Passing a string to a string array reference

Question

I'm somewhat confused about the code below:

class BooksTestDrive {
  public static void main(String [] args) {
      String [] islands = new String[4];

      islands[0] = "Bermuda";
      islands[1] = "Fiji";
      islands[2] = "Azores";
      islands[3] = "Cozumel";


  }
}

I was under the assumption that this would return a NullPointerException error because no object is initialized.

I assumed I would need to do

class BooksTestDrive {
  public static void main(String [] args) {
      String [] islands = new String[4];
      islands[0] = new String();

//    etc..

      islands[0] = "Bermuda";
      islands[1] = "Fiji";
      islands[2] = "Azores";
      islands[3] = "Cozumel";


  }
}

Why is it okay here? Why is the exception not thrown?

Juvanis · Accepted Answer · 2013-01-12 10:32:27Z

3

"Bermuda" is a String literal and String str = "Bermuda"; implies that str is a new String object with the value "Bermuda".

String str = "Bermuda";
String str = new String("Bermuda");

The lines above do the same work, but with one difference, first string instance is managed by Java String constant pool and the second one is not.

answered Jan 12, 2013 at 10:32

Juvanis

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3 Comments

Lion Over a year ago

I see. So if It was lets say NotAStringClass[] islands = new NotAStringClass[4]; then passing a string to islands[0] would not work, correct?

Juvanis Over a year ago

@Lion you don't see, sorry. islands[0] = "Bermuda"; and islands[0] = new String("Bermuda"); functionally do the same thing and both will work, but created String objects for these 2 assignments live in different places in memory.

Lion Over a year ago

Got it. Your answer along with Hassan's helped me get it. Thanks :)

hmatar · Accepted Answer · 2013-01-12 10:32:52Z

0

Exception is not thrown because you are using "static" strings whose memories are implicitly created and the references assigned to islands[i]

answered Jan 12, 2013 at 10:32

hmatar

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2 Comments

Lion Over a year ago

I get it now. Thanks, you and Shekasteh helped me understand it. I can only select one answer so I'll just pick his but thank you both.

hmatar Over a year ago

Any time Lion! I am happy that you understood the concept.

Chris · Accepted Answer · 2013-01-12 10:36:33Z

0

You're doing nothing wrong, the compiler honors that and it's running also.

When you're using static string literals the string object is created implicit. You can also try this out with the debugger, your String "Bermuda" has an object id.

answered Jan 12, 2013 at 10:36

Chris

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Comments

Niar · Accepted Answer · 2013-01-12 10:52:38Z

0

The Exception that you asked about occurs when you declare a variable but did not create an object. In the line "String [] islands = new String[4]; " the new keyword is used to instantiate (or create) an object of type Integer and the pointer variable islands is assigned this object. So you will not get an exception.

answered Jan 12, 2013 at 10:52

Niar

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