java operator precedence DOT vs logical AND

Question

if(fName != null && fName.isEmpty())

In this if expression we have 4 operators

1) . access object member
2) () invoke a method
3) != equality
4) && conditional AND

I have listed as per precedence and all have same associativity i.e left to right

Then why this expression evaluate in order below (to my knowledge)

1) !=
2) &&
3,4) . ()

I just want to know why compiler evaluates in a order against the precedency — Amit Yadav, Oct 09 '15 at 08:36
Possible duplicate of [What are the rules for evaluation order in Java?](http://stackoverflow.com/questions/6800590/what-are-the-rules-for-evaluation-order-in-java) — Andy Turner, Oct 09 '15 at 08:38
it start to evaluate from () because of only that ur expression going to read by compiler. — Pankaj Saboo, Oct 09 '15 at 08:46

Eran · Answer 1 · 2015-10-09T08:52:59.577

A logical AND operator (&&) is short circuited. It means the right operand is only evaluated if the left operand evaluates to true.

Therefore fName != null is evaluated first.

If it's true, fName.isEmpty() is evaluated next, and finally the && operator itself is evaluated, since you can't evaluate it before you evaluate its operands.

Here are relevant quotes from the JLS :

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.

15.7.1 :

The left-hand operand of a binary operator appears to be fully evaluated before any part of the right-hand operand is evaluated.

15.7.2 :

The Java programming language guarantees that every operand of an operator (except the conditional operators &&, ||, and ? :) appears to be fully evaluated before any part of the operation itself is performed.

.@Eran but && is having less precedence over . and () then why it evaluate first? — Amit Yadav, Oct 09 '15 at 08:35
@AmitYadav The && operator has two operands - the left is `fName != null` and the right is `fName.isEmpty()`. — Eran, Oct 09 '15 at 09:08

score 0 · Answer 2 · answered Oct 09 '15 at 08:50

In Java, operands are evaluated left to right. So the !=, being part of the left operand of &&, and having higher priority, is evaluated first.
The && operator doesn't evaluate its right operand if its left operand is false.

The operator associativity you posted has nothing to do with it.

java operator precedence DOT vs logical AND

2 Answers2