Coding

newInstance in Java

Introduction

newInstance is used to instantiate an instance of a class dynamically. Here is an example written in Scala.

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class Printer() {
  def print(): Unit = {
    println(s"print something")
  }
}
object ScalaTest {
  def main(args: Array[String]): Unit = {
    val testClass = Class.forName("Printer").newInstance().asInstanceOf[Printer]
    testClass.print()
  }
}

Output

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print something

By the way, asInstanceOf[Printer] is used for casting in Scala, it’s just like (Printer) Class.forName("Printer").newInstance() in Java.

What if we want to call Printer’s constructor with arguments? We can use getDeclaredConstructor

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class Printer(val name: String, val description: String) {
  def print(): Unit = {
    println(s"product name: $name, description: $description")
  }
}
object ScalaTest {
  def main(args: Array[String]): Unit = {
    val testClass = Class.forName("Printer")
      .getDeclaredConstructor(classOf[String], classOf[String])
      .newInstance("kindle", "used for reading")
      .asInstanceOf[Printer]
    testClass.print()
  }
}

Output

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product name: kindle, description: used for reading
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