Initialization with an empty string to an instance of Java String type

What is the String type after all?

I just thought I was taking a bath. In the Java language, literals are the values of primitive types, String types, and null types that are directly represented in the code. Primitive types have different characteristics from reference types, "that's why it can't be helped" (although you shouldn't say that), and null types are also "null", so you can directly describe and handle that data. I can agree with that. Then why is there a literal only for String in the reference type? Why? Why is it sensuously? I thought. Alright, let's find out.

My environment

For the time being, look at the String type

This is the beginning of all the mistakes, but since it is a string "literal" (meaning "literally") in the first place, it is the String itself. But "empty". Not null, but "empty". "Sky" is a fairly important concept, isn't it? I don't think it's written that you can understand why string literals were prepared even if you go to see the String class. But without any thought, I vaguely pressed the F3 key and went to see the String class. Hello. One hour of my mystery. The first thing that jumps in


private final char value[];

Field. It is an array of immutable char values that stores String type string data. Since the sequence and flow are important, it is called a sequence. I learned at first that new data will be generated when new. That's why you can use StringBuilder for modifiable strings.

Looking at the beginning of the huge number of constructors, it seemed like "Yeah," and I was surprised even now.


public String() {
    this.value = "".value;

public String(String original) {
    this.value = original.value;
    this.hash = original.hash;

//Omitted below

What happens with this.value =" ". value;? is. I see that it is initialized with String str =" "; because it is an empty string, and I learned it a long time ago, but when I think about it, I think that char c =''; is impossible. .. Isn't it possible to create an instance but not assign an initial value? ?? ??

String str = "";
System.out.println(str.length()); // 0
System.out.println(str.charAt(0)); // Exception!

If you think about it, the initial value is not included. I can generate it, but there is no value in it. I had a dream that it contained data called an empty string. That wasn't the case. No, there is a character that is not the character "empty", but it is not a character even though the memory area is secured. Since the data as characters is "empty", the memory area is secured even if the length of the character string is 0. There is, but there is no such thing as the concept of "empty". It's profound. String.charAt () just stopped whispering StringIndexOutOfBoundsException. Alright, re-challenge.

String str = "I love you.";
System.out.println(str.length()); // 11
str = "I love you." + "";
System.out.println(str.length()); // 11

Yeah, the string length doesn't change. Of course. Because it is "empty". I suddenly returned to myself here. For example, Point p = new Point (); may be set with an initial value of 0 for both x and y because it is not a sequence.


The String class implements CharSequence, as does StringBuilder and StringBuffer. So, if they create an instance without giving anything to the argument, only the area to put the data is secured, and that is the characteristic of the array itself. It's a little different from String, but I didn't realize why I couldn't just generate it. I am writing this in agony. Collection is also different from an array, but first an instance of the framework itself such as List is created, and data is entered later. Even if it was an empty string, I wasn't relaxed that the string would be a string (some significant data). Why did you forget it? The foundation of the foundation is important, isn't it? I was keenly aware. At the same time, I felt the greatest disappointment for myself in this century.

Significance of initialization of a String type instance with an empty string

I think that initialization is to assign a value together with a declaration. Even if the data of a clear character string cannot be assigned, the information of an instance of String is generated and completed, so I think that initialization is initialization, but thanks to the wonderful concept of "empty", it is somehow. I feel that it contains some initialization complexity that other instances do not have. Well, since an empty string is a literal of a character string, it may be meaningful to have information that it is a character string type (String type), but I was convinced in the past. One of the meanings (I knew) of the empty string assignment of "reducing the possibility of exceptions caused by null" is not right now. Is it because Optional is now available? However, the usage is strange, such as Optional for instance initialization using string literals. I think Optional can be used nicely when the return value of a method is expected to be null. I don't feel thankful for such a place. On the contrary, it's just annoying. When using Eclipse, if you try to use a variable without initialization, you will get angry like a demon, and it seems useless to initialize with null or an empty string. I'm substituting an empty string with the feeling that it's unpleasant to just declare and not enter a value anymore. Null can be initialized, but it's null (nothing, no reference), so it feels like a crap. This is bad.

Always in the same way (2017-1-24 postscript)

@hiuchida commented that the fun of not having to separate null from non-null is wonderful. I will post the example as it is.

String empty = "";
for (char ch : empty.toCharArray()) {

Sure, it's tiring to always be aware of null or non-null. As you said, the point of view that you can enjoy yourself is also wonderful.

It was gudaguda, but I will leave it as it is as a commandment not to be caught again by the same "why?" Then, we set out on a journey to find a sound way to use the empty string.


What I swore to my heart

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