Android Kotlin(八) 运算符重载

首先申明下，本文为笔者学习《Kotlin 程序开发入门精要》的笔记，并加入笔者自己的理解和归纳总结。

Kotlin允许我们对数据类型的一组预定义的操作符提供实现函数。

1. 一元操作符重载

表达式	对应的函数
+a	a.unaryPlus()
-a	a.unaryMinus()
!a	a.not()
a++	a.inc()
a–	a.dec()

我们假设一个复数类Complex，有实部real和虚部imag

class Complex(r: Int, i: Int) {
    var real = r
    var imag = i

    override fun toString(): String {
        if (imag >= 0) {
            return "$real +${imag}i"
        } else {
            return "$real ${imag}i"
        }
    }

}

函数重载inc()和dec()

operator fun Complex.inc() = Complex(real + 1, imag + 1)

operator fun Complex.dec() = Complex(real - 1, imag - 1)

fun main(args: Array) {
    var comp1 = Complex(5, -10)	

    println(comp1++)  // 5 -10i
    println(++comp1)  // 7 -8i
}

2. 二元操作符重载

表达式	对应的函数
a + b	a.plus(b)
a - b	a.minus(b)
a * b	a.times(b)
a / b	a.div(b)
a % b	a.mod(b)
a…b	a.rangeTo(b)
a in b	b.contains(a)
a !in b	!b.contains(a)

函数重载plus()和minus()

operator fun Complex.plus(other: Complex) = Complex(real + other.real, imag + other.imag)

operator fun Complex.minus(other: Complex) = Complex(real - other.real, imag - other.imag)

fun main(args: Array) {
    var comp1 = Complex(8, -10)
    var comp2 = Complex(5, 5)

    println(comp1 + comp2)  // 13 -5i
    println(comp1 - comp2)  // 3 -15i
}

3. 方括号操作符重载

表达式	对应的函数
a[i]	a.get(i)
a[i, j]	a.get(i, j)
a[i] = b	a.set(i, b)
a[i, j] = b	a.set(i, j, b)

函数重载get()和set()方法

class StringList {
    var list = mutableListOf("Hello World!", "Welcome")

    operator fun get(i: Int): String {
        return list[i]
    }

    operator fun set(i: Int, value: String) {
        list[i] = value
    }

    operator fun get(i: Int, j: Int): Char {
        return list[i][j]
    }

}

fun main(args: Array) {
    var list = StringList()

    println(list[0])  // Hello World!
    println(list[1, 5])  // m

    list[0] = "Hi Mike"
    println(list[0])  // Hi Mike
}

4. 赋值操作符重载

表达式	对应的函数
a+=b	a.plusAssign(b)
a-=b	a.minusAssign(b)
a*=b	a.timesAssign(b)
a/=b	a.divAssign(b)
a%=b	a.modAssign(b)

函数重载timesAssign()方法

operator fun Complex.timesAssign(n: Int) {
    real *= n
    imag *= n
}

fun main(args: Array) {
    var comp = Complex(5, -10)	
    comp *= 5
    println(comp)  // 25 -50i
}

5. 逻辑操作符重载

表达式	对应的函数
a>b	a.compareTo(b)>0
a	a.compareTo(b)<0
a>=b	a.compareTo(b)>=0
a<=b	a.compareTo(b)<=0
a==b	a?.equals(b) ?: b===null
a!=b	!(a?.equals(b) ?: b===null)

函数重载equals()方法，必须在Complex内部实现

operator override fun equals(other: Any?): Boolean {
    if (other is Complex) {
        return real == other.real && imag == other.imag
    }
    return false
}

函数重载compareTo()方法

operator fun Complex.compareTo(other: Complex): Int {
    var diff = real - other.real
    return if (diff != 0) diff else imag - other.imag
}

fun main(args: Array) {
    var comp1 = Complex(5, 10)	
    var comp2 = Complex(8, -6)
    var comp3 = Complex(8, -6)

    println(comp1 > comp2)  // false
    println(comp2 <= comp3)  // true

    println(comp1 == comp2)  // false
    println(comp2 == comp3)  // true
}