I asked a Java developer why he has not tried Kotlin, there are not good resources for Java-to-Kotlin, he answered, So here is the Key Points to Compare !!
Some points to note: 1. Whatever you do in Kotlin can also be done in Java. 2. From language basics perspective, Kotlin is syntactical sugar over Java. I say Java is compiled, Kotlin is smartly compiled. 3. There are some cases where Kotlin is more efficient. 4. Kotlin will reduce your Code but not every time.