Java
int pos = 1;
for (Item item : items) {
log(pos, item);
pos++;
}
Kotlin 変換直後
var pos = 1
for (item in items) {
log(pos, item)
pos++
}
forEachIndexed 使用
items.forEachIndexed { index, item -> log(index + 1, item)}
2017年8月24日木曜日
Kotlin メモ : forEachIndexed
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/for-each-indexed.html
Java
Java
2017年8月22日火曜日
Kotlin メモ : mapNotNull
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/map-not-null.html
val list = (0 until adapter.count)
.map { adapter.item(it) }
.filterNotNull()
.toList()
mapNotNull 使用
val list = (0 until adapter.count)
.mapNotNull { adapter.item(it) }
.toList()
Kotlin メモ : until
https://kotlinlang.org/docs/reference/ranges.html
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.ranges/until.html
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.ranges/until.html
val list = (0..adapter.count - 1)
.map { adapter.item(it) }
.filterNotNull()
.toList()
until 使用
val list = (0 until adapter.count)
.map { adapter.item(it) }
.filterNotNull()
.toList()
Kotlin メモ : filterNotNull
filterNotNull
Java
Java
final List<Item> list = new ArrayList<>();
for (int i = 0, count = adapter.getCount(); i < count; i++) {
final Item item = adapter.getItem(i);
if (item != null) {
list.add(item);
}
}
Kotlin 自動変換直後
val list = ArrayList<Item>()
var i = 0
val count = adapter.count
while (i < count) {
val item = adapter.item(i)
if (item != null) {
list.add(item)
}
i++
}
range, let 使用
val list = ArrayList<Item>()
for(i in 0..adapter.count - 1) {
adapter.item(i)?.let {
list.add(it)
}
}
map, filterNotNull 使用
val list = (0..adapter.count - 1)
.map { adapter.item(it) }
.filterNotNull()
.toList()
2017年8月16日水曜日
Kotlin メモ : indexOfFirst
indexOfFirst
predicate にマッチする最初の位置の index を返す。マッチするものが無い場合は -1 を返す。
Java
predicate にマッチする最初の位置の index を返す。マッチするものが無い場合は -1 を返す。
Java
@Override
public int getSectionForPosition(int position) {
final Object[] sections = getSections();
if (sections == null) {
return 0;
}
int section = 0;
for (int i = 0; i < sections.length; i++) {
final MonthSection ms = (MonthSection) sections[i];
if (ms.position > position) {
return section;
}
section = i;
}
return section;
}
Kotlin
override fun getSectionForPosition(position: Int): Int {
val sections = getSections() ?: return 0
return sections.indexOfFirst { it.position > position }
.let {
when {
it > 0 -> it - 1
it == 0 -> 0
else -> sections.lastIndex
}
}
}
2017年8月10日木曜日
Kotlin メモ : ArrayAdapter
Java
class MyAdapter extends ArrayAdapter<MyData> {
private final LayoutInflater inflater;
MyAdapter(Context context, List<MyData> objects) {
super(context, 0, objects);
inflater = LayoutInflater.from(context);
}
...
@NonNull
@Override
public View getView(int position, View convertView, @NonNull ViewGroup parent) {
final MyViewHolder holder;
if (convertView == null) {
holder = MyViewHolder.create(inflater, parent);
convertView = holder.view;
convertView.setTag(holder);
} else {
holder = (MyViewHolder) convertView.getTag();
}
final MyData data = getItem(position);
assert data != null;
holder.bind(data);
return convertView;
}
}
Kotlin
class MyAdapter(context: Context, objects: List<MyData>) : ArrayAdapter<MyData>(context, 0, objects) {
private val inflater = LayoutInflater.from(context)
...
override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {
val view: View = convertView ?: MyViewHolder.create(inflater, parent)
.also { it.view.tag = it }
.view
getItem(position)?.let {
(view.tag as MyViewHolder).bind(it)
}
return view
}
}
2017年8月3日木曜日
Kotlin メモ : joinToString
kotlin-stdlib / kotlin.collections / joinToString
Java
Java
/**
* 00 11 22 33 44 55 66 77
*/
@NonNull
public String expression(byte[] bytes) {
final StringBuilder sb = new StringBuilder();
boolean firstTime = true;
for (byte each : bytes) {
if (firstTime) {
firstTime = false;
} else {
sb.append(" ");
}
sb.append(hex(each));
}
return sb.toString();
}
Java その2
/**
* 00 11 22 33 44 55 66 77
*/
@NonNull
public String expression(byte[] bytes) {
final List<String> tokens = new ArrayList<>();
for (byte each : bytes) {
tokens.add(hex(each));
}
return TextUtils.join(" ", tokens);
}
Kotlin
/**
* 00 11 22 33 44 55 66 77
*/
fun expression(bytes : ByteArray): String {
return bytes.joinToString(separator = " ", transform = { hex(it) })
}
2017年8月1日火曜日
Kotlin メモ : takeIf
Java
public Hoge createFromParcel(Parcel source) {
final int length = source.readInt();
final byte[] data;
if (length > 0) {
data = new byte[length];
source.readByteArray(data);
} else {
data = null;
}
return new Hoge(data);
}
Kotlin 変換直後
override fun createFromParcel(source: Parcel): Hoge {
val length = source.readInt()
val data: ByteArray?
if (length > 0) {
data = ByteArray(length)
source.readByteArray(data)
} else {
data = null
}
return Hoge(data)
}
source.run {} を使う
override fun createFromParcel(source: Parcel): Hoge = source.run {
val length = readInt()
val data: ByteArray?
if (length > 0) {
data = ByteArray(length)
readByteArray(data)
} else {
data = null
}
Hoge(data)
}
also を使う
override fun createFromParcel(source: Parcel): Hoge = source.run {
val length = readInt()
val data: ByteArray?
if (length > 0) {
data = ByteArray(length).also { readByteArray(it) }
} else {
data = null
}
Hoge(data)
}
if 式にしてみる
override fun createFromParcel(source: Parcel): Hoge = source.run {
val length = readInt()
val data: ByteArray? = if (length > 0) {
ByteArray(length).also { readByteArray(it) }
} else {
null
}
Hoge(data)
}
length に let を使う
override fun createFromParcel(source: Parcel): Hoge = source.run {
val length = readInt()
val data: ByteArray? = if (length > 0) {
length.let { ByteArray(it).also { readByteArray(it) } }
} else {
null
}
Hoge(data)
}
readInt() に takeIf を使う
override fun createFromParcel(source: Parcel): Hoge = source.run {
val data: ByteArray? = readInt()
.takeIf { it > 0 }
?.let { ByteArray(it).also { readByteArray(it) } }
Hoge(data)
}