null을 다루는 방법

Java -> Kotlin

  public boolean startsWithA1(String str) {
    if (str == null) {
      throw new IllegalArgumentException("null이 들어왔습니다");
    }
    return str.startsWith("A");
  }

 fun startsWith(str: String?) : Boolean {
    return str?.startsWith("A")
        ?: throw java.lang.IllegalArgumentException("null이 들어왔습니다.")
}

Java -> Kotlin

  public Boolean startsWithA2(String str) {
    if (str == null) {
      return null;
    }
    return str.startsWith("A");
  }

fun startsWithA2(str: String?) : Boolean? {
    return str?.startsWith("A")
}

Java -> Kotlin

public boolean startsWithA3(String str) {
    if (str == null) {
      return false;
    }
    return str.startsWith("A");
  }

fun startsWithA3(str: String?): Boolean {
    return str?.startsWith("A") ?: false
}