Difference between '.' and "." in java

Question

Hi

Is there a difference between concatenating strings with '' and ""?

For example, what is the difference between:

String s = "hello" + "/" + "world";

and

String s = "hello" + '/' + "world";

Thanks in advance.

Answer 1

"." is a String, '.' is a char.

Answer 2

Literals enclosed in double quotes, e.g. "foo", are strings, whereas single-quoted literals, e.g. 'c', are chars. In terms of concatenation behaviour, there'll be no discernible difference.

Nevertheless, it's worth remembering that strings and chars aren't interchangeable in all scenarios, and you can't have a single-quoted string made up of multiple characters.

Answer 3

"." is a String consisting of only one character. '.' is a character.

Once you concatenate them together there is no difference.

Answer 4

Theoretically it is quicker to add a char to a string - Java 6 seems to create StringBuffers under the covers and I remember reading on a Java Performance site that concatenating a char will be marginally quicker.

Answer 5

'' is for character literals.

So you cannot do this:

"Osc" + 'ar' + "Reyes"

Because ar is not a character literal.

In your example it doesn't make much difference because

'/'

is a char literal, and

 "/"

is a String literal containing only one character.

Additionally you can use any UTF character with the following syntax

'\u3c00'

So you can also use:

"Osc" + '\u3c00' + "ar

Answer 6

Adding a char is about 25% faster than adding a one character String. Often this doesn't matter however, for example

String s = "hello" + "/" + "world";

This is converted to one String by the compiler so no String concatenation/append will occur at run-time in any case.

Answer 7

You will probably find the following articles useful:

• Java String Performance Testing
• Java String Concatenation

Answer 8

System.out.println('a'+'b'+'c');
> 294
System.out.println("a"+"b"+"c");
> abc

What's happening here is that (char)+(char)=(int) In other words. Use "" for text to avoid surprises.

Answer 9

You may just look into the JDK :-)

Given two functions:

public static String concatString(String cs) {
    return "hello" + cs + "world";
}

public static String concatChar(char cc) {
    return "hello" + cc + "world";
}

after examination of the bytecode it boils down to two AbstractStringBuilder.append(String) vs. AbstractStringBuilder.append(char).

Both methods invoke AbstractStringBuilder.expandCapacity(int)) which will allocate a new char[] eventually and System.arraycopy the old content first.

Afterwards AbstractStringBuilder.append(char) just has to put the given char in the array whereas AbstractStringBuilder.append(String) has to check a few constraints and calls String.getChars(int, int, char[], int) which does another System.arraycopy of the appended string.