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

Answer 1

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.