Understanding Scala if, if...else, and Nested Conditional Statements

if Statement

In Scala, an if statement consists of a Boolean expression followed by a block of code that is executed when the expression evaluates to true.

Syntax

if (BooleanExpression) {
    // code executed when the expression is true
}

Example

object Test {
    def main(args: Array[String]) {
        var x = 10;
        if (x < 20) {
            println("x < 20")
        }
    }
}

Running the code produces:

$ scalac Test.scala
$ scala Test
x < 20

if...else Statement

An if statement can be followed by an else block, which is executed when the Boolean expression is false.

Syntax

if (BooleanExpression) {
    // code executed when true
} else {
    // code executed when false
}

Example

object Test {
    def main(args: Array[String]) {
        var x = 30;
        if (x < 20) {
            println("x 小于 20")
        } else {
            println("x 大于 20")
        }
    }
}

Running the code produces:

$ scalac Test.scala
$ scala Test
x 大于 20

if...else if...else Statement

Multiple conditions can be chained using else if, allowing the program to select the first true condition among several.

Syntax

if (BooleanExpression1) {
    // code for true condition 1
} else if (BooleanExpression2) {
    // code for true condition 2
} else if (BooleanExpression3) {
    // code for true condition 3
} else {
    // code when all conditions are false
}

Example

object Test {
    def main(args: Array[String]) {
        var x = 30;
        if (x == 10) {
            println("X 的值为 10")
        } else if (x == 20) {
            println("X 的值为 20")
        } else if (x == 30) {
            println("X 的值为 30")
        } else {
            println("无法判断 X 的值")
        }
    }
}

Running the code produces:

$ scalac Test.scala
$ scala Test
X 的值为 30

Nested if...else Statements

Conditional statements can be nested, allowing an if block to contain another if statement.

Syntax

if (BooleanExpression1) {
    // code for true condition 1
    if (BooleanExpression2) {
        // code for true condition 2
    }
}

Example

object Test {
    def main(args: Array[String]) {
        var x = 30;
        var y = 10;
        if (x == 30) {
            if (y == 10) {
                println("X = 30 , Y = 10")
            }
        }
    }
}

Running the code produces:

$ scalac Test.scala
$ scala Test
X = 30 , Y = 10