Java println(charArray + String) vs println(charArray)

Question

I have

char c1 = 'S';           // S as a character
char c2 = '\u0068';      // h in Unicode
char c3 = 0x0065;        // e in hexadecimal
char c4 = 0154;          // l in octal
char c5 = (char) 131170; // b, casted (131170-131072=121)
char c6 = (char) 131193; // y, casted (131193-131072=121)
char c7 = '\'';          // ' apostrophe special character
char c8 = 's';           // s as a character
char[] autoDesignerArray = {c1, c2, c3, c4, c5, c6, c7, c8};

And

System.out.println(autoDesignerArray + "Mustang");

Output: [C@c17164Mustang

System.out.println(autoDesignerArray);

Output: Shelby's

I'm not understanding why I get the weird output when I concatenate the char array with a string. What is the "[C@c17164"? The location in memory? And why do I get that when I concatenate with a string, but I get what I would expect when I print it alone?

System.out.println(autoDesignerArray + "Mustang"); and System.out.println(autoDesignerArray); are not the same method. System.out.println provide an overload that handle char array — ortis
– ortis, Commented Apr 2, 2015 at 14:16

Dandelion · Accepted Answer · 2015-04-03 09:55:00Z

7

The expression System.out.println(X + Y) is equal to the expression System.out.println(X.toString() + Y.toString()).

When you call System.out.println(autoDesignerArray + "Mustang") autoDesignerArray.toString() (which is "[C@c17164") is concatenated with "Mustang" and the result is printed.

edited Apr 3, 2015 at 9:55

Dandelion

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answered Apr 2, 2015 at 14:16

vahidreza

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2 Comments

Vikas Over a year ago

According to your 2nd point When you call System.out.println(autoDesignerArray) autoDesignerArray.toString() (which is "[C@c17164") should be printed but it prints Shelby's. Without String concatenation with array prints actual data but if we concatenate array with String then it prints hashcode address.

Pshemo Over a year ago

@VikasKumarSingh "According to your 2nd point When you call System.out.println(autoDesignerArray) autoDesignerArray.toString() (which is "[C@c17164") should be printed" not quite, autoDesignerArray.toString() returns string "[C@c17164", but println(autoDesignerArray) doesn't involve toString(), it simply prints each character from array. It is possible because in PrintStream (which System.out is instance of) exist few overloaded println methods, and one of them is println(char[]).

singhakash · Accepted Answer · 2015-04-02 14:40:28Z

2

Since every has array has a class the string you get is the object representation of its object i.e. [C@c17164Mustang where

[C is a class name ([ represent 1d array)
@ concates the the string
c17164 some hash code
Mustang your string

to check the class name of array do System.out.println(yourArray.getClass().getName());

For ex if you do System.out.println(new Object()); you will get something like java.lang.Object@25154f the string representation of object created.

And to print the actual values of array do System.out.println((java.util.Arrays.toString(autoDesignerArray))); which gives

[S, h, e, l, b, y, ', s]

Demo

edited Apr 2, 2015 at 14:40

answered Apr 2, 2015 at 14:25

singhakash

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1 Comment

Mike P Over a year ago

Thanks for explaining the other part of the question.

Crazyjavahacking · Accepted Answer · 2015-04-02 14:16:55Z

0

Arrays in java don't have overwritten toString() method, which means that:

System.out.println(autoDesignerArray + "Mustang");
- will print default toString() of array and concatenate it with the string
- the default implementation of toString() will print the binary name followed by hashCode() (char array will print [C followed by it's hash code)
System.out.println(autoDesignerArray);
- will actually call Arrays.toString() or similar functionality handling the toString() of arrays correctly

edited Apr 2, 2015 at 14:16

answered Apr 2, 2015 at 14:14

Crazyjavahacking

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1 Comment

npinti Over a year ago

I'm pretty sure that the 2nd point is due to this. Also not sure about the first one.

Community · Accepted Answer · 2017-05-23 11:45:58Z

0

This has to do with Arrays and why the fact that they don't implicitly inherit Object - For more information feel free to check out this SO question (have an answer there).

println(char[] s) does somewhat confuse me in the Oracle Doc - In C you would generally iterate through every element within the array and print each element follow by a \n to break the line.

However the jist of it all is that autoDesignerArray.toString() won't really work as you wish it would (Which is why it returns [C@c17164).

edited May 23, 2017 at 11:45

CommunityBot

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answered Apr 2, 2015 at 14:22

Juxhin

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