Basic types
See https://kotlinlang.org/docs/basic-types.html
Note String.length and Array.size. Both of them have count(), i.e.,
String.count() and Array.count().
String.isNotBlank() and String.isNotEmpty().
String.isBlank() and String.isEmpty() returns true for an empty string "".
Differences between Array<Float> and FloatArray:
Array<Float>stores objects
FloatArrayis a primitive array
Array<Float>toFloatArray:.toFloatArray()
FloatArraytoArray<Float>:.toTypedArray()
- ranges:
start..end:[start, end]start until end:[start, end)
kotlinc -include-runtime -d hello.jar hello.kt
./code/basic-types/hello.kt
fun testInt() {
val a = 1
check(a is Int)
check(a == 1)
val b = 1L
check(b is Long)
check(b == 1L)
val c :Byte = -1
check(c is Byte)
check(c == (-1).toByte())
val d: Short = 1
check(d is Short)
check(d == 1.toShort())
val g = 0x0a
check(g is Int)
check(g == 10)
val f = 0b00001000
check(f is Int)
check(f == 8)
val h = 0b0000_1000
check(h is Int)
check(h == 8)
val k = 1_000
check(k is Int)
check(k == 1000)
val m = 1 / 2
check(m is Int)
check(m == 0)
val n = 1 / 2.toFloat()
check(n is Float)
check(n == 0.5f)
}
fun testFloat() {
val a = 1.0
check(a is Double)
check(a == 1.0)
val b = 2.0F
check(b is Float)
check(b == 2.0F)
check(b == (2.0).toFloat())
// either f or F is ok
val c = 2.0f
check(c is Float)
check(c == 2.0F)
val d = (2.2F).toInt()
check(d is Int)
check(d == 2)
}
fun testBitwise() {
// support only Int and Long
val a = 0b01
val b = 0b10
val c = a or b // in C++: c = a | b
check(c == 3)
val d = a and b // in C++: d = a & b
check(d == 0)
val f = a shl 3 // in C++: a << 3
check(f == 8)
val g = b shr 1 // in C++: g = b >> 1
check(g == 1)
val h = a xor b // in C++: h = a ^ b
check(h == 3)
val k :Byte = 0b0100_0001
// test inv()
}
fun testJavaClass() {
val a = 1
println(a.javaClass) // int
}
fun testBoolean() {
val a = true
val b = false
val c: Boolean = true
check(a)
check(!b)
check(c)
val d = a && b
check(d == false)
val e = a || b
check(e)
}
fun testChar() {
// a char is 2-byte, utf-16
val a = 'a'
check(a is Char)
check(a.isDigit() == false)
check(a.isLetter() == true)
val b = '\uff00'
check(b is Char)
val c = '9'
check(c.isDigit() == true)
check(c.isLetter() == false)
check(Char.SIZE_BITS == 16)
check('0'.code == 0x30)
check('A'.lowercaseChar() == 'a')
check('a'.uppercaseChar() == 'A')
}
// note String is immutable, like Python.
fun testString() {
// a sequence of Char, utf16
// immutable
val a = "Abc"
check(a + 1 == "Abc1")
check(a.count() == 3)
check(a.length == 3)
check(a.lastIndex == a.length - 1)
check(a.uppercase() == "ABC")
check(a.lowercase() == "abc")
// remove the first two characters
check(a.drop(2) == "c")
// remove the last two characters
check(a.dropLast(2) == "A")
check(a.indexOf("bc") == 1)
// multi-line strings, like python
val b = """
line 1
line 2
"""
println(b)
/*
line 1
line 2
*/
val c = """
|line 1
|line 2
""".trimMargin()
println(c)
/*
line 1
line 2
*/
val d = """
>line 1
>line 2
""".trimMargin(">")
println(d)
/*
line 1
line 2
*/
// format
val k = String.format("%x %02x", 10, 10)
check(k == "a 0a")
}
fun testArray() {
val a = Array(3) {it}
check(a[0] == 0)
check(a[1] == 1)
check(a[2] == 2)
// val b = arrayOf(0, 1, 2)
val b = arrayOf<Int>(0, 1, 2)
check(a.contentEquals(b)) // we cannot use == since they save references
a[0] = 10 // assign a value
check(a[0] == 10)
check(a.sum() == 10 + 1 + 2)
check(a.joinToString() == "10, 1, 2")
}
fun shortArrayToByteArray() {
val a: Array<Short> = arrayOf(0x0102, 0x0304)
val b: Array<Byte> = Array(a.size * 2) {0}
println(a.contentToString()) // [258, 772]
println(b.contentToString()) // [0, 0, 0, 0]
for (i in a.indices) {
b[2*i] = (a[i].toInt() and 0xff).toByte()
b[2*i+1] =((a[i].toInt() shr 8) and 0xff).toByte()
}
println(b.contentToString()) // [2, 1, 4, 3]
}
fun byteArrayToShortArray() {
val a: Array<Byte> = arrayOf(0x01, 0x02, 0x03, 0x04)
val b: Array<Short> = Array(a.size / 2) {0}
println(a.contentToString()) // [258, 772]
println(b.contentToString()) // [0, 0, 0, 0]
for (i in b.indices) {
b[i] = (a[2*i].toInt() + (a[2*i+1].toInt() shl 8)).toShort()
}
check(b[0].toInt() == 0x0201)
check(b[1].toInt() == 0x0403)
}
fun main() {
testInt()
testFloat()
testBitwise()
testJavaClass()
testBoolean()
testChar()
testString()
testArray()
shortArrayToByteArray()
byteArrayToShortArray()
}
CharSequence
It is an interface.