Question

When assigments are happening right to left,why following doesn’t give compiler error?

String str = str = "";

Answer 1

The behaviour is defined by the Java Lanaguage Specification #15.1 about the assignment operator. Namely (emphasis mine):

Otherwise, three steps are required:

• First, the left-hand operand is evaluated to produce a variable. If this evaluation completes abruptly, then the assignment expression completes abruptly for the same reason; the right-hand operand is not evaluated and no assignment occurs.
• Otherwise, the right-hand operand is evaluated. If this evaluation completes abruptly, then the assignment expression completes abruptly for the same reason and no assignment occurs.
• Otherwise, the value of the right-hand operand is converted to the type of the left-hand variable, is subjected to value set conversion (§5.1.13) to the appropriate standard value set (not an extended-exponent value set), and the result of the conversion is stored into the variable.

So the evaluation of the expression str = str = ""; is from right to left, but the left-hand operand String str is evaluated first and creates the variable.