It’s essential to know how Java interprets the symbols you use to perform specific operations and in what order it interprets them. Otherwise, you could write an application with one result in mind and receive an entirely different result. Whenever you have a doubt as to how Java will interpret a symbol you use, you can rely on the information in this table to help you.
| Priority | Operators | Description | Associativity |
|---|---|---|---|
| 1 | [] | Array index used to specify which array element to access. | Left |
| 1 | () | Method call or grouping. Grouping is especially important in that it changes the normal rules for interacting with operators, such as performing addition before multiplication. | Left |
| 1 | . | Member access used to interact with a member of an object. | Left |
| 2 | ++ | Prefix or postfix increment. Adds a value of 1 to the variable. | Right |
| 2 | -- | Prefix or postfix decrement. Removes a value of 1 from the variable. | Right |
| 2 | + - |
Unary plus or minus. Sets the sign of the variable. The plus operator is never used because variables are positive by default. The minus operator negates the variable. | Right |
| 2 | ~ | Unary bitwise Not operator reverses the bits in a variable. In other words, it makes the variable the opposite of what it was. For example, a 5 (binary 00000101) becomes a –6 (binary 11111010). | Right |
| 2 | ! | Unary Boolean Not operator is used in Boolean evaluations to turn true into false and false into true. | Right |
| 2 | (type) | Performs a cast to change the type of a variable into another type. | Right |
| 2 | new | Creates a new object based on the class provided. | Right |
| 3 | * / % |
Performs the multiplication, division, and remainder math operations. | Left |
| 4 | + - |
Performs the addition and subtraction math operations. | Left |
| 4 | + | Concatenates two strings to produce a single string. | Left |
| 5 |
>> >>> |
Bitwise shift operators that are rarely used for application development. A discussion of these operators is beyond the scope of this book. | Left |
| 6 | Performs the logical comparison of two values for less than or less than and equal to. | Left | |
| 6 | > >= |
Performs the logical comparison of two values for greater than or greater than and equal to. | Left |
| 6 | instanceof | Tests whether an object is an instance of a particular class. | Left |
| 7 | == | Determines whether two values are precisely equal. | Left |
| 7 | != | Determines whether two values are not equal. | Left |
| 8 | & | Bitwise AND operation that combines two values. A discussion of this operator is outside the scope of this book. | Left |
| 8 | & | Logical AND operation that combines the results of two logical evaluations. In many cases, both condition A and condition B must be true in order for an entire evaluation to be true. | Left |
| 9 | ^ | Bitwise exclusive or (XOR) operation that combines two values. A discussion of this operator is outside the scope of this book. | Left |
| 9 | ^ | Logical XOR operation that combines the result of two logical evaluations. In order to be true, either condition A or condition B must be true, but not both. | Left |
| 10 | | | Bitwise OR operation that combines two values. A discussion of this operator is outside the scope of this book. | Left |
| 10 | | | Logical OR operation that combines the result of two logical evaluations. In order to be true, condition A or condition B, or both must be true. | Left |
| 11 | && | Logical AND operation that’s used as part of a logical expression to determine the truth value of both expressions. Both must be true for the entire expression to be true. | Left |
| 12 | || | Logical OR operation that’s used as part of a logical expression to determine the truth value of both expressions. Either or both must be true for the entire expression to be true. | Left |
| 13 | ? : | Performs a conditional assessment. See the “Using Relational and Conditional Operators” section of this chapter for details. | Right |
| 14 | = | Assigns the specified value to the variable. | Right |
| 14 | *= /= += -= %= >= >>>= &= ^= |= |
Combined operation and assignment. Java performs the requested
operation, such as addition, and then assigns the result to the
variable. The combined assignment operators include a number of operators that perform bitwise operations. A discussion of these operators is outside the scope of this book. |
Right |
The Priority column is probably the most important because it defines the strict order in which Java interprets the symbols displayed in the Operators column. An operator higher in the table always takes precedence over an operator that’s lower in the table.
The Associativity column is also important. In most cases, Java interprets symbols from left to right, which means that the symbols have a left associativity. However, in a few cases, the operator works from right to left.
For example, when using the = operator, Java interprets the information to the right of the operator first, and it then assigns the result to the operand on the left of the operator. So the flow is from right to left, which makes the = operator right associative.
Associativity is a math term that defines how elements in a binary operation interact. In most cases, Java uses left associativity. It begins from the left side of a group of operators and works toward the right side.
For example, if you have 1 + 2 + 3 as an equation, Java adds 1 and 2 first, then adds 3 to the result of the first operation. You can control associativity by using parenthesis. The article at Math.com provides more information on this topic.
