Why don't we have to provide parentheses when initializing an array object in Java?

Question

I'm learning Java from the ground up right now, and one thing I found interesting was that most more complex data structures must be created in this fashion:

ArrayList<String> list = new ArrayList<String>();

On the other hand, one can simply initialize a string by typing

String[] str_array = new String[10];

Why is it not necessary to provide the parentheses usually associated with calling the constructor when initializing an array? Was this just a stylistic choice? It would be awesome if someone with a better understanding of the JVM could offer some insight to sate my curiosity.

Answer 1

The difference between object creation and array creation is this:

• normal classes have constructors that are called.
  • The parentheses in new ArrayList<String>() indicates the constructor call.
  • Even if a constructor has no arguments, the parentheses still have to be present (the same as in a method call without parameters).
• array classes on the other hand have no constructor
  • Although arrays are objects, their classes are created by the JVM and are therefore subject to special handling that other classes cannot have
  • Initializing the array happens as side effect of the anewarray , multianewarray and newarray bytecode instructions.

That array classes have no constructors can be demonstrated by executing

System.out.println(int[].class.getConstructors().length);

which returns 0.

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In the end, this boils down to decisions the language designers made more than 20 years ago and that were influenced by design decision from other existing languages (like C++).

Answer 2

Arrays can't be created in a same way as creating an ArrayList. As user207421 told , "Arrays are designed to initialize in such a way by using [] ". (eg)

ArrayList aList = new ArrayList(); // It is valid

Arrays aArr = new Arrays();// It is invalid. Since there is no public constructor in java.util.Arrays

Source Code : http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/file/be44bff34df4/src/share/classes/java/util/Arrays.java

C & C++ Languages uses the same [] for initialize an array. So that Java also following.