EXPRESSIONS

String Concatenation Operator

+

15.17.1

15.17   Additive Operators

The operators

+

 and

 are called the

additive operators

. They have the same pre 

cedence and are syntactically left associative (they group left to right).

AdditiveExpression:

MultiplicativeExpression

AdditiveExpression

 +

MultiplicativeExpression

AdditiveExpression

MultiplicativeExpression

If the type of either operand of a + operator is

String

, then the operation is

string concatenation.

Otherwise, the type of each of the operands of the

+

 operator must be a primi 

tive numeric type, or a compile time error occurs.

In every case, the type of each of the operands of the binary

 operator must

be a primitive numeric type, or a compile time error occurs.

15.17.1   String Concatenation Operator

+

If only one operand expression is of type

String

, then string conversion is per 

formed on the other operand to produce a string at run time. The result is a refer 

ence to a newly created

String

 object that is the concatenation of the two

operand strings. The characters of the left hand operand precede the characters of

the right hand operand in the newly created string.

15.17.1.1

String Conversion

Any type may be converted to type

String

 by

string conversion

.

A value

x

 of primitive type

T

 is first converted to a reference value as if by

giving it as an argument to an appropriate class instance creation expression:

If

T

 is

boolean

, then use

new Boolean(x)

 ( 20.4).

If

T

 is

char

, then use

new Character(x)

 ( 20.5).

If

T

 is

byte

,

short

, or

int

, then use

new Integer(x)

 ( 20.7).

If

T

 is

long

, then use

new Long(x)

 ( 20.8).

If

T

 is

float

, then use

new Float(x)

 ( 20.9).

If

T

 is

double

, then use

new Double(x)

 ( 20.10).

This reference value is then converted to type

String

 by string conversion.

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