copy constructor in java

Question

class Client{
private String name;
private int age;
private int amount;
public Client(Client otherClient){
    name=otherClient.name;
    age=otherClient.age;
    amount=otherClient.amount;
    }
}

What if I want to use this later on:

Client c1=new Client("Smith");

or

Client c1=new Client("Smith",20);

or

Client c1=new Client("Smith",20,100);

How can I have optional parameters? Do I have to define constructors for each case? Thanks

Answer 1

First answer is absolutely correct, but if you really want to have only one constructor for all these cases, you can write something like this:

public Client(String name, Integer age, Integer amount) {
    this.name = name;

    if (age != null) {
        this.age = age;
    }

    if (amount != null) {
        this.amount = amount;
    }
}

Usage:

Client c1 = new Client("Smith", null, null);
Client c2 = new Client("Smith", 20, null);
Client c3 = new Client("Smith", null, 100);
Client c4 = new Client(null, 20, 100);
Client c5 = new Client("Smith", 20, 100);

Pay attention that I used wrapper class Integer instead of int in constructor arguments because variable of int type can't be null.

---

Also, if you make your setters return this, you'll simulate kind of named arguments in Java:

new Client().setName("Smith").setAge(20).setAmount(100)

Answer 2

Yes, you have to overload the constructor, which is something you should read up on. It allows you to provide multiple input parameters for a method. The compiler will choose the appropriate method when the method is called.

Here are the Javadocs on overloading: http://docs.oracle.com/javase/tutorial/java/javaOO/methods.html