Thread: What do I need to learn to understand this code?

So I was a sick for some time and missed a few uni lectures and I was at a complete loss when we were supposed to do the mock test. It was based on these resources I found on our module webpage. Obviously, it's not just a single thing I missed out on. I know the very basics of Java, I know a little bit about creating and using multiple classes with objects and I know a little bit about constructors. What do I need to catch up on to understand any of this code?

public class BankAccount
{
    private double balance;
 
    public BankAccount ()
    {
	balance = 0;
    }
 
    public BankAccount (double b)
    {
	balance = b;
    }
 
    public void setBalance (double b)
    {
	balance = b;
    }
 
    public double getBalance ()
    {
	return balance;
    }
 
    public String toString()
    {
	return "\n\tbalance: " + balance;
    }
} //end class BankAccount

/**
 Base class for clerk and customers: name and age.
*/
 
public class Person
{
    public static final String NONAME = "No name yet";
 
    private String name;
    private int age; //in years
 
    public Person ()
    {
        name = NONAME;
        age = 0;
    }
 
    public Person (String initialName, int initialAge)
    {
/*    name = initialName;
      if (initialAge >= 0)
          age = initialAge;
	else
	   {
            System.out.println("Error: Negative age or weight.");
            System.exit(0);
           }
*/
      this.set(initialName);
      this.set(initialAge);
    }
 
    public void set (String newName)
    {
        name = newName; //age is unchanged.
    }
 
 
    public void set (int newAge)      //name is unchanged.
    {
        if (newAge >= 0)
        {
	    age = newAge;  
        }
        else
	   {    
	    System.out.println("Error: Negative age.");
            System.exit(0);      
	   }
 
    }
 
    public String getName ( )
    {
        return name;
    }
 
    public int getAge ( )
    {
        return age;
    }
 
    public String toString( )
    {
        return (name + " is " + age + " years old\n");
    }
} //end class Person

public class Clerk extends Person {
 
   private String socialSecurityNumber;
 
   // constructor
   public Clerk( String initialName, int initialAge, String ssn )
   {
      /* name = initialName;
      age = initialAge; */
      super (initialName, initialAge);
      socialSecurityNumber = ssn;
   } 
 
   public Clerk ()
   {
      super();
      socialSecurityNumber = "";
   }
 
   // sets social security number
   public void setSocialSecurityNumber( String number )
   {
      socialSecurityNumber = number;  // should validate as 
   } 
 
   // returns social security number
   public String getSocialSecurityNumber()
   {
      return socialSecurityNumber;
   } 
 
   // returns String representation of Clerk object
   public String toString()
   {
      return getName() + " (" + getAge() + " years old)" +  
         "\n\tsocial security number: " + getSocialSecurityNumber();
   } 
 
} // end class Clerk

public class Customer extends Person {
 
   private BankAccount ba;
 
   // constructors
 
   public Customer ()
   {
      super();
      ba = new BankAccount();
   }
 
   public Customer ( String initialName, int initialAge, double b )
   {
      super (initialName, initialAge);
      ba = new BankAccount (b);
   } 
 
   // returns String representation of Clerk object
   public String toString()
   {
      return getName() + " (" + getAge() + " years old)" +  
         "\n\tbank account balance: " + ba.getBalance();
   } 
 
} // end class Customer

Mock Test is essentially practice before the Lab Test. They just call it that in UK universities.

I am now slowly realizing I know nothing about setting or returning something. What's the point of doing it? Couldn't you just assign the values regulary? So the part from the first code that confuses me is:

 public void setBalance (double b)
    {
	balance = b;
    }
 
    public double getBalance ()
    {
	return balance;
    }
 
    public String toString()
    {
	return "\n\tbalance: " + balance;

Look up "setter" or mutator and "getter" or accessor methods. Their purpose is to provide a "safe" access or interface to an object's attributes by other objects.

Everything aussiemcgr posted, bless his kind heart, is available in the Oracle Java Tutorials and probably your textbook, two places you should be spending all of your free time to discover the information presented during the classes you didn't attend. Read, practice, practice, practice, . . . , practice some more, read, repeat.

Thanks aussie!

You're right Greg. I just wanted to write up a laundry list of stuff I needed to catch up on, but it probably was selfish for someone to figure it out for me.

Thanks again everyone, I'll be off to study my setters, getters, constructors and super().