increments order in java

Question

Why in java this code outputs 1:

int bracketsTest = 0;
int resultBrackets = 1 + bracketsTest + bracketsTest++; // return 1

But this outputs 2:

int bracketsTest = 0;
int resultBrackets = 1 + bracketsTest++ + bracketsTest; // return 2

I lived in the world where both snippets should be equal, since in both results we do the following:

1. 1 + 0 + bracketsTest // bracketsTest = 0 and we put zero in bracketsTest++, after that bracketsTest = 1
   
2. 1 + 0 + 1 = 2 // we put bracketsTest = 1 in last argument
   but turns out that increment/decrement operation is not highest prioritet operations? (since it is matter where we put bracketsTest in code snippet)

Answer 1

Evaluation order

You seem to mix operator precendence with evaluation order. Please have a look at JLS§15.7. Evaluation Order:

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

Also:

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.

Additionally:

The Java programming language respects the order of evaluation indicated explicitly by parentheses and implicitly by operator precedence.

But that part only plays a role once you perform the operation itself. Before that happens, all operands will already be fully evaluated.

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First snippet

Knowing that, we can decipher what is going on. The first snippet:

1 + bracketsTest + bracketsTest++

Will first of all evaluate all the operands (from left to right), so we get:

1. operand: 1
2. operand: 0
3. operand: 0 (and increment bracketsTest)

While evaluationg the third operand, it will increment bracketsTest. Now, it will add everything together and we get 1 + 0 + 0 = 1 as result.

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Second snippet

The second snippet:

1 + bracketsTest++ + bracketsTest;

is evaluated from left to right as well, so we have:

1. operand: 1
2. operand: 0 (and increment bracketsTest)
3. operand: 1 (because it was just incremented)

Hence we receive 1 + 0 + 1 = 2.