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I am learning Java this year as part of the AP Computer Science curriculum, and while I was reading about "Char" and "String" I could not understand why one would bother to use "Char" and only be able to store one character rather than just use "String" and be able to store much more than that. In short what's the point of "char" if it can only store a single character?
People are mentioning memory concerns, which are valid, but I don't think that's a very important reason 99% of the time. An important reason is that the Java compiler will tell you if you make a mistake so you don't have to figure it out on your own.
For example, if you only want 1 character for a variable, you can use a char to store the value and now nobody can put anything else in there without it being an error. If you used a String instead, there could be two characters in the String even though you intended that to never be possible. In fact, there could be 0 characters in the String which would be just as bad. Also, all your code that uses the String will have to say "get the first character of the String" where it could simply say, "give me the character".
An analogy (which may not make sense to you yet, unfortunately) would be, "Why would I say a Person has a Name when I could say a Person has a List of Names?" The same reasons apply. If you only want a Person to have one Name, then giving him a list of Names adds a lot maintenance overhead.
You could consider this analogy:
You need one apple. Would you prefer to have one apple in your hand, or a big box that could contain more apples, but only needs to contain the one?
The char primitive datatype is easier to work with than the String class in situations where you only need one character. It's also a lot less overhead, because the String class has a lot of extra methods and information that it needs to store to be efficient at handling string with multiple characters. Using the String class when you only need one character is basically overkill. If you want to read from a variable of both types to get the character, this is the code that would do that:
// initialization of the variables
char character = 'a';
String string = "a";
// writing a method that returns the character
char getChar()
{
return character; // simple!
}
char getCharFromString()
{
return string.charAt(0); // complicated, could fail if there is no character
}
If this code looks complicated, you can ignore it. The conclusion is that using String when you only need one character is overcomplicating things.
Basically, the String class is used when you need more than one character. You could also just create an array of chars, but then you would not have the useful methods of the String class, such as the .equals() and .length() methods.
Strings are objects. Objects always go on the dynamic storage. Storing one-character string would require at least a dozen of bytes.
chars (not Chars) are primitives. They take fixed amount of space (2 bytes). In situations when you need to process a single character, creating one-character string is a waste of resources. Moreover, when you expect to see a single character, using strings would require validation that the data passed in has exactly one character. This would be unacceptable in situations when you must be extremely fast, such as character-based input and output.
To summarize, you need a char because of
Memory footprint - a char is smaller than a String of one character
Speed of processing - creating objects carries an overhead
Program's maintainability - Knowing the type makes it easier for you and for the readers of your code to know what kind of data is expected to be stored in a char variable.
char take up less memory for times when you really only need one character. There are also multiple other applications for using a single character.
char is a primitive datatype while string is an object which comes at greater overhead.
A string is also made up of char, so there's that too.
Because the char takes up less memory!
Also the char is stored in memory and NOT as a reference value so theoretically its faster to access the char (You'll understand that more later)
***Note: I once had this same thought when I first started programming about why use an int when you can use a long and not have to worry about large numbers. This tells me you're on your way to be a great programmer! :)
char is a primitive type while String is a true Object. In some cases where performance is a concern it's conceivable that you would only want to use primitives.
Another case in which you would want to use char is when you're writing Java 1.0 and you're tasked with creating the String class!
public final class String
implements java.io.Serializable, Comparable<String>, CharSequence {
/** The value is used for character storage. */
private final char value[];
Everything in java can be reduced to primitive types. You can write any program with primitive types. So you need some kind of minimalist way of storing text. A char is also really just a byte, that is interpreted as a character.
Also if you want to loop though all characters in a string you would do:
char[] chArr = str.toCharArray();
for(int i = 0 ; i < chArr.length ; i++)
{
//do something with chArr[i];
}
This would be much more awkward trying to substring out an exact character from the String.
Lot of answers here already. While the memory concerns are valid, you have to realize there are times when you want to directly manipulate characters. The word ladder game
where you try to turn one word into another by changing one character at a time is an example I had to do in a programming class. Having a char type lets you manipulate a singe character at a time. It also lets you assign an int to a char that maps to your local character set.
You can do thing like char c = 97; and that will print out as a. You can do things like increment a character from 97 to 122 to print out all lowercase characters. Sometimes this actually is useful.
Related
Yes, I did check other threads and I have come to a conclusion. I just want you to confirm it so that I don't have any misconceptions.
Java String objects are not null terminated.
C++ std::string objects are also not null terminated
C strings or C-style strings if you will (array of characters), are the only strings that are null-terminated.
Correct or Incorrect?
C-strings are 0-terminated strings. You aren't forced to use them in C though.
Both C++ std::string and Java strings are counted strings, which means they store their length.
But C++ std::strings are also followed by a 0 since C++11, making them 0-terminated if (as often the case) they don't contain any embeddded 0, for better interoperability with 0-terminated-string APIs.
All of those are in themselves correct, but petty pedantery: C-style strings are not unique to C, there are other places where such things occur (most commonly in various forms of Assembler code, and C being a language originally designed to be "slightly above assembler" makes this "no surprise").
And in C++11, std::string is guaranteed to have a NUL terminator after the last actual string character [but it's valid to store NULL characters inside the string if you wish] (at least if you call c_str(), but in the implementations I've looked at, it's stored there on creation/update)
All the statements are not wrong, but need to clarify more of the specifics in each of the mentioned languages.
That is correct c++ std::string and java String both hold private fields indicating the length of the string. A NULL terminator is not needed.
The std::string method c_str returns the string as a NULL terminated char array for use when a NULL terminator is required e.g. c string functions such as strlen.
I don't know about the Java part, but in C++11 std::strings are NUL-terminated (besides storing the chars count), i.e. &s[0] returns the same string as s.c_str() (which is NUL-terminated, as a raw C-style string).
See this answer for more details.
The question you need to be asking is why C-String should be null terminated.
The answer is the string manipulation functions needs to know the exact length of the string. As strings in C are just array of characters there is no information that tells (this is the size of this array) they need something to help determining the size of array which is the null character standing at the end of it.
Where as in Java strings are instances of the String class which has the length field so there is no need for the null termination.
The same thing apply to strings in c++.
Almost correct.
C-string are not just an array of characters. They are a null-terminated array of characters.
So if you have an array of characters, it's not a C-string yet, it's just an ordinary array of characters. It has to have a terminating null character to be a valid C-style string.
Additionally, an std::string must also be null-terminated (since C++11). (But it still has a private variable holding the length of the string.)
Why is it that Java requires the char variable to enclose anything inside of it with single quotes rather than double? An example of this:
char s = 's'; //This will not break
vs:
char s = "s"; //This will break
I understand that double quotes are primarily for strings but is there a specific reason as to why chars were built to only use single quotes and to break when a double quote is entered?
I have tried to do some research but the only thing that was relevant was another SO Question, which refers to the difference between single and double quotes, not the reasoning behind the syntactical development of the char.
Because char and String are two different types, and how else is Java supposed to know whether you want a character or string of length 1?
For example, given the methods:
public void foo(String s) { }
public void foo(char c) { }
And the call
foo("a");
If characters could be made with double quotes, how would Java know which method to call?
This is a question written by a person used to the modern easy scripting languages whose goal is to make programming easy to learn and fast to type.
Java is a language for people who know what the CPU does underneath. In the world of low level languages (assembley, C, Java etc.) a character is an integer (UTF may require more than one int) whereas a string is an array of integers. By allowing a programmer to define the exact variable type, Java allows you to write more efficient code.
But it also allows you to write String s = "s"; if you don't care about efficiency.
I am currently reading a textbook on Java and each chapter involving the String datatype also discusses char. My question is, what purpose does char have in the real world?
The only thing I have found is that because String is immutable, it makes it a poor choice for passwords. Thus, one should choose a character array (char[]) over String. However, Java does have a mutable class for strings called StringBuilder; would that not be just as suitable a replacement for strings as is char[]?
This has already been answered in the comments really :)
A String is a collection of Chars. Without Chars you would have nothing to build Strings from.
Because Char[] and dealing with Char[] is so important they warrant having their own class to handle the processing of them - hence String.
In your coding you are unlikely to use the Char datatype directly unless you are processing Strings or handling passwords. The only reason Char[] is used for passwords is because it's harder to accidentally print them into logs/view them in memory/put them into string caches, etc and because once you have finished with it you can explicitly zero the elements in the Array so it never stays in memory longer than needed.
I want to know, if a String is a collection. I have read around but am still quite confused.
Strings are immutable objects representing a character sequence (CharSequence is one of the interfaces implemented by String).
Main difference to char arrays and collections of chars: String cannot be modified, it's not possible (ignoring reflection) to add/remove/replace characters.
Internally they are represented by a char array with an offset and length (this allows to create lightweight substrings, using the same char arrays).
Example: ['F','o','o','H','e','l','l','o',' ','W','o','r','l','d'], offset=3, count=5 = "Hello".
strings are object of class String and it's not a Collection as well. It is implemented on top of char array. You can see it in the below code snippet:
public final class String implements
java.io.Serializable, Comparable<String>, CharSequence
{
private final char value[];
No, it's not a collection in that it does not implement the Collection<E> interface.
Conceptually, it is an immutable sequence of characters (and implements the CharSequence interface).
Internally, the String class is likely to use an array of chars, although I am pretty sure the spec does not mandate that.
No, A string is an object of class String
The String class represents character strings. All string literals in
Java programs, such as "abc", are implemented as instances of this
class....
A String represents a string in the UTF-16 format in which
supplementary characters are represented by surrogate pairs (see the
section Unicode Character Representations in the Character class for
more information). Index values refer to char code units, so a
supplementary character uses two positions in a String.
No it's not an Array or a Collection. However there is a convenient method if you need a char array and you have a String - namely String.toCharArray(); you could use it like this
// Prints the String "Hello, World!" as a char[].
System.out.println(Arrays.toString("Hello, World!".toCharArray()));
No, a String is an immutable string of characters, and the class extends Object directly and does not implement any of the Collection interfaces. Really, that's the basic answer.
However, there's a lot going on under the covers in the runtime--there's a whole collection of cached strings held by the JVM and in its most primitive representation, yeah, a String is basically an array of characters (meaning it's a bunch of memory addresses pointing to representations of characters). Still, once you go below the definition of String as it's defined as a class, you can keep going until you get to the point that you're just talking about organized combinations of ones and zeroes.
I'm guessing here, but I imagine you posed the question because you're studying this and an instructor said something about a String being an array of characters. While technically correct, that's really confusing because the two concepts exists at completely different levels of abstraction.
String Class is just a class which allows you to create objects of strings. Like all classes it makes easy the use of these objects using its owns methods.
An array of char is an string, but its methods are relative to arrays or the elements of the array.
So for example if you want to look for the position of a carácter in an string of a class String then you use a method called IndexOf.
But if you want to find a character in an array of char, then you would have to do it manually using loops.
I've been set an assignment which requires me to capture the input of 5 strings, convert them to uppercase, output them as a string, convert them to their Unicode integers (using the getNumericValue method) and then manipulate the integers using some basic operators.
I get the first part but I am having trouble with the following:
Using the getNumericValue to convert
my single character literal strings
into their Unicode integer
counterparts.
Being able to assign these ints to
variables so I can further process s
them with operators, all the
examples I have seen have been
simple printing out the number and
not assigning it to a variable,
since I am a Java noob the syntax is
still a little confusing for me.
My code is here
If there is a cleaner way of doing what I want please suggest so but without the use of arrays or loops.
I don't understand why you don't want to do this without arrays or loops.
You can get the unicode values (as ints) making up the string via String.codePointAt(), or get the characters via charAt() followed by a getNumericValue() for each character. But regardless, you're going to have to iterate over the set of characters in the string via a loop, or perhaps recursion.
Yes, sounds like op needs to continue researching avenues of learning.
// difficult to code without interfering with
// instructor's prerogative
char ( array ) = String.getchars();
// Now what, unroll the loop?
...
As noted by Brian, loops are fundamental. I cannot imagine getChars being assigned before simple array techniques.