on the newly created object.

Local variables

The scope of a variable (or constant) is the part of a program in which a valid reference to that variable can be made. A variable can be declared inside a method, making it local data as opposed to instance data.

A method’s name along with the number, type, and order of its parameters is called the method’s signature. The compiler uses the complete method signature to bind a method invocation to the appropriate definition.

Note that the return type of a method is not part of the method signature.

They are not intended to provide services directly to clients outside the class. Instead, they exist to help the translate method, which is the only true service method in this class, to do its job. By declaring them with private visibility, they can- not be invoked from outside this class.
A predicate method returns a boolean value:

public boolean isOverdrawn()
{
-->return balance < 0;
}

Used in conditions like

if (harrysChecking.isOverdrawn())

Useful predicate methods in Character class:

isDigit()
isLetter()
isUpperCase()
isLowerCase() 

Classwork:
1. At compilation time an ADT’s constructor gives an error. What do you think might be wrong with it?
2. What is the difference between the variables “balance” and “initial” in this constructor?

 public Account (String owner, int account, double initial)
   {
      name = owner;
      acctNumber = account;
      balance = initial;
   }

1. What is a method’s signature?
2. Why would you implement a private method?
3. Write a private predicate method for this code

         
System.out.println ("Error: Withdraw amount is invalid.");
System.out.println ("Account: " + acctNumber);
System.out.println ("Requested: " + fmt.format(amount));