After a string literal, all the + will be treated as string concatenation operator why? [duplicate]

Answer 1

There are two kind of '+' operators in the statement, one of String object and one of Integer object:

String s = 10 + 30 +" Sachin " + 40 + 40;

The Operation that apply first is '10 + 30'. Let's look at the value of '10', this is interpreted to Integer object that activate the operator '+' on value '30' which results as Integer of 40.

The next operation is the last result 40 with ' Sachin ': 40 + ' Sachin '. Integer object that activate '+' operator on String object which results String object of '40 Sachin '.

The next operation is the last result String object ('40 Sachin ') that adds Integer 40 which results '40 Sachin 40'.

In the same manner the addition of the last '40', which finally results in '40 Sachin 4040'.

Answer 2

Because that's how it is implemented, because + is both used for adding numbers, as for String concatenation.

The first time, neither of the parts is a String, but both are numerical values that can be added, so it's used to add the values.

But, as soon as one part of the two is a String, it is used for String concatenation.

Change your code like this:

String s=10+30+" Sachin "+(40+40); 

Answer 3

This is because Java evaluates operands from left to right. Quoting section 15.7:

The Java programming language guarantees that the operands of operators appear to be evaluated in a specific evaluation order, namely, from left to right.

String s=10+30+" Sachin "+40+40;
//       ^^^^^ + the operands are of type int so int addition is performed
String s=40+" Sachin "+40+40;
//       ^^^^^^^^^^^^^ + the operands are of type int and String so String concatenation is performed
String s="40 Sachin "+40+40;
//       ^^^^^^^^^^^^^^^ + the operands are of type int and String so String concatenation is performed
String s="40 Sachin 40"+40;
//       ^^^^^^^^^^^^^^^^^ + the operands are of type int and String so String concatenation is performed
String s="40 Sachin 4040";

The behaviour of + when one of the operands is a String is specified in section 15.18.1 about the "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.

Answer 4

The expression is evaluated left to right. The first two operands are both int (10 and 30), so the first + performs addition.

The next + gets an int operand (40) and a String operand (" Sachin "), so it converts the int to String and performs String concatenation.

The next + operators get a String operand and an int operand, and also perform String concatenation.

If you want a different evaluation order, use parentheses :

String s=10+30+" Sachin "+(40+40);  

This will output 40 Sachin 80.

Answer 5

Addition is left associative. let's see it step by step

10+30+" Sachin "+40+40
-----           -------
40 +" Sachin "+40+40    <--- here both operands are integers with the + operator, which is addition
---
"40 Sachin "+40+40   <--- + operator on integer and string results in concatenation
-----------
"40 Sachin 40"+40   <--- + operator on integer and string results in concatenation
--------------
"40 Sachin 4040"   <--- + operator on integer and string results in concatenation
-----------------