如何使用花括号在 Java 中定义多维数组？
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How to define a multidimensional array in Java using curly braces?
提问by Green
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.
我不明白 Java 关于数组的行为。它禁止在一种情况下定义数组，而在另一种情况下允许相同的定义。
The example from tutorial:
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";
My example:
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}, {"[email protected]", "Hyman 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:
NetBeans 抛出的错误是：
illegal start of expression,
表达式的非法开始，
";" expected,
";" 预期，
not a statement.
不是声明。
And also it doesn't recognize arguments email, name, passin the definition of the usersarray. But recognizes them when I define uarray.
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数组时会识别它们。
What is the difference between these two definitions? Why the one works but the another one defined the same way doesn't?
这两个定义有什么区别？为什么一个有效，而另一个以相同方式定义的无效？
回答by dasblinkenlight
You need to add new String[][]before the array aggregate:
您需要new String[][]在数组聚合之前添加：
users = new String[][] { { email, name, pass }, {"one", "two", "three"} };
回答by óscar López
You can use this syntax:
您可以使用以下语法：
String[][] u = {{email, name, pass}, {"[email protected]", "Hyman sparrow", "12345"}};
Onlywhen you're declaring the matrix for the first time. It won't work for assigning values to a String[][]variable afteryou'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
仅当您第一次声明矩阵时。在其他地方声明String[][]变量后，它无法为变量赋值，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"} };
回答by Enrique Marcos
For re-assigning the matrix you must use new:
要重新分配矩阵，您必须使用new：
users = new String[][] {{email, name, pass }, {"one", "two", "three"}};
回答by Mohammad Dehghan
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.
第一种情况是初始化语句，而第二种情况只是赋值。只有在定义新数组时才支持这种填充数组。
