Syntax for 'new' in java [duplicate]

Question

This question already has answers here:

Java inner class and static nested class (28 answers)

Closed 10 years ago.

Constructors of non static member classes take an extra hidden parameter which is a reference to an instance of the immediately enclosing class. There is also a syntactic extension of 'new'.

In the below code,

class K{
 static class Ka{
 static class Kb{
 class Kc{
 class Kd{
 }
 }
 }
 }
}
class Test{
 K.Ka.Kb.Kc.Kd k = new K.Ka.Kb().new Kc().new Kd();
}

Can you please help me understand the meaning of Kb() in K.Ka.Kb().new Kc().new Kd()? I understand that new Kc() is required as told in first paragraph.

• QuakeCore: only if you bothered reading this

Answer 1

The parentheses you point out actually do not apply to Kb but K.Ka.Kb.

new K.Ka.Kb()

is creating a new instance of the K.Ka.Kb nested class.

• overexchange: Oh you mean (new K.Ka.Kb()).new Kc().new Kd();?
• overexchange: @SotiriosDelimanolis kc and kd are inner class. But the idiom of saying non static member class as inner class, is it a standard jargon?
• Sotirios Delimanolis: Yes

Answer 2

It's calling the constructor of Kb. It's easier to show this in three statements:

K.Ka.Kb x1 = new K.Ka.Kb();
K.Ka.Kb.Kc x2 = x1.new Kc(); // Pass x1 as the hidden constructor arg
K.Ka.Kb.Kd.Kd k = x2.new Kd(); // Pass x2 as the hidden constructor arg

Answer 3

Kb() is the default constructor for class Kb. It is what relates to the first new of the line:

1. you are creating a new instance of Kb (class K.Ka.Kb actually ; depending on the context you may omit K.Ka.)
2. on which you are calling new Kc() for creating a new instance of Kc
3. on which you are calling new Kd() for creating a new instance of Kd