What is the difference between using and not using `New` keyword to define an array? [duplicate]

Answer 1

In your second program, the { ... } are not array delimiters, they are block delimetes; in this case they are used to give a so-called initializer block, which is executed when a new instance of your class is instantiated.

The "correct" way to create an initialized array is:

new byte[] { 1, 2, 3 };

This can be used always, both when the reference is initialized and when an existing reference is used or when the array is passed to a method:

byte[] myArray = new byte[] { 1, 2, 3 };    // OK
myArray = new byte[] { 4, 5, 6 };           // OK
anObject.someMethod(new byte[] { 7, 8, 9}); // OK

However, the first variant is very common and therefore Java allows you to leave the new byte[] part out in that particular case:

byte[] myArray = { 1, 2, 3 };    // OK
myArray = { 4, 5, 6 };           // Does not compile
anObject.someMethod({ 7, 8, 9}); // Does not compile

Answer 2

There is a big difference. The former can be used only during initialization of an array. Code compilation will fail if you try to initialize an already defined / declared array with an array constant expression like {1,2,3} The latter can be used any-time. The byte-code is same in both cases.