*EL Operators*S2C Home **«** *EL Operators*

Symbols used for mathematical and logical manipulation that are recognized by the compiler are commonly known as operators in Java and with EL we also have a comprehensive, although reduced, list of operators. In
this lesson we look at the arithmetic, relational, logical, conditional and `empty`

EL operators we can use within our JSP pages.

### Arithmetic Operators Top

We are familiar with most of the *arithmetic operators* in the table below from everyday life and they generally work in the same way in EL.

Operator | Meaning | Example | Notes |
---|---|---|---|

+ | Addition | `${a + b}` | |

`-` | Subtraction | `${a - b}` | |

`/` `div` | Division | `${a / b}` | Any remainder will be truncated. |

`*` | Multiplication | `${a * b}` | |

`%` `mod` | Modulus | `${a % b}` | Holds the remainder value of a division. |

### Relational Operators Top

Relational Operators refer to the relationships that values can have to each other. Relational Operators produce a `true`

or `false`

result. Any type can be compared for equality or inequality
but only types that support an *ordering* relationship can be applied for comparison. The table below clarifies this where `a = 5`

and `b = 5`

Operator | Meaning | Example | Result | Notes |
---|---|---|---|---|

`==` `eq` | Equal to | `${a == b}` | `true` | All types can be compared for equality |

`!=` `ne` | Not Equal to | `${a != b}` | `false` | All types can be compared for inequality |

`<` `lt` | Less than | `${a < b}` | `false` | Can be used with all numeric types and the `char` type. |

`<=` `le` | Less than or equal to | `${a <= b}` | `true` | Can be used with all numeric types and the `char` type. |

`>` `gt` | Greater than | `${a > b}` | `false` | Can be used with all numeric types and the `char` type. |

`>=` `ge` | Greater than or equal to | `${a >= b}` | `true` | Can be used with all numeric types and the `char` type. |

### Logical Operators Top

Logical Operands must be the `Boolean`

type and the result of a logical operation is the `Boolean`

type and are used with control statements. The following table shows all possible combinations and their result.

Operator | Meaning | Example | Result | Notes |
---|---|---|---|---|

`&&` | Short-circuit `AND` | Boolean a = false; Boolean b = false;`${a && b}` Boolean a = false; Boolean b = true; `${a && b}` Boolean a = true; Boolean b = false; `${a && b}` Boolean a = true; Boolean b = true; `${a && b}` |
`false` `false` `false` `true` | If the first operand returns `false` , the second operand will not be checked (short-circuited) and `false` is returned. |

`||` | Short-circuit `OR` | Boolean a = false; Boolean b = false;`${a || b}` Boolean a = false; Boolean b = true; `${a || b}` Boolean a = true; Boolean b = false; `${a || b}` Boolean a = true; Boolean b = true; `${a || b}` |
`false` `true` `true` `true` | If the first operand returns `true` , the second operand will not be checked (short-circuited) and `true` is returned. |

`!` | `NOT` | Boolean a = false;`${!a}` Boolean a = true; `${!a}` |
`true` `false` | Will check if operand is not `true` . |

### The Conditional Operator Top

The Conditional operatotor is tenary (takes three operands) and can be used to replace an `if....else`

construct of the following form:

Construct | Description |
---|---|

`if....else` | |

`if (condition) { ` | Assign result of `expression1` to
var if `condition` evaluates to `true` ,otherwise assign result of `expression2` to var. |

The Conditional Operator | |

`${statement? expression1 : expression2 ` |
If `statement` evaluates to `true` evaluate `expression1` ,
otherwise evaluate `expression2` , |

The following code snippet shows how to use the `Conditional`

operator which for this code will result in `higher number`

being output:

```
```**<%
request.setAttribute("a", 15);
request.setAttribute("b", 6);
%>
${(requestScope.a lt requestScope.b)? "lower number" : "higher number"}**

### The `empty`

Operator Top

The `empty`

operator can be used to test the emptiness of an object and has the following syntax:

```
```**${empty obj}**

The `empty`

operator will return `true`

when any of the following criteria is met, otherwise it will return `false`

:

- If the object being tested is
`null`

. - If the object being tested is an empty string (
`""`

). - If the object being tested is an empty array.
- If the object being tested is an empty Map or Collection.

### Operator Precedence Top

The table below shows the order of precedence that is invoked when the container interprets EL operator symbols, including the reserved word operators. When using multiple operators in an expression it is always best practice to use parentheses to explicitly state the order of precedence for clarity and readability. The table lists order of precedence from highest to lowest.

Precedence | Operators | Operation | Associativity |
---|---|---|---|

1 | `!` | boolean logical NOT | right |

`not` | |||

2 | `empty` | left | |

3 | `/` | division | left |

`div` | |||

`*` | multiplication | ||

`%` | modulus | ||

`mod` | |||

4 | `+` | addition or string concatenation | left |

`-` | subtraction | ||

5 | `<` | less than | left |

`lt` | |||

`<=` | less than or equal to | ||

`le` | |||

`>` | greater than | ||

`gt` | |||

`>=` | greater than or equal to | ||

`ge` | |||

`instanceof` | reference test | ||

6 | `==` | equal to | left |

`eq` | |||

`!-` | not equal to | ||

`ne` | |||

7 | `&&` | short-cricuit boolean logical AND | left |

`and` | |||

8 | `||` | short-cricuit boolean logical OR | left |

`or` |

## Lesson 2 Complete

In this lesson we learnt about the symbols used in EL for mathematical and logical manipulation which are known as EL operators.

### What's Next?

In the next lesson we learn how to use EL to access object properties and attribute values from any scope.