7. 基本文法(プリミティブ型(基本データ型)はありません。 )
var intVariable: Int = 0
var floatVariable: Float = 0f
var doubleVariable: Double = 0.0
var longVariable: Long = 0L
var shortVariable: Short = 0
var byteVariable: Byte = 0
var booleanVariable: Boolean = false
// 型推論を使う場合
var intVariable = 0
var floatVariable = 0f
var doubleVariable = 0.0
var longVariable = 0L
var booleanVariable = false
int intVariable = 0;
float floatVariable = 0;
double doubleVariable = 0;
long longVariable = 0;
short shortVariable = 0;
byte byteVariable = 0;
boolean booleanVariable = false;
Kotlin Java
9. 基本文法(引数にデフォルト値が設定できます。 )
class ClassA {
public void methodA() {
methodA("a", "b", "c");
}
public void methodA(String arg1) {
methodA(arg1, "b", "c");
}
public void methodA(String arg1, String arg2) {
methodA(arg1, arg2, "c");
}
public void methodA(String arg1, String arg2, String arg3) {
System.out.println(arg1 + " " + arg2 + " " + arg3);
}
public void methodA2(String arg2) {
System.out.println("a" + " " + arg2 + " " + "c");
}
public void main() {
methodA(); // a b c
methodA("d"); // d b c
methodA("d", "e"); // d e c
methodA("d", "e", "f"); // d e f
methodA2("g"); // a g c
}
}
Kotlin Java
class ClassA {
fun methodA(arg1: String = "a", arg2: String = "b", arg3: String = "c"){
print("${arg1} ${arg2} ${arg3}")
}
fun main() {
methodA() // a b c
methodA("d") // d b c
methodA("d", "e") // d e c
methodA("d", "e", "f") // d e f
methodA(arg2 = "g") // a g c
}
}
}
10. 基本文法(引数にデフォルト値が設定できます。 )
class ClassA {
private String arg1 = "";
public ClassA() {
this("a");
}
public ClassA(String arg1) {
this.arg1 = arg1;
}
public String getArg1() {
return arg1;
}
public void setArg1(String arg1) {
this.arg1 = arg1;
}
}
Kotlin Java
class ClassA(var arg1: String = "a")
class ClassA(arg1: String = "a") {
var arg1 = arg1
}
class ClassA(arg1: String = "a") {
var arg1 = arg1
set(value) {
field = value
}
get() {
return arg1
}
}
11. 基本文法(三項演算子はありません。 )
fun test(a: Int): Int {
return if (a >= 1) {
100
} else {
999
}
}
public int test(int a) {
return a >= 1 ? 100 : 999;
}
Kotlin Java
13. val array = arrayOf(1, 2, 3)
val intArray = intArrayOf(1, 2, 3) // floatArrayOf, charArrayOf, booleanArrayOf etc...
val blankArray: Array<Int?> = arrayOfNulls(10) // nullのから配列:要素数10個
val list = listOf("a", "b", "c") // List<String>
val mutableList = mutableListOf("a", "b", "c") // ArrayList<String>
val map = mapOf("a" to 1, "b" to 2, "c" to 3) // Map<K, V>
val map2 = mapOf<String, Int>("a" to 1, "b" to 2, "c" to 3)
val mutableMap = mutableMapOf("a" to 1, "b" to 2, "c" to 3)
val set = setOf(1, 2, 3)
val mutableSet = mutableSetOf(1, 2, 3)
配列、コレクション(関数をつかった宣言方法 )
Kotlin
14. 配列、コレクション(Stream API相当の実装)
val array = listOf("aaaa", "bbbb", "cccc")
val count = array.filter { it == "aaaa" }.count()
ArrayList<String> array = new ArrayList<>();
array.add("aaaa");
array.add("bbbb");
array.add("cccc");
Long count = array.stream()
.filter(s -> s.equals("aaaa")).count();
Kotlin Java