Length field and Length () method in Java

This article mainly describes the length field in Java and the length () method, the need for friends can refer to the following, more Java tutorial knowledge, please visit the Crazy Software Education website.

First of all, can you answer the following questions quickly?

How do I get the length of an array and string without the auto-complete functionality of the IDE (integrated development environment)?

I asked different levels of developers (beginner and intermediate) the same questions, and they were hard pressed to give an accurate and assured answer. Although the IDE provides the code auto-complete functionality is very convenient, but also brings a "surface understanding" problem. In this article, I'll explain some of the key concepts of Java arrays.

The answers to the above questions are as follows:

int[] arr = new INT[3];

System.out.println (arr.length);//The Length property of the array

String str = "ABC";

System.out.println (Str.length ());//The length () method of the string

The question now is, why does the array have the length property and the string does not? Or, why does the string have the length () method and the array does not?

Question 1. Why does an array have the length property?

First, an array is a container object that holds a certain number of values for a certain type. When an array is created, its length is no longer changed. The length of the array is visualized as a final instance variable. Therefore, the length can be considered as an attribute of the array definition.

There are two ways to create an array: 1) array creation expressions, 2) array initialization. Once the array is created, its length is fixed.

The following array declaration, while only indicating the length of the first dimension in the array, is legal.

int[][] arr = new int[3][];

The initialization of an array creates an array and assigns an initial value to each of these elements, which is made up of a comma-delimited number of expressions surrounded by "{" and "}", as shown in the following example:

Int[] arr = {1, 2, 3};

Question 2. Why isn't there an "Array" class defined like "String"?

Because the array is an object, the following code is legal.

Object obj = new INT[10];

The array contains all the members (except clone) in the object class. Why can't you define an array like a class? We can't find a Array.java file. A relatively simple explanation is that they are hidden. Consider this question: If you have an array class, what is it like? We still need an array to hold the array data, don't we? Therefore, it is unwise to define a similar one.

In fact, we can get an array class in the following way:

int[] arr = new INT[3];

System.out.println (Arr.getclass ());

The result of the output is:

Class[]

"Class[" is the run-time type signature of the "array of type int" class object.

Question 3. Why does the string have the length () method?

A data structure that holds character data in a string is an array of characters. Therefore, it is not necessary to define a field that is not required in the actual application. It doesn't work with C, in Java, a character array is not a string.

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Length field and Length () method in Java