Scala Methods

Definitions 1. Method

grammar

def methodName (参数名:参数类型, 参数名:参数类型) : [return type] = {
    // 方法体：一系列的代码
}

Note item

• Parameter Type list can not be omitted
• Return type can be omitted, the compiler automatically inferred by the scala
• The return value can not write return, that is, the default value of the expression {} block

The sample code

//定义一个方法，实现两个整形数值相加，返回相加后的结果
//方式一
def add(a:Int,b:Int) : Int = {a + b}
//省略返回值的写法
def add(a:Int,b:Int)= {a + b}
//其它写法
def add(a:Int,b:Int) = a + b
//调用
add(1,2)

note

When defining the recursive method, the return type can not be omitted

The sample code

//定义递归方法（求阶乘）
//没有返回值写法 报错
def m2(x:Int) = {
	if(x<=1) 1
    else m2(x-1) * x
}

//有返回值写法,方法定义正确
def m2(x:Int):Int = {                                                                                                 | if(x<=1) 1                                                                                                            |     else m2(x-1) * x                                                                                                  | }   

2. The method parameters

Types of

1. The default parameters
2. With name parameter
3. Vararg

The default parameters

When defining the method can define a default value for parameter.

The sample code

// x，y的默认值为0 
//定义方法求两个数相加的值, 并且参数的的默认值为0
def add(x:Int = 0, y:Int = 0) = x + y
//调用
add();

With name parameter

When calling the method, you can specify the name of the parameter to make the call.

The sample code

def add(x:Int = 0, y:Int = 0) = x + y
add(x=1)

Vararg

If the parameters of the method is not fixed, a method may define the parameters is variable length parameter.

Syntax

//在参数类型后面加一个`*`号，表示参数可以是0个或者多个
def 方法名(参数名:参数类型*):返回值类型 = {
    方法体
}

The sample code

//1. 定义一个计算若干个值相加的方法
//2. 调用方法，传入以下数据：1,2,3,4,5
//  sum 求和
def add(num:Int*) = num.sum
//调用
add(1,2,3,4,5)

3. The method of calling

Called

1. Suffix call law
2. Infix call law
3. France braces call
4. Call the method without brackets

Suffix call law

Syntax

对象名.方法名(参数)

The sample code

Math.abs(-1)

Infix call law

grammar

对象名 方法名 参数

Note: The 如果有多个参数，使用括号括起来
code examples

Math abs -1

Method operator i.e.

The sample code

1 + 1

Explanation

In the scala, + - * /% of these operators and the like Java, but in the scala
all operators are methods
operator is a symbolic name of the method is a method

France braces call

Syntax
Note:方法只有一个参数，才能使用花括号调用法

Math.abs{ 
    // 表达式1
    // 表达式2
}

The sample code

Math.abs{-10}

Call the method without brackets

If the method has no parameters, names in brackets behind the method you can omit
the code sample

def m3()=println("hello")
m3