Why is string.length() a method, and int[].length a property?

Question

Why is String.length() a method, and int[].length a property (see below)?

int[] nums = {2,4,7,12,43};
String phrase = "Hello, world.";

System.out.length(nums.length);
System.out.length(phrase.length());

Top voted answer in that 'duplicate' is not particularly useful. — Perception, Feb 13 '13 at 15:02

score 4 · Answer 1 · answered Feb 13 '13 at 14:58

4

I don't think there has to be a good reason, and I think there could be many reasons.

But one is that by making String#length() a property, it can be declared in an interface instead (in this case CharSequence). Interfaces cannot declare public instance fields.

answered Feb 13 '13 at 14:58

Mark Peters

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Good point. But I think `CharSequence` was added in JDK 1.4. But, `String.length()` existed even before that, hence, not sure of the intent of original design. – Bimalesh Jha Feb 13 '13 at 15:16

Bernhard Barker · Answer 2 · 2013-02-13T16:27:04.327

1

This is what the String::length() function looks like:

public int length() {
    return count;
}

So essentially count could've been called length and made public to be similar to arrays (it is final after all).

It was probably just a design decision. There may have been some contributing factors that we can speculate about (one of which could've been the CharSequence thing mentioned by Mark Peters).

edited Feb 13 '13 at 16:27

answered Feb 13 '13 at 15:01

Bernhard Barker

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score 0 · Answer 3 · answered Feb 13 '13 at 15:00

Because String is not an array as such. The designers of Java designed arrays (which are objects) to have a public field named length.

On the other hand, a String has a method which gives the length instead. In general it is a more conventional approach to make member fields private and use methods to access them, but in the case of arrays it is not.

They're different objects with different signatures as far as you are concerned. A String is not a char[] (although internally it might be implemented that way).

score 0 · Answer 4 · answered Feb 13 '13 at 15:07

0

No particular reason, I think. In fact in C#, a very similar language, String.length is a property http://msdn.microsoft.com/en-us/library/system.string.length.aspx. But take a look at what C# designer has to say about this design:

The Length property returns the number of Char objects in this instance, not the number of Unicode characters.
The reason is that a Unicode character might be represented by more than one Char. Use the 
System.Globalization.StringInfo class to work with each Unicode character instead of each Char.

answered Feb 13 '13 at 15:07

Bimalesh Jha

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A property in C# is equivalent to a private field with a getter in Java. The question here is why does Java has not simply made `length` a public final field. – Cyrille Ka Feb 13 '13 at 15:09
@CyrilleKarmann I think it is a public field. Take a look at MSDn example `Console.WriteLine(characters.Length);` – Bimalesh Jha Feb 13 '13 at 15:13

score 0 · Answer 5 · edited May 23 '17 at 12:12

Why int[].length a property?

Arrays are special objects in java, they have a simple attribute named length which is final.

There is no "class definition" of an array (you can't find it in any .class file), they're a part of the language itself.

The public final field length, which contains the number of components of the array. length may be positive or zero.
The public method clone, which overrides the method of the same name in class Object and throws no checked exceptions. The return type of the clone method of an array type T[] is T[].
A clone of a multidimensional array is shallow, which is to say that it creates only a single new array. Subarrays are shared.
All the members inherited from class Object; the only method of Object that is not inherited is its clone method.

Resource: JSL 10.7

Why String.length() a method?

Why is string.length() a method, and int[].length a property?

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