Kotlin Vs Java : What's The Best Choice for Mobile App Development?

public class JavaCode {
	public String toJSON(Collection<Integer> collection) {
    	StringBuilder sb = new StringBuilder();
    	sb.append("[");
    	Iterator<Integer> iterator = collection.iterator();
    	while (iterator.hasNext()) {
        	Integer element = iterator.next();
        	sb.append(element);
        	if (iterator.hasNext()) {
            	sb.append(", ");
        	}
    	}
    	sb.append("]");
    	return sb.toString();
	}
}

fun toJSON(collection: Collection<Int>): String {
	val sb = StringBuilder()
	sb.append("[")
	val iterator = collection.iterator()
	while (iterator.hasNext())
	{
    	val element = iterator.next()
    	sb.append(element)
    	if (iterator.hasNext())
    	{
        	sb.append(", ")
    	}
	}
	sb.append("]")
	return sb.toString()
}

StringBuilder sb = new StringBuilder();

val sb = StringBuilder()

val positives = list.filter { x -> x > 0 }

val positives = list.filter { it > 0 }

for ((k, v) in map) { println(“$k -> $v”) }

var a: String = "ABC"
a = null // compilation error

var b: String? ="abc"
b = null // ok

val listWithNulls: List<String?> = listOf("Kotlin Language", null)
for (item in listWithNulls Value) {
	item?.let { println(it) } // else prints A and ignores null
}

val l = b?.length ?: -1
is the equivalent of
val l: Int = if (b != null) b.length else -1

Appendable append(CharSequence cs) throws IOException;

try {
  log.append(message)
}
catch (IOException e) {
  // Do something with the exception
}