Java中静态初始化和动态初始化之间的区别是什么？ [英] what's the differences between static initialization and dynamic initialization in Java?

问题描述

最近当我在LeetCode上做一些练习时，我发现了一些技巧解决方案。它使用Object o来引用数组 Object o = new Object [] {null，null}; ，我想也许是因为在java中一切都是object.But当我尝试这种方式时，它出错了。 Object o3 = {1,2}; 所以我尝试各种方式初始化数组，我想看到差异，比如这些

Recently when I do some practice on LeetCode,I find some trick solution.It use an Object o to reference an arrayObject o = new Object[]{null,null};,I guess maybe it's because in java everything is object.But when I tried this way,it went wrong.Object o3 = {1,2};So I tried every way to initialization a array and I want to see the difference,like these

int arr[] = {1,2};
Object o = arr;
Object o1 = new int[2];
Object o2 = new int[]{1,2};
Object o3 = {1,2};

只有o3会编译错误。我不知道是不是因为初始化的方式。我知道当我使用静态初始化时它将首先分配内存，当使用动态初始化时它不会。它们之间的任何其他差异会导致此错误吗？当我使用new创建数组时。它在jvm中做了什么？提前感谢。

Only the o3 will compile an error.I don't know if it's because the way of initialization.I know when I use static initialization it will allocate memory first,when use dynamic initialization it will not.Any other differences between them cause this error?When I use new to create a array.what did it do in jvm?Thanks in advance.

推荐答案

初始值设定项 {1,2} 是<$的简写c $ c> new int [] {1,2} 。此简写只能用作 int [] 。 ¹ 类型变量的初始化程序。例如，以下工作原理：

The initializer {1,2} is shorthand for new int[] {1,2}. This shorthand can only be used as an initializer for a variable of type int[].¹ For instance, while the following works:

int arr[] = {1,2};

这不是：

int arr[];
arr = {1,2}; // ERROR

相反，您需要使用：

int arr[];
arr = new int[] {1,2};

同样，您可以使用：

Object o3 = new int[] {1,2};

P.S。以上内容适用于 static 以及实例字段，也适用于局部变量。 Java没有静态与动态初始化这样的区别。这是更多的C ++术语。

P.S. The above applies to static as well as instance fields, and also to local variables. Java doesn't have such a distinction as "static vs. dynamic initialization". That's more C++ terminology.

  ¹ _{嗯，它也可能是类型的变量byte [] ， long [] ，
float [] ， Integer [] 等，文字 1 和 2 分配兼容。请参阅 Java语言的第10.6节规范。}

 ¹_{Well, it could also be for a variable of type byte[], long[], float[], Integer[], etc., for which the literals 1 and 2 are assignment compatible. See the Section 10.6 of the Java Language Specification.}

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