如何使用花括号在Java中定义多维数组？

Question

我不了解Java关于数组的行为.它禁止在一种情况下定义数组,但在另一种情况下允许相同的定义.

教程中的示例:

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

我的例子:

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}, {"one@one.com", "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;
      }
    }

NetBeans引发的错误是:

非法开始表达,

";" 预期的,

不是声明.

而且它不承认的论点email,name,pass在定义users数组.但是当我定义u数组时识别它们.

这两个定义有什么区别？为什么一个工作但另一个定义相同的方式不？

Answer 1

您需要new String[][]在数组聚合之前添加:

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

Answer 2

您可以使用以下语法:

String[][] u = {{email, name, pass}, {"one@one.com", "jack sparrow", "12345"}};

只有当你第一次声明矩阵时.在您在其他地方声明String[][]变量后,它将无法为变量赋值,这就是users = ...失败的原因.要将值分配给已声明的String[][](或任何其他类型的矩阵),请使用

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