are wrapper classes intialized to zero?

[archu sweet]

if we declare Integer i;

does i get intialized to zero???

[Matthew Brown]

No. Because it's a reference type, it gets initialised to null. Assuming you're talking about a member variable, that is - variables declared in methods aren't initialised to anything.

[marc weber]

Hmmm... If only there were some way to test this.

[kumarjit banerjee]

archu sweet wrote:if we declare Integer i;

does i get intialized to zero???

Consider the following example

public class Demo{
  Integer i;
  public static void main(String[] args){
    System.out.println(i);
  }
}

The output of the program is null. The reason is that when Integer i; is declared the reference variable i is initialized to null since it is an instance variable. Now the obvious question is that the program should throw a NullPointerException but this not the case.
System.out.println(i); invokes the below overloaded version of println of the class java.io.PrintStream.

public void println(Object x) {
        String s = String.valueOf(x);
        synchronized (this) {
            print(s);
            newLine();
        }
    }

Now consider the below method of java.lang.String

 public static String valueOf(Object obj) {
        return (obj == null) ? "null" : obj.toString();
    }

This provides the solution to the query.

[Jesper de Jong]

Kumarjit: Thanks for your answer. Please UseCodeTags when you post source code - as you can see, the code will be formatted in a much more readable way when you use them.

Anchu: As you can see, you could have checked this out yourself by writing a small program. Try writing lots of little programs to test out features of Java - trying things out yourself is one of the best ways to learn.

[abalfazl hossein]

Why classes like "Integer" called wrapper?What is the reason?

[Wouter Oet]

Because they wrap around a primitive. That way you can store primitives in a Collection.