Java中特殊数组大小声明的正确解读方式咨询

Hey there! Let's break down this specific array declaration piece by piece to clear up any confusion:

1. The Variable Declaration: String[] book #

This part is straightforward:

• String[] defines the type: we're declaring a variable that holds an array of String objects.
• book is the name of our array variable.

2. The Array Initialization: new String[9_999_999 + 1] #

This is where the "special" part comes in—let's split it further:

The Number Literal with Underscores: 9_999_999 #

Starting with Java 7, the language allows using underscores (_) in numeric literals purely for readability. They don't change the actual value of the number at all. So 9_999_999 is exactly equivalent to 9999999; the underscores just make it easier to quickly see this is 9 million (instead of counting digits manually).

The Array Length Calculation: 9_999_999 + 1 #

The expression inside the square brackets [] determines the length of the array. Here, we're adding 1 to 9,999,999, resulting in 10,000,000. This means the array can hold 10 million String elements.

A Quick Note on Array Default Values #

Since String is a reference type in Java, every element in this newly created array will be initialized to null by default until you assign actual String objects to them.

Putting It All Together #

The entire line translates to:

We're creating a variable named book that references a new String array capable of storing 10 million elements. Each element starts as null.

内容的提问来源于stack exchange，提问作者NovDanil