网站意义学校,怎么做告白网站,网站建设福州,手机静态网站建设课程设计报告基本类型 声明变量 val#xff08;value的简写#xff09;用来声明一个不可变的变量#xff0c;这种变量在初始赋值之后就再也不能重新赋值#xff0c;对应Java中的final变量。 var#xff08;variable的简写#xff09;用来声明一个可变的变量#xff0c;这种变量在初始…基本类型 声明变量 valvalue的简写用来声明一个不可变的变量这种变量在初始赋值之后就再也不能重新赋值对应Java中的final变量。 varvariable的简写用来声明一个可变的变量这种变量在初始赋值之后仍然可以再被重新赋值对应Java中的非final变量。
类型自动推导
kotlin还能对我们的声明的变量进行类型的自动推导
易混淆的Long类型标记 Kotlin的数值类型转换 无符号类型
目的是为了兼容C
Kotlin的字符串 fun main() {var a 2val b Hello Kotlin// val c 12345678910l // compile error.val c 12345678910L // okval d 3.0 // Double, 3.0f Floatval e: Int 10//val f: Long e // implicitness not allowedval f: Long e.toLong() // implicitness not allowedval float1: Float 1fval double1 1.0val g: UInt 10uval h: ULong 100000000000000000uval i: UByte 1uprintln(Range of Int: [${Int.MIN_VALUE}, ${Int.MAX_VALUE}])println(Range of UInt: [${UInt.MIN_VALUE}, ${UInt.MAX_VALUE}])val j I❤️Chinaprintln(Value of String j is: $j) // no need bracketsprintln(Length of String j is: ${j.length}) // need bracketsSystem.out.printf(Length of String j is: %d\n, j.length)val k Today is a sunny day.val m String(Today is a sunny day..toCharArray())println(k m) // compare references.println(k m) // compare values.val n !doctype htmlhtmlheadmeta charsetUTF-8/titleHello World/title/headbodydiv idcontainerH1Hello World/H1pThis is a demo page./p/div/body/html.trimIndent()println(n)
}public class JavaBasicTypes {public static void main(String... args) {int a 2;final String b Hello Java;long c 12345678910l; // ok but not good.long d 12345678910L; // okint e 10;long f e; // implicit conversion// no unsigned numbers.String j I❤️China;System.out.println(Value of String j is: j);System.out.println(Length of String j is: j.length());System.out.printf(Length of String j is: %d\n, j.length());String k Today is a sunny day.;String m new String(Today is a sunny day.);System.out.println(k m); // compare references.System.out.println(k.equals(m)); // compare values.String n !doctype html\n html\n head\n meta charset\UTF-8\/\n titleHello World/title\n /head\n body\n div id\container\\n H1Hello World/H1\n pThis is a demo page./p\n /div\n /body\n /html;System.out.println(n);}
}
数组Array 数组的创建 数组的长度 数组的读写 数组的遍历 数组的包含关系 fun main() {val a IntArray(5)println(a.size) //same with the Collections(e.g. List)val b ArrayListString()println(b.size)val c0 intArrayOf(1, 2, 3, 4, 5)val c1 IntArray(5){ 3 * (it 1) } // y 3*(x 1)println(c1.contentToString())val d arrayOf(Hello, World)d[1] Kotlinprintln(${d[0]}, ${d[1]})val e floatArrayOf(1f, 3f, 5f, 7f)for (element in e) {println(element)}e.forEach {println(it)}if(1f in e){println(1f exists in variable e)}if(1.2f !in e){println(1.2f not exists in variable e)}}import java.util.ArrayList;public class JavaArrays {public static void main(String... args) {int[] a new int[5];System.out.println(a.length);// only array use lengthArrayListString b new ArrayList();System.out.println(b.size());int[] c new int[]{1, 2, 3, 4, 5};String[] d new String[]{Hello, World};d[1] Java;System.out.println(d[0] , d[1]);float[] e new float[]{1, 3, 5, 7};for (float element : e) {System.out.println(element);}for (int i 0; i e.length; i) {System.out.println(e[i]);}// Test in an Arrayfor (float element : e) {if(element 1f){System.out.println(1f exists in variable e);break;}}//Test not in an Arrayboolean exists false;for (float element : e) {if(element 1.2f){exists true;break;}}if(!exists){System.out.println(1.2f not exists in variable e);}}
}
区间
区间的创建
闭区间 开区间 倒序区间 区间的步长 区间的迭代 区间的包含关系 区间的应用 fun main() {val intRange 1..10 // [1, 10]val charRange a..zval longRange 1L..100Lval floatRange 1f .. 2f // [1, 2]val doubleRange 1.0 .. 2.0println(intRange.joinToString())println(floatRange.toString())val uintRange 1U..10Uval ulongRange 1UL..10ULval intRangeWithStep 1..10 step 2val charRangeWithStep a..z step 2val longRangeWithStep 1L..100L step 5println(intRangeWithStep.joinToString())val intRangeExclusive 1 until 10 // [1, 10)val charRangeExclusive a until zval longRangeExclusive 1L until 100Lprintln(intRangeExclusive.joinToString())val intRangeReverse 10 downTo 1 // [10, 9, ... , 1]val charRangeReverse z downTo aval longRangeReverse 100L downTo 1Lprintln(intRangeReverse.joinToString())for (element in intRange) {println(element)}intRange.forEach {println(it)}if (3.0 !in doubleRange) {println(3 in range intRange)}if (12 !in intRange) {println(12 not in range intRange)}val array intArrayOf(1, 3, 5, 7)for (i in 0 until array.size) {println(array[i])}for(i in array.indices){println(array[i])}
}集合框架 集合框架的接口类型对比 集合框架的创建 集合实现类复用与类型别名 集合框架的读写和修改 Pair Triple fun main() {val intList: ListInt listOf(1, 2, 3, 4)val intList2: MutableListInt mutableListOf(1, 2, 3, 4)val map: MapString, Any mapOf(name to benny, age to 20)val map2: MapString, Any mutableMapOf(name to benny, age to 20)val stringList ArrayListString()for (i in 0 .. 10){stringList.add(num: $i)}for (i in 0 .. 10){stringList num: $i}for (i in 0 .. 10){stringList - num: $i}stringList[5] HelloWorldval valueAt5 stringList[5]val hashMap HashMapString, Int()hashMap[Hello] 10println(hashMap[Hello])// val pair Hello to Kotlin
// val pair Pair(Hello, Kotlin)
//
// val first pair.first
// val second pair.second
// val (x, y) pairval triple Triple(x, 2, 3.0)val first triple.firstval second triple.secondval third triple.thirdval (x, y, z) triple}import java.util.*;public class JavaCollections {public static void main(String... args) {ListInteger intList new ArrayList(Arrays.asList(1, 2, 3, 4));ListString stringList new ArrayList();for (int i 0; i 10; i) {stringList.add(num: i);}for (int i 0; i 10; i) {stringList.remove(num: i);}stringList.set(5, HelloWorld);String valueAt5 stringList.get(5);HashMapString, Integer hashMap new HashMap();hashMap.put(Hello, 10);System.out.println(hashMap.get(Hello));}
}
函数
有自己的类型可以赋值、传递并再合适的条件下调用
函数的定义 函数vs方法 函数的类型 函数的引用
函数的引用类似C语言的函数指针可用于函数传递 由于类型可以自动推断所以可以不用写类型名
变长参数 多返回值 默认参数 具名参数 package com.bennyhuo.kotlin.builtintypes.functionsfun main(vararg args: String) {println(args.contentToString())val x:(Foo, String, Long)-Any Foo::barval x0: Function3Foo, String, Long, Any Foo::bar// (Foo, String, Long)-Any Foo.(String, Long)-Any Function3Foo, String, Long, Anyval y: (Foo, String, Long) - Any xval z: Function3Foo, String, Long, Any xyy(x)val f: ()-Unit ::fooval g: (Int) -String ::fooval h: (Foo, String, Long)-Any Foo::barmultiParameters(1, 2, 3, 4)defaultParameter(y Hello)val (a, b, c) multiReturnValues() //伪val r a bval r1 a c}fun yy(p: (Foo, String, Long) - Any){//p(Foo(), Hello, 3L)
}class Foo {fun bar(p0: String, p1: Long): Any{ TODO() }
}fun foo() { }
fun foo(p0: Int): String { TODO() }fun defaultParameter(x: Int 5, y: String, z: Long 0L){TODO()
}fun multiParameters(vararg ints: Int){println(ints.contentToString())
}fun multiReturnValues(): TripleInt, Long, Double {return Triple(1, 3L, 4.0)
}
案例四则计算器
/*** input: 3 * 4*/
fun main(vararg args: String) {if(args.size 3){return showHelp()}val operators mapOf( to ::plus,- to ::minus,* to ::times,/ to ::div)val op args[1]val opFunc operators[op] ?: return showHelp()try {println(Input: ${args.joinToString( )})println(Output: ${opFunc(args[0].toInt(), args[2].toInt())})} catch (e: Exception) {println(Invalid Arguments.)showHelp()}
}fun plus(arg0: Int, arg1: Int): Int{return arg0 arg1
}fun minus(arg0: Int, arg1: Int): Int{return arg0 - arg1
}fun times(arg0: Int, arg1: Int): Int{return arg0 * arg1
}fun div(arg0: Int, arg1: Int): Int{return arg0 / arg1
}fun showHelp(){println(Simple Calculator:Input: 3 * 4Output: 12.trimIndent())
}
