Initializing multiple variables to the same value in Java

Question

I'm looking for a clean and efficient method of declaring multiple variables of the same type and of the same value. Right now I have:

String one = "", two = "", three = "" etc...

But I'm looking for something like:

String one,two,three = ""

Is this something that is possible to do in java? Keeping efficiency in mind.

Length of code, time to type, visually simple. That's what I mean. I know that reserving memory is reserving memory and that this question is related to the 'human' side of things. — user83643, Jun 01 '11 at 14:33
I'd say that this is generally against accepted Java conventions, it will surprise the reader and IMHO is harder to read than declaring them on separate lines. — Simeon, Jun 01 '11 at 14:39
I checked for the performance (on java 8) a = b =c = d =e = true takes 2x+ times than a = true; b = true ; and so on. — Amit Kumar Gupta, Aug 13 '15 at 05:34
@AmitKumarGupta I tested it on JDK16 and I found no discernible difference using JMH. How did you test? Also once you assign one,two,three something other than a constant it becomes the same (multiple assignment). In fact multiple variable assignment can be leveraged when dealing with multithreaded code since DUP uses the stack. — Adam Gent, Jun 02 '21 at 16:52

score 385 · Accepted Answer · edited Apr 28 '18 at 00:37

385

String one, two, three;
one = two = three = "";

This should work with immutable objects. It doesn't make any sense for mutable objects for example:

Person firstPerson, secondPerson, thirdPerson;
firstPerson = secondPerson = thirdPerson = new Person();

All the variables would be pointing to the same instance. Probably what you would need in that case is:

Person firstPerson = new Person();
Person secondPerson = new Person();
Person thirdPerson = new Person();

Or better yet use an array or a Collection.

edited Apr 28 '18 at 00:37

Neuron

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answered Jun 01 '11 at 14:35

Alfredo Osorio

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There are cases where this makes sense for mutable objects as well. For instance, in the constructor of linkedlist implementation where initially: head = tail = new Node(value). So both head and tail should point to the same reference. – bcorso Oct 20 '13 at 19:01
Are these the same object? If I later do `one = "cat"` will `two.equals("cat")` return true? – Aequitas Sep 24 '15 at 05:48
The only caveat is that this wouldn't work for static variables. – IgorGanapolsky Nov 30 '15 at 15:15
What about integer declarations? – IgorGanapolsky Sep 05 '17 at 12:34
Why does this not work with Calendar? if you do that every variable behave like its the same when you manipulate one of them – TheCrazyProfessor Jan 26 '18 at 08:15

score 75 · Answer 2 · edited Jun 16 '18 at 13:37

75

You can declare multiple variables, and initialize multiple variables, but not both at the same time:

 String one,two,three;
 one = two = three = "";

However, this kind of thing (especially the multiple assignments) would be frowned upon by most Java developers, who would consider it the opposite of "visually simple".

edited Jun 16 '18 at 13:37

Kasun Siyambalapitiya

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answered Jun 01 '11 at 14:37

Michael Borgwardt

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+1 for pointing out that what he's trying to do *isn't* the norm. – Brian Roach Jun 01 '11 at 14:37
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this is for String, but how for integers ?? int day, month, year, hour, min = day = month = year = hour = 0; is it right ?? – Ranjit Nov 16 '13 at 09:56

Saurabh Gokhale · Answer 3 · 2011-06-01T14:39:37.753

28

No, it's not possible in java.

You can do this way .. But try to avoid it.

String one, two, three;
one = two = three = "";

edited Jun 01 '11 at 14:39

answered Jun 01 '11 at 14:34

Saurabh Gokhale

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Can you explain why this should be avoided? – Neuron Apr 28 '18 at 00:39
@Lonely Neuron I think it's easy to make a mistake if you use it in this way. – Yuhang Lin Sep 02 '18 at 14:41
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@YuhangLin i was just hoping for a better answer – Neuron Sep 02 '18 at 14:46
@LonelyNeuron Well for one it´s slower. It takes almost twice the time as if you would just initialize seperately. One the other this "feature" is unnecessary. I can´t think of a scenario that wouldn´t be solvable by using a different approach. It´s simply said not a clean code. – Alexander Heim Feb 11 '19 at 14:22
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@AlexanderHeim Thanks for the explanation. But the reason I asked was because it should be part of the answer. – Neuron Feb 11 '19 at 14:27
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@AlexanderHeim why is it slower? – Cristian Gutu Mar 24 '20 at 18:46

score 23 · Answer 4 · edited Apr 28 '18 at 00:38

23

Works for primitives and immutable classes like String, Wrapper classes Character, Byte.

int i=0,j=2   
String s1,s2  
s1 = s2 = "java rocks"

For mutable classes

Reference r1 = Reference r2 = Reference r3 = new Object();`

Three references + one object are created. All references point to the same object and your program will misbehave.

edited Apr 28 '18 at 00:38

Neuron

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answered Aug 21 '12 at 18:03

Srujan Kumar Gulla

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I disagree with "All references pointing to same object and your program will misbehave." The only problem is that what happens to the object of one reference happens to the object of another reference -- because it's the same object. This isn't misbehaviour; it's how Java works. – GKFX Jul 20 '14 at 15:04
1

what do you mean with "misbehave"? It will behave differently then 3 separately initialised objects, but it really depends on what you want.. – Neuron Apr 28 '18 at 00:39

score 17 · Answer 5 · answered Aug 10 '15 at 00:53

17

You can do this:

String one, two, three = two = one = "";

But these will all point to the same instance. It won't cause problems with final variables or primitive types. This way, you can do everything in one line.

answered Aug 10 '15 at 00:53

hyper-neutrino

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This is also works with final vars. Ex: public static final String ONE, TWO = ONE = "Blah"; Not only are all vars defined & initialized to the same value, but the split definition & assignment of var ONE doesn't violate the final limitation; it's considered a single expression. – Yurelle Aug 24 '23 at 18:39

score 2 · Answer 6 · answered Jun 01 '11 at 14:31

2

I do not think that is possible you have to set all the values individualling (like the first example you provided.)

The Second example you gave, will only Initialize the last varuable to "" and not the others.

answered Jun 01 '11 at 14:31

RMT

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starscream_disco_party · Answer 7 · 2021-03-26T15:02:28.857

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Edit: As Zeeen pointed out this will not work in Java. The question I'd intended to answer was in Groovy as well, this was submitted in error.

Way too late to this but the simplest way I've found is:

String foo = bar = baz = "hello"
println(foo)
println(bar)
println(baz)

Output:

hello
hello
hello

edited Mar 26 '21 at 15:02

answered Jun 25 '20 at 14:17

starscream_disco_party

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@Zeeen try it in your Groovy interpreter! – starscream_disco_party Mar 26 '21 at 14:40
That is groovy, not plain old Java. also it doesn't work on regular java, I just tested it. – Zeeen Mar 26 '21 at 14:52
ah yeah look at that, must have gotten some tabs mixed up when i submitted this answer. at least it looks like it helped some other confused person ¯\\_(ツ)_/¯ – starscream_disco_party Mar 26 '21 at 14:59

Initializing multiple variables to the same value in Java

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