How to initialize all sub NON-Primitive fields of a complex java object when initialize it?

Question

My data model

Class A fieldA1 : primitive dataType fieldA2 : primitive dataType fieldA3 : NON-primitive dataType (Class B) fieldB1 : primitive dataType fieldB2 : primitive dataType fieldB3 : NON-primitive dataType (Class C) fieldC1 : primitive dataType fieldC2 : primitive dataType fieldC3 : NON-primitive dataType (Class D) fieldD1 : primitive dataType fieldD2 : primitive dataType

My complex object is (Class A)

My problem is that
When i try to initialize my complex java object
All sub NON-Primitive fields in the first level will be null
For example

A a = new A(); a.fieldA3 -> null a.fieldA3.fieldB3 -> cant access it (parent is null object) a.fieldA3.fieldB3.fieldC3 -> cant access it (parent is null object)

Any way/patten to make me able
When initialize a complex java object All sub NON-Primitive fields will be initialize also ?

For example

A a = new A(); a.fieldA3 -> new B(); a.fieldA3.fieldB3 -> new C(); a.fieldA3.fieldB3.fieldC3 -> new D();

Mubin · Accepted Answer · 2013-06-13 09:09:06Z

Why not something simple like this?

public class A { B fieldA3; public A() { fieldA3 = new B(); } } public class B { C fieldB3; public B() { fieldB3 = new C(); } }

Renjith · Accepted Answer · 2013-06-13 09:07:57Z

You have to write a constructor in class A and explicitly create all the objects for non-primitive fields.For initialization, you have to go via constructor only.

Kevin Bowersox · Accepted Answer · 2013-06-13 09:08:47Z

Assign an instance of the appropriate type to the field in the constructor.

public class A{ private B fieldA3; public A(){ this.fieldA3 = new B(); } }

Or just assign them in the declaration. Making sure that B,C,D instantiate their fields in their constructors.

public class A{ private B fieldA3 = new B(); public A(){ } }

Saurabh · Accepted Answer · 2013-06-13 09:11:42Z

Initialize the member variables with instance of the class wherever you are declare the variable. So

class A{ private B other; }

becomes

class A{ private B other = new B(..) }

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