copy constructor

[Pritam Chatterjee]

how and why to use copy constructors? Example

[Campbell Ritchie]

To create an object identical to the original one.
To prevent the original being altered.

public class Kettle
{
   private int temperature;
   private int content;
   private final int capacity;

   public Kettle(int capacity)
   {
      content = 0; //When you buy a kettle it contains no water
      temperature = Temperatures.ROOM_TEMPERATURE;
      this.capacity = capacity;
   }

/**
 * Copy constructor which creates a Kettle object identical to k.
 *@param k A Kettle object to copy
 */
   public Kettle(Kettle k)
   {
      content = k.content;
      temperature = k.temperature;
      capacity = k.capacity;
   }
 // lots of other methods
}

Kettle k = new Kettle(20);
k.fill(10);
k.boil();
Kettle k2 = new Kettle(k);
k.cool(99);
System.out.println(k);
System.out.println(k2); // Will still be hot

public class Bank
{
   . . .

   public BankAccount getAccountFromNumber(int accountNumber)
   {
       BankAccount ba = accountsMap.get(accountNumber);
       return new BankAccount(ba);
   }
}

Rather than returning the “real” account, you are returning a copy. That allows code to play with the account object without altering the original account object.

[Pritam Chatterjee]

thanks..

[Campbell Ritchie]

You’re welcome