Java的怪异行为阵 [英] Java weird array behavior

问题描述

为什么这个作品：

int[] array = {1, 2, 3};

但这并不：

int[] array;
array = {1, 2, 3};

如果我有一个数组实例变量，我想在我的构造函数来初始化它肯定我没有去。

If I have an array instance variable and I want to initialize it in my constructor surely I don't have to go

array = new int[3];
array[0] = 1;
array[1] = 2;
array[2] = 3;

我觉得我失去了一些东西？

I feel like I'm missing something here?

推荐答案

的 {...} 构建这里被称为Java中的数组初始化。它是一种特殊的速记即只在特定的语法构造可用

The {...} construct here is called an array initializer in Java. It is a special shorthand that is only available in certain grammatical constructs:

这是数组初始化的可在声明中指定，或作为数组创建前pression的一部分，创建一个数组并提供一些初始值。 [...]数组初始化写成逗号分隔的前pressions列表，括在大括号{和 }。

JLS 10.6 Array Initializers

An array initializer may be specified in a declaration, or as part of an array creation expression, creating an array and providing some initial values. [...] An array initializer is written as a comma-separated list of expressions, enclosed by braces "{" and "}".

按规定，你只能用这种速记无论是在声明或数组创建前pression。

As specified, you can only use this shorthand either in the declaration or in an array creation expression.

int[] nums = { 1, 2, 3 };       // declaration

nums = new int[] { 4, 5, 6 };   // array creation

这就是为什么以下不会编译：

This is why the following does not compile:

// DOES NOT COMPILE!!!
nums = { 1, 2, 3 };

// neither declaration nor array creation,
// array initializer syntax not available

还要注意的是：

• 接着后面的逗号可能会出现;它将被忽略


• 您可以的巢的，如果你初始化元素类型本身是一个数组的数组初始化

• A trailing comma may appear; it will be ignored
• You can nest array initializer if the element type you're initializing is itself an array

下面是一个例子：

    int[][] triangle = {
            { 1, },
            { 2, 3, },
            { 4, 5, 6, },
    };
    for (int[] row : triangle) {
        for (int num : row) {
            System.out.print(num + " ");
        }
        System.out.println();
    }

上面打印：

1 
2 3 
4 5 6 

另请参见

• Java教程/螺母和螺栓/阵列


• java.util中。阵列 - 有许多阵列相关的实用方法，如等于，的toString 等



See also

• Java Tutorials/Nuts and Bolts/Arrays
• java.util.Arrays - has many array-related utility methods like equals, toString, etc

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