How to define a multidimensional array in Java using curly braces?

Question

I don't understand the behaviour of Java about arrays. It forbids to define an array in one case but allows the same definition in another.

The example from tutorial:

String[][] names = {
        {"Mr. ", "Mrs. ", "Ms. "},
        {"Smith", "Jones"}
    };
System.out.println(names[0][0] + names[1][0]);    // the output is "Mr. Smith";

My example:

public class User {
   private static String[][] users;
   private static int UC = 0;

   public void addUser (String email, String name, String pass) {
      int i = 0;

      // Here, when I define an array this way, it has no errors in NetBeans
      String[][] u = { {email, name, pass}, {"[email protected]", "jack sparrow", "12345"} };

      // But when I try to define like this, using static variable users declared above, NetBeans throws errors
      if (users == null) {
         users = { { email, name, pass }, {"one", "two", "three"} };    // NetBeans even doesn't recognize arguments 'email', 'name', 'pass' here. Why?

         // only this way works
         users = new String[3][3];
         users[i][i] = email;
         users[i][i+1] = name;
         users[i][i+2] = pass;
         UC = UC + 1;
      }
    }

The mistakes thrown by NetBeans are:

illegal start of expression,

";" expected,

not a statement.

And also it doesn't recognize arguments email, name, pass in the definition of the users array. But recognizes them when I define u array.

What is the difference between these two definitions? Why the one works but the another one defined the same way doesn't?

Sergey Kalinichenko · Accepted Answer · 2012-05-22 18:13:00Z

12

You need to add new String[][] before the array aggregate:

users = new String[][] { { email, name, pass }, {"one", "two", "three"} };

answered May 22, 2012 at 18:13

Sergey Kalinichenko

729k85 gold badges1.2k silver badges1.6k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Green Over a year ago

But I have done this already. Right below the line of "public class User {" is the line "private static String[][] users"

Sergey Kalinichenko Over a year ago

@Green The new String[][] part is implied when you combine initialization and declaration; when you declare a field or a variable in one place, but initialize it in a different place, you need to explicitly provide the type of the object that you are creating before the array aggregate.

Óscar López · Accepted Answer · 2012-05-22 18:14:29Z

6

You can use this syntax:

String[][] u = {{email, name, pass}, {"[email protected]", "jack sparrow", "12345"}};

Only when you're declaring the matrix for the first time. It won't work for assigning values to a String[][] variable after you've declared it elsewhere, that's why users = ... fails. For assigning values to an already-declared String[][] (or a matrix of any other type for that matter), use

users = new String[][] { { email, name, pass }, {"one", "two", "three"} };

answered May 22, 2012 at 18:14

Óscar López

237k38 gold badges321 silver badges391 bronze badges

Comments

Moha Dehghan · Accepted Answer · 2012-05-22 18:14:03Z

2

The first case is an initialization statement, while the second is only an assignment. That kind of filling arrays is only supported when defining a new array.

answered May 22, 2012 at 18:14

Moha Dehghan

18.5k3 gold badges60 silver badges74 bronze badges

Comments

Marcos · Accepted Answer · 2012-05-22 18:16:55Z

2

For re-assigning the matrix you must use new:

users = new String[][] {{email, name, pass }, {"one", "two", "three"}};

answered May 22, 2012 at 18:16

Marcos

4,6637 gold badges35 silver badges62 bronze badges

Collectives™ on Stack Overflow

How to define a multidimensional array in Java using curly braces?

4 Answers 4

2 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related