Kotlin中"it"和"this"关键字的区别

1. Introduction

Kotlin offers a rich set of features to make our code expressive and readable. Two of the frequently used keywords in Kotlin, it and this, may appear to be quite similar at first glance. However, understanding the differences between them can greatly enhance our programming skills and help us write more maintainable code.

In this tutorial, we’ll discuss the differences between the it and this keywords in Kotlin, and their use cases in different contexts.

2. The it Keyword in Kotlin

Kotlin uses the it keyword as an implicit name for single-parameter lambda expressions or anonymous functions. It simplifies the syntax for these expressions by eliminating the need to explicitly declare a name for that parameter:

fun addOne(numbers: List<Int>): List<Int> {
    return numbers.map{ it + 1 }
}

In this code, we have a function called addOne() that takes a list of integer numbers as a parameter and returns a new list of integers. The map() function performs the transformation. In the map() function, we have a lambda expression where we use it to represent each element of the numbers list as we iterate over it. So, the lambda adds one to each element of the numbers list.

Let’s take a look at how we can test our code with JUnit:

@Test
fun testAddOne() {
    val inputNumbers = listOf(1, 2, 3, 4, 5)
    val result = addOne(inputNumbers)
    val expected = listOf(2, 3, 4, 5, 6)
    assertEquals(expected, result)
}