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.

Solution 1

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.

Solution 2

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".

Solution 3

No, it's not possible in java.

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

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

Solution 4

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.

Solution 5

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.

View more solutions

Comments

[khachik]

Keep efficiency in mind efficiency of what?

[user83643]

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.

[Simeon]

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.

[Amit Kumar Gupta]

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.

[Adam Gent]

@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.

[Brian Roach]

+1 for pointing out that what he's trying to do isn't the norm.

[bcorso]

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.

[Ranjit]

this is for String, but how for integers ?? int day, month, year, hour, min = day = month = year = hour = 0; is it right ??

[GKFX]

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.

[Aequitas]

Are these the same object? If I later do one = "cat" will two.equals("cat") return true?

[IgorGanapolsky]

The only caveat is that this wouldn't work for static variables.

[IgorGanapolsky]

What about integer declarations?

[TheCrazyProfessor]

Why does this not work with Calendar? if you do that every variable behave like its the same when you manipulate one of them

[Neuron]

what do you mean with "misbehave"? It will behave differently then 3 separately initialised objects, but it really depends on what you want..

[Neuron]

Can you explain why this should be avoided?

[Yuhang Lin]

@Lonely Neuron I think it's easy to make a mistake if you use it in this way.

[Neuron]

@YuhangLin i was just hoping for a better answer

[Alexander Heim]

@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.

[Neuron]

@AlexanderHeim Thanks for the explanation. But the reason I asked was because it should be part of the answer.

[Cristian Gutu]

@AlexanderHeim why is it slower?

[starscream_disco_party]

@Zeeen try it in your Groovy interpreter!

[Zeeen]

That is groovy, not plain old Java. also it doesn't work on regular java, I just tested it.

[starscream_disco_party]

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)_/¯