java相当于ruby的|| =语法

Question

I'm brand new to java, coming from a ruby world. One thing I love about ruby is the very terse syntax such as ||=.

I realize of course that a compiled language is different, but I'm wondering if Java has anything similar.

In particular, what I do all the time in ruby is something like:

someVar ||= SomeClass.new

I think this is incredibly terse, yet powerful, but thus far the only method I can think of to achieve the same thing is a very verbose:

if(someVar == null){
  someVar = new SomeClass()
}

Just trying to improve my Java-fu and syntax is certainly one area that I'm no pro.

Answer 1

No, there's not. But to replace

if(someVar == null){
  someVar = new SomeClass()
}

something similar is scheduled for Java 7 as Elvis Operator :

somevar = somevar ?: new SomeClass();

As of now, your best bet is the Ternary operator :

somevar = (somevar != null) ? somevar : new SomeClass();

Answer 2

我认为你能做的最好的是三元运算符：

someVar = (someVar == null) ? new SomeClass() : someVar;

Answer 3

There is no equivalent in Java. Part of the reason for this is that null is not considered false .

So, even if there was a logical OR-assignment keyword, you have to remember that:

Object x = null;
if (!x) { // this doesnt work, null is not a boolean

Answer 4

This looks like you could add a method to SomeClass similar to

public static someClass enforce(someClass x)  {
 someClass r = x.clone();
 if(r == null){
  r = new SomeClass();
 }

 return r;
}

And call it like

someVar = SomeClass.enforce(someVar);