I was experimenting with toCharArray() and found some strange behavior.
Suppose private static final char[] HEX_CHARS = "0123456789abcdef".toCharArray();
System.out.println(HEX_CHARS);
/* prints 0123456789abcdef */
System.out.println("this is HEX_CHARS "+HEX_CHARS);
/* prints [C#19821f */
Any theoretical reason behind this?
It is because the parameter to println is different in the two calls.
The first parameter is called with char[] and the second is called with a string, where HEX_CHARS is converted with a call to .toString().
The println() have an overriden method that accepts a charArray.
The first line calls the method
print(char[] s)
on the PrintStream which prints what you expect. The second one calls the method
print(String s)
Where is concatenating the string with the toString implementation of the array which is that ugly thing you get ([C#19821f).
Arrays are objects, and its toString methods returns
getClass().getName() + "#" + Integer.toHexString(hashCode())
In your case [C#19821f means char[] and #19821f is its hashcode in hex notation.
If you want to print values from that array use iteration or Arrays.toString method.
`System.out.println(Arrays.toString(HEX_CHARS));`
The strange output is the toString() of the char[] type. for some odd reason, java decided to have a useless default implementation of toString() on array types. try Arrays.toString(HEX_STRING) instead.
Related
I wanted to create a char array of the alphabet. I looked at this post:
Better way to generate array of all letters in the alphabet
which said this:
char[] alphabet = "abcdefghijklmnopqrstuvwxyz".toCharArray();
So in my code I have:
public class Alphabet {
private char[] letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
public String availableLetters(){
return letters.toString();
}
}
When I call the function availableLetters() from main() and printit to the console, it outputs this garbage:
[C#15db9742
What am I doing wrong?
The array is correct, the problem is that you are not printing it correctly.
If you print your array one character at a time, you would get a correct result:
for (char c : letters) {
System.out.print("'" + c + "' ");
}
demo
Unfortunately, Java standard class library does not provide a meaningful override of toString() for arrays, causing a lot of trouble for programmers who are new to the language.
If you want to print it in array form, then use:
System.out.println(Arrays.toString(letters));
BTW: The [C#15db9742 is not really garbage. It's what gets printed out when a class does not override the toString() method.
From Object.toString():
Returns a string representation of the object. In general, the
toString method returns a string that "textually represents" this
object. The result should be a concise but informative representation
that is easy for a person to read. It is recommended that all
subclasses override this method. The toString method for class Object
returns a string consisting of the name of the class of which the
object is an instance, the at-sign character `#', and the unsigned
hexadecimal representation of the hash code of the object. In other
words, this method returns a string equal to the value of:
getClass().getName() + '#' + Integer.toHexString(hashCode())
You can pass the char array to the String constructor or the static method String.valueOf() and return that instead.
I am a bit confused about the StringBuilder. It seems that when I print a StringBuilder, there it no need to add .toString() because it will automatically give me a string representation. However, when I return a StringBuilder object, I have to add the .toString(). Is that true? and why?
Also, I am bit confused about the following code:
package com.tutorialspoint;
import java.lang.*;
public class StringBuilderDemo {
public static void main(String[] args) {
StringBuilder str = new StringBuilder("India ");
System.out.println("string = " + str);
// append character to the StringBuilder
str.append('!');
// convert to string object and print it
System.out.println("After append = " + str.toString());
str = new StringBuilder("Hi ");
System.out.println("string = " + str);
// append integer to the StringBuilder
str.append(123);
// convert to string object and print it
System.out.println("After append = " + str.toString());
}
}
For the different println, sometimes this code use toString and some other times it didn't. Why? I tried deleting the toString and the results are the same. Is it still necessary to use toString in println?
Thanks so much for helping a newbie out!
When you print an object to a print stream, the String representation of that object will be printed, hence toString is invoked.
Some classes override Object#toString, amongst which StringBuilder does.
Hence explicitly invoking toString for StringBuilder is unnecessary.
On the other hand, other objects don't override toString. For instance, arrays.
When you print an array, unless using a utility such as Arrays.toString, you're getting the array's class type # its hash code, as opposed to a human-readable representation of its contents.
From the documentation:
Note that println() prints a string builder, as in:
System.out.println(sb);
because sb.toString() is called implicitly, as it is with any other object in a println() invocation.
If you try to append an object to a string like this : "string = " + str, the toString() method is implicitly called.
So no, it does not matter, if you specify it.
Also the toString() method itself (even when you are not append it to string) calls the toString() method.
Therefore System.out.println(str) and System.out.println(str.toString()) gives same result.
The first thing you should know about Java is that we work with objects and that all objects inherit methods from the class Object: http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html
This class has a toString() method and since every object inherits this method it can always be called on every object. When you do not override it, it usually returns the physical address of the object.
Like stated in other answers, whenever a string is expected in println for instance and you pass an object it automatically calls the method which requires an Object (note the capital, we are talking about the class Object here), it will then use the toString method on the object passed along as parameter. The reason you get the string you want is because StringBuilder overrides the toString() method for you.
When you in your own code want to pass the string in your StringBuilder you have two options. You can either pass StringBuilder.toString() or change the return type to Object or StringBuilder and call toString() when you actually need it.
Hope this clarifies why you can just pass the object instead of the string.
I was experimenting with toCharArray() and found some strange behavior.
Suppose private static final char[] HEX_CHARS = "0123456789abcdef".toCharArray();
System.out.println(HEX_CHARS);
/* prints 0123456789abcdef */
System.out.println("this is HEX_CHARS "+HEX_CHARS);
/* prints [C#19821f */
Any theoretical reason behind this?
It is because the parameter to println is different in the two calls.
The first parameter is called with char[] and the second is called with a string, where HEX_CHARS is converted with a call to .toString().
The println() have an overriden method that accepts a charArray.
The first line calls the method
print(char[] s)
on the PrintStream which prints what you expect. The second one calls the method
print(String s)
Where is concatenating the string with the toString implementation of the array which is that ugly thing you get ([C#19821f).
Arrays are objects, and its toString methods returns
getClass().getName() + "#" + Integer.toHexString(hashCode())
In your case [C#19821f means char[] and #19821f is its hashcode in hex notation.
If you want to print values from that array use iteration or Arrays.toString method.
`System.out.println(Arrays.toString(HEX_CHARS));`
The strange output is the toString() of the char[] type. for some odd reason, java decided to have a useless default implementation of toString() on array types. try Arrays.toString(HEX_STRING) instead.
This question already has answers here:
Why does the toString method in java not seem to work for an array
(9 answers)
How to convert a char array back to a string?
(14 answers)
Closed 9 years ago.
I thought the toString method will make a char array to a String, but I was wrong.
char[] k=new char[2];
k[0]='k';
k[1]='k';
System.out.println(k.toString());
This code will output: [C#112f614.
What exactly happened in this code k.toString()?
Should I never call toString method in a char array?
Thanks!
Happy New Year!
You want to use Arrays.toString(char[]{'a','b'});
You can use
char data[] = {'a', 'b', 'c'};
String str = new String(data);
See the javadoc
public String(char[] value)
Allocates a new String so that it
represents the sequence of characters currently contained in the
character array argument. The contents of the character array are
copied; subsequent modification of the character array does not affect
the newly created string. Parameters: value - The initial value of the
string
http://docs.oracle.com/javase/6/docs/api/java/lang/String.html
Calling toString on an array will call the toString method from Object. Which will return you the hashCode
public String toString() Returns a string representation of the
object. In general, the toString method returns a string that
"textually represents" this object. The result should be a concise but
informative representation that is easy for a person to read. It is
recommended that all subclasses override this method. The toString
method for class Object returns a string consisting of the name of the
class of which the object is an instance, the at-sign character `#',
and the unsigned hexadecimal representation of the hash code of the
object. In other words, this method returns a string equal to the
value of:
getClass().getName() + '#' + Integer.toHexString(hashCode())
Returns: a string representation of the object.
Because arrays are objects. So calling toString() result to call the toString() method herited from the object class which is :
public String toString() {
return getClass().getName() + "#" + Integer.toHexString(hashCode());
}
In [C#112f614, [C means that it's an array of char.
If you want to print the content of your array, use Arrays.toString(char[] a)
What exactly happened in this code k.toString()? Should I never call toString method in a char array?
The toString method of a char array inherits the default toString behavior from Object, which is to simply print a unique identifier derived from the object's location in memory. So unless you want that unique identifier, there's not much point in calling k.toString(). (k being your char array)
You should likely never call toString on any sort of array. The Arrays class has many utility methods for creating string representations of arrays.
A partial answer to this question: "What exactly happened in this code k.toString()?"
toString() is inherited from java.lang.Object and not overridden. The implementation just print the canonical class name plus the #-letter plus the hashcode. That is all. Therefore calling this methode is not useful for applications and is just for debugging purposes in IDEs to at least enlighten which type of object is there.
String can take a char array as a constructor.
String s = new String(k);
I had used the following code to find the length
String str=strLenData.toString();
int ipLen= str.length();
return ipLen;
ipLen would return 11 every time. whatever be the actual value of strLenData. when I call toString() function, value of str: "[C#40523f80". Now I have to use char[] and i need to know the end (or length) of char[].
How do I do it?
If I understand correctly the strLenData variable is a char[]? In that case, you can just do
return strLenData.length;.
I don't think strLenData is charSequence or something. its just a regular object and may be it does't have toString() method. so toString() method of Object class gets called which just returns the HashCode value of The Objects Reference.
so make sure strLenData.toString() can be used.
ipLen is returning 11 always because you are converting an char array to String equivalent by using toString() method.
if you want to create String by an char array use.
String str = new String(strLenData);
Or if you want just want to get length of your char array use answer given by Steven.
use strLenData.length;