<pre>
classMainTestActivity : Activity() {
//当某个变量的值可以为null的时候，必须在声明处的类型后添加?来标识该引用可为空。
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.main_test_activity)
kotlin_test.setText("kotlin测试")
valtestButton= findViewById(R.id.kotlin_test_btn) as Button
testButton.setText("进行kotlin测试")
testButton.setOnClickListener {
Toast.makeText(this,"kotlin点击事件",Toast.LENGTH_LONG).show()
}
//变量声明：
//可以用关键字var声明为可变的，否则使用只读关键字val
//一次赋值（只读）的局部变量:
//int类型常量定义
val aConstant: Int =1000
val bConstant: Int =200
val cConstant: Int =300
//可变变量：
var dVariable: Int
dVariable=5
Log.d("alen","sum is " + sum(aConstant,bConstant))
Log.d("alen","printSum is " + printSum(aConstant,bConstant,cConstant))
stringTemplate()
printValue("4","6")
printValue("4","")
val length= getStringLength("nihao")
Log.d("alen","length is " +length)
loopForTest1()
loopForTest2()
whileForTest()
Log.d("alen","msg is " + whenForTest("hello"))
Log.d("alen","msg is " + whenForTest(1))
mapForTest()
setForDataClassTest()}
}
}
//使用字符串模板
fun stringTemplate(): Unit {
var arg: Int =1
val s1= "arg is$arg"
Log.d("alen","s1 is " +s1)
arg=2
//模板中的任意表达式：
var s2= "${s1.replace("is","was")}, but now arg is$arg"
Log.d("alen","s2 is " +s2)
}// 带有两个Int参数、返回Int的函数
funsum(arg1: Int,arg2: Int): Int {
returnarg1 + arg2
}// 函数返回无意义的值,Unit返回类型可以省略
funprintSum(arg1: Int,arg2: Int,arg3: Int): Unit {
Log.d("alen","sum is " + (arg1 + arg2 + arg3))
}// 把字符串转为Int
fun parseInt(str: String): Int? {
// try表达式
try{
if(str !=null) {
returnstr.toInt()
}
} catch (e: NumberFormatException) {
return null}return null
}
}
funprintValue(str1: String,str2: String) {
val result1: Int? = parseInt(str1)
valr esult2: Int? = parseInt(str2)
if(result1!=null&&result2!=null) {
Log.d("alen","value is " +result1*result2)
} else {
Log.d("alen"," '$result1' or '$result2' is null")
}
}// 打印字符串的长度
fun getStringLength(obj: Any): Int? {
if(obj is String) {
return obj.length
}
return null
}
// 迭代
fun loopForTest1() {
val items=listOf("item1","item2","item3")
for(item in items) {
Log.d("alen","item is " +item);
}
}
// 通过索引值进行循环
fun loopForTest2() {
val items=listOf("item1","item2","item3")
//使用in运算符来检测某个数字是否在指定区间内：
for(index in items.indices) {
Log.d("alen","item index is$index,value is${items[index]}")
}
if(-1 !in items.indices) {
Log.d("alen","-1 not in range")
}
// 从9到0开始迭代，步长为3
// 区间表达式由具有操作符形式..的rangeTo函数辅以in和!in形成。
// downTo()函数 倒序迭代数字
// step()函数 以不等于1的任意步长迭代数字
for(x in 9 downTo 0 step 3) {
Log.d("alen","x is " +x)
}
//创建一个不包括其结束元素的区间，可以使用until函数：
for(x in 1 until 10) {
// i in [1, 10)排除了10
Log.d("alen","until x is " +x)
}
}// while循环测试
fun whileForTest() {
val items=listOf("apple","item2","banana")
items.isEmpty()
Log.d("alen","items size is " +items.size)
//区间range
Log.d("alen","items indices is " +items.indices)
if(items.size >2) {
Log.d("alen","items index 2 is " +items.get(2))
}
Log.d("alen","items last index is " +items.lastIndex)
//使用in运算符来判断集合内是否包含某实例：
when {
"apple"initems-> {
Log.d("alen","items contain apple")
}
"orange"!initems-> {
Log.d("alen","items do not contain orange")
}
}
}
// when条件测试
fun whenForTest(obj: Any): String =
when(obj) {
1-> {
Log.d("alen","test one")
"one"
}
"hello" -> "Greeting"
isLong -> "Long"
!isString -> "Not a string"
else-> "Unkonwn"
}// map测试
fun mapForTest() {
val map=mapOf("a"to"1","b"to"2","c"to"3")
Log.d("alen","map key is a,value is " +map["a"])
for(item in map) {
Log.d("alen","map key is " +item.key + ",value is " +item.value)
}
}
// set测试
// set
// 1. Set中没有重复的对象
// 2. Set中对象不按特定的方式排序
//判断两个对象的是否重复标准是hashCode()和equals()两个参考值，
//也就是说只有两个对象的hashCode值一样与equals()为真时，才认为是相同的对象
// fun hashSetOf(vararg elements: T): java.util.HashSet
// fun linkedSetOf(vararg elements: T): java.util.LinkedHashSet
// sortedSetOf(comparator: java.util.Comparator, vararg elements: T): java.util.TreeSet
// fun sortedSetOf(vararg elements: T): java.util.TreeSet
funsetForDataClassTest() {
// Book是一个data class，用来做data model使用
val bookA= Book("A",20,"AA")
val bookB= Book("B",30,"BB")
val bookC= Book("C",20,"CC")
val bookD= Book("D",50,"DD")
val bookE= Book("B",30,"EE")
val set=setOf(bookA,bookB,bookC,bookD)
for(iteminset) {
Log.d("alen","item$item, hashCode${item.hashCode()}")
}
Log.d("alen","--------------------------")
val mutalbeSet=mutableSetOf(bookA,bookB,bookC,bookD,bookE)
for(item in mutalbeSet) {
Log.d("alen","item is$item, hashCode is${item.hashCode()}")
}
mutalbeSet.add(Book("甲乙丙丁",50,"EE"))
Log.d("alen","remove B value is " +mutalbeSet.remove(bookB))
Log.d("alen","remove E value is " +mutalbeSet.remove(bookE))
Log.d("alen","--------------------------")
for(item in mutalbeSet) {
Log.d("alen","item is$item, hashCode is${item.hashCode()}")
}
}</pre>
