Static variables in a Java method like in a PHP function behaviour?

Question

knowing that Java is different from PHP, is there a way to reconstruct such a behaviour in Java?:

In PHP I can make something like this:

function a_function() {
    static $var = "something";
    // do something...
}

After I call this function the first time, all subsequent calls to this function would result in a $var not being reset to "something" at all (its value will be preserved across multiple calls to this function, i.e. if the value of $var will be changed while // do something... is executed, then after a subsequent call, the value of $var would be the last assigned value to $var).

I was wondering if there's a same/like method to do this in Java (declaring a static local variable in a method in Java is not possible, so I guess I can achieve this in some other ways). I thought of making a protected or private static field and use it across multiple calls to a method (here a possible way with a boolean):

public class A {
     protected static boolean isSomething = "false";

     public void aMethod() {
         // do something... e.g. change the isSomething boolean 
         // if some condition occurs
     }

}

What do you think about this approach and what would you do in such a case? Are there other ways to accomplish this?

Thanks for the attention!

Yes, you can do it the way you show in your second example. Keep in mind that you will have problems with that pattern in multi-thread situations. — Angelo Fuchs, Dec 21 '14 at 20:02
Possible duplicate: http://stackoverflow.com/questions/2079830/how-do-i-create-a-static-local-variable-in-java — Rigel Bezerra de Melo, Dec 21 '14 at 20:07

Angelo Fuchs · Accepted Answer · 2015-07-24T09:58:02.313

Yes, you can do it the way you show in your second example.

Keep in mind that you will have problems with that pattern in multi-thread situations.

It is also not very elegant as a design choice. And depending on your situation its dangerous and error-prone.

Use with care (that is: don't do this unless you know you need it)

Usually you would want something like that to be thread-save and atomic. You can do it with the volatile keyword if you also take care of synchronization.

public class A {
    private static volatile boolean status = true;
    public flipStatus() {
        synchronized(this) {
            status = !status;
        }
    }
}

Even better is the use of the Atomic classes from java.util.concurrent.atomic

import java.util.concurrent.atomic.*;
public class A {
   private static final AtomicBoolean status = new AtomicBoolean(true);
   public boolean flipStatusToTrue() { // return true if value has been flipped
       return status.compareAndSet(false, true);
   }
   public boolean flipStatusToFalse() { // return true if value has been flipped
       return status.compareAndSet(true, false);
   }
}

Static variables in a Java method like in a PHP function behaviour?

1 Answers1