Confusion on creating new instances in java

Question

I am not sure why this line of code does not work in java:

    Point point1 = (1,2);

Instead it should be like this:

    Point point1 = new Point(1,2);

As you say, the first is incorrect and the second is correct. But what's your question? — Ted Hopp, Sep 04 '15 at 04:25
@FiidoFirdauz yes I did, but I don't know how to explain why it doesn't work. — munmunbb, Sep 04 '15 at 04:32
Coz that's the java syntax. Please read a book of Java. Objects, Classes etc and then comes instantiating of objects. Please do some basic homework and post questions that stops you from moving on with understanding. — Karthik R, Sep 04 '15 at 04:33
@wendyWangbbg - because `new` keyword is one of the ways to create a "new" instance. That's the syntax — TheLostMind, Sep 04 '15 at 04:34
@TheLostMind, I disagree with closing this as a dup to that. This, as you elude to in your comment, can and should be answered in a grammar context. That question clearly isn't asking the same thing - or so it appears to me. — ChiefTwoPencils, Sep 04 '15 at 05:07

CollinD · Accepted Answer · 2015-09-04T05:26:20.180

4

Whenever you want to instantiate an object in Java, excepting primitive types (long, int, bool, etc), you will need to use the new operator.

(1,2) is not a valid Java object literal and as such cannot be instantiated to a type of Point.

Instead, you will need to instantiate the object with new and call the (int, int) constructor.

That looks like your second example

Point point = new Point(1, 2);

The only time you can instantiate without new is when using a valid literal (or array initializer) that can be instantiated

All completely valid:

String x = "NewString";
int y = 5;
double z = 3.14;
int[] x = {1,2,3}; //creates an array in one swoop!

Not sure what your question was, but I hope this clears it up.

edited Sep 04 '15 at 05:26

answered Sep 04 '15 at 04:31

CollinD

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I guess she wanna some good explanation. Good Collin and i like ur photo haha – Fiido93 Sep 04 '15 at 04:33
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There's one other case where an object can be created without using the `new` operator, and that is with [array initializers](http://docs.oracle.com/javase/specs/jls/se8/html/jls-10.html#jls-10.6). So you can do things like `int ia[][] = { {1, 2}, null };`. That's completely equivalent to `int ia[][] = new int[][] { new int[] {1, 2}, null };` but much nicer to write. – Ted Hopp Sep 04 '15 at 05:23
I think that still falls under the category of valid literals. But it's definitely not intuitive from my answer. I'll throw that in, thanks Ted! – CollinD Sep 04 '15 at 05:25
Well, it doesn't have to be literals. You can also write `int[] x = { foo(), bar() };` (where `foo()` and `bar()` are methods that return `int` values). – Ted Hopp Sep 04 '15 at 05:26
It's definitely moot at this point, but out of curiosity does that still, in fact qualify as a literal? I suppose not since it has nested dynamic values, but the array itself is still somewhat literally defined. I think you're right though, that wouldn't qualify as a literal since it's not literal thru-and-thru. I think that makes array initializers more of a syntactic sugar than anything else. – CollinD Sep 04 '15 at 05:28
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That's my point -- it is not a literal but it is a valid array initializer expression (just not a compile-time constant). – Ted Hopp Sep 04 '15 at 05:29
@TedHopp - Also, `MyClass.newInstance()` is another way of getting a *new* instance – TheLostMind Sep 04 '15 at 05:57

Confusion on creating new instances in java

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