Arithmetic, relational, increment

Arithmetic operators: + - * / % with the precedence you expect (*, /, % bind tighter than +, -), left to right among equals.

System.out.println(2 + 3 * 4);      // 14, not 20
System.out.println((2 + 3) * 4);    // 20 — parentheses win
System.out.println(10 - 4 - 3);     // 3  — left to right

Relational operators produce a boolean: < > <= >= == !=.

int x = 5;
System.out.println(x < 10);     // true
System.out.println(x == 5);     // true — == compares values
System.out.println(x != 5);     // false

The single = assigns; the double == compares. if (x = 5) does not even compile in Java (an int is not a boolean) — a lucky protection.

Increment and decrement:

int n = 5;
n++;        // n is 6 (statement form: same as n = n + 1)
n--;        // n is 5

As a statement (the AP-exam form), n++ and ++n are identical. Only inside a larger expression do ++n (increment then use) and n++ (use then increment) differ — a distinction the exam tests by asking what a statement sequence prints, so trace one statement at a time.