Java operator overloading with strings+characters

Question

I'have doubt,if im asking wrong please correct me Question is

        String s="hello";
        String s1=' ';//error
        String s2=s+' ';

I know line1 is correct and line 2 is wrong because we can initialize char a= ' '; but am confused in line3 i read + operator in java can be used for concatenation with strings but it accepts characters like ' ' what is the reason ?

Similar to doing s + 5, it's casted to String. For non-primitives, toString() will be called — Vince
– Vince, Commented Dec 10, 2014 at 5:05
Side note: If s is a String and a and b are integers, be careful with something like s + a + b. This is not the same as s + (a + b). The first one converts each integer to a string and appends the strings in turn. The second one adds the integers first. — ajb
– ajb, Commented Dec 10, 2014 at 5:12

Thilo · Accepted Answer · 2014-12-10 05:05:33Z

4

The + operator is heavily overloaded. It takes almost anything.

If either side is a String, then the other will be converted to a String. That works with char as well as for other primitive types. For Objects, toString() is called (after a null-check).

answered Dec 10, 2014 at 5:05

Thilo

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2 Comments

J.K Over a year ago

please explain this too String s2=s+''; is error String s2=s+' '; is works fine String s2=s+'a'; is works

ajb Over a year ago

@jenuine It looks like your first example has two single quote marks, i.e. String s2 = s + ''? This just isn't legal syntax. Single quote marks are used for character literals, and you can't have a character literal with no characters. (Or with 2 or more characters.) The Java compiler will not accept '' anywhere.

Evgeniy Dorofeev · Accepted Answer · 2014-12-10 05:07:03Z

2

JLS 15.18.1. String Concatenation Operator +

If only one operand expression is of type String, then string conversion (§5.1.11) is performed on the other operand to produce a string at run time.

answered Dec 10, 2014 at 5:07

Evgeniy Dorofeev

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Community · Accepted Answer · 2020-06-20 09:12:55Z

1

JLS 5.4 String Conversion says,

String conversion applies only to an operand of the binary + operator which is not a String when the other operand is a String.

In this single special case, the non-String operand to the + is converted to a String (§5.1.11) and evaluation of the + operator proceeds as specified in §15.18.1.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Dec 10, 2014 at 5:08

Elliott Frisch

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