Java initial values?

Question

If I were to do something such as:

public class Game
{
    private boolean RUNNING = true;

    Game()
    {
    }

    public static void main(String[] args)
    {
        Game game = new Game();
    }
}

At what point in time would RUNNING = true?

edit: for clarity, at what point in the program would running be set to true. ex: Before the constructor, after the constructor, etc.

It's a good question. When you create an object there's a certain order how things are initialized. It's not just "all the time", I'm sorry. — Thomas Uhrig, May 26 '13 at 18:08
@Lemmons In that case, I'd update the question to reflect ordering and such, otherwise, it's not clear from the title. — raffian, May 26 '13 at 18:10
@ThomasUhrig: With a more comprehensive example code (e.g. with multiple members to initialize, static initializers, etc.), it might be a good question ;) — Oliver Charlesworth, May 26 '13 at 18:17

score 4 · Accepted Answer · answered May 26 '13 at 18:06

4

It will be set to true before the constructor. You can use it in the constructor as true.

answered May 26 '13 at 18:06

mwerschy

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Eng.Fouad · Answer 2 · 2013-05-26T18:42:07.163

This code explains itself:

public class SuperClass
{
    String superField = getString("superField");

    public SuperClass()
    {
        System.out.println("SuperClass()");
    }

    public static String getString(String fieldName)
    {
        System.out.println(fieldName + " is set");
        return "";
    }

    public static void main(String[] args)
    {
        new ChildClass();
    }
}

class ChildClass extends SuperClass
{
    String childField = getString("childField");

    public ChildClass()
    {
        System.out.println("ChildClass()");
    }
}

OUTPUT:

superField is set
SuperClass()
childField is set
ChildClass()

sp00m · Answer 3 · 2013-05-26T18:17:49.173

0

private boolean RUNNING = true;
Game() {
}

is exactly the same as

private boolean RUNNING;
Game() {
    RUNNING = true;
}

Actually, the comiler will move the initialization at the beginning of the constructor. The value will then be set when instantiating an object of that class.

edited May 26 '13 at 18:17

answered May 26 '13 at 18:11

sp00m

47,968
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score 0 · Answer 4 · edited May 23 '17 at 12:18

When the constructor is called using the new operator all non-static members of the class are initialized before the code inside the constructor is executed. You can use the debugger and step into that call and see where it goes first. Static members are initialized when the class is loaded and for the first time accessed (see this question for more detailed info about static members).

score 0 · Answer 5 · answered May 26 '13 at 18:53

When you try to use local variables which not manually initialized, you will get a compile time error.

public static void main(String args[]){
               int a;
              System.out.pritnln(a); //error
      }

But it's not the case with instance variables. This itself shows that they are ready for usage before the constructor even.

   public class Example{
            private int a;
            public Example(){
                   System.out.println(a);   //No error
            }
            public int getA(){
                   return a;           //No error
            }
   }

I hope this intuition answers your question..........

Java initial values?

5 Answers5