StringBuildier

[Kamila Bertran]

Bit confused here on output.
So I create this StringBuilder object:

new StringBuilder(10 + 2 + "SUN" + 4 + 5);

The output is 12SUN45. Why not 12SUN9?

[Jeanne Boyarsky]

Kamila,
Good question. Java sees the String "SUN" in the expression. Which means it says "lets use String concatenation for the + operator. If you wanted the 9, you'd need to use parenthesis.

[Ganish Patil]

10 + 2 + "SUN" + 4 + 5

Evaluation starts from left side.

Steps:

10 + Now it looks at right side to check, is there any high precedence operator than +? answer is no so (All are additive operators so same precedence so left associative)

( 10 + 2 ) result = 12

12 + again it looks at right side to check, is there any high precedence operator than +? answer is no so

( 12 + "SUN" )
Explanation:
String conversion is performed because one operand is String i.e. "SUN" so 12 whose default primitive type is int is converted to Integer like new Integer(12); then this reference value is converted to type String by String conversion. Concatination of String using + operator uses StringBuilder's append method to append them and then converts to String using toString method of StringBuilder.
Now result =  "12SUN"

( "12SUN" + 4 )  same like above String conversion process result = "12SUN4"

( "12SUN4" + 5 ) same like above String conversion process result = "12SUN45"

Final result = "12SUN45"

Edit: Then at last passes this String to parameterized constructor of StringBuilder i.e  public StringBuilder(String str)

[Kamila Bertran]

so the moment there's change of type StringBuldier just 'switches' to that new type? Therefore as 10 and 2 are int it just sums it up, but than goes 'hey, I can't add 'SUN' to that, let's trat the rest as a String' ??

[Kamila Bertran]

Ganish Patil wrote:

10 + 2 + "SUN" + 4 + 5

Evaluation starts from left side.

(...)

That was awesome. Couldn't get a better explanation! Thanks for taking your time!

[Ganish Patil]

You're welcome