Question

I am new to scala.

here is simple code

---

object SimpleIfStatementDemo {
  def main(args: Array[String]) {   
    var numA: Int = args(0).toInt
    var numB: Int = args(1).toInt
    if(numA>numB) {
      print(numA)
    } else {
      print(numB)               
    }
  }
}

---

it’s can be compile,but can not be run it. here is error i got it

---

java.lang.ArrayIndexOutOfBoundsException: 0   at

Main$.main(SimpleIfSatementDemo.scala:5) at
Main.main(SimpleIfSatementDemo.scala) at
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597) at
scala.tools.nsc.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:78)
at
scala.tools.nsc.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:24)
at
scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:88)
at
scala.tools.nsc.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:78)
at
scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:33) at
scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:40) at
scala.tools.nsc.ScriptRunner.scala$tools$nsc$ScriptRunner$$runCompiled(ScriptRunner.scala:171)
at
scala.tools.nsc.ScriptRunner$$anonfun$runScript$1.apply(ScriptRunner.scala:188)
at
scala.tools.nsc.ScriptRunner$$anonfun$runScript$1.apply(ScriptRunner.scala:188)
at
scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply$mcZ$sp(ScriptRunner.scala:157)
at
scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply(ScriptRunner.scala:131)
at
scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply(ScriptRunner.scala:131)
at scala.tools.nsc.util.package$.waitingForThreads(package.scala:26)
at
scala.tools.nsc.ScriptRunner.withCompiledScript(ScriptRunner.scala:130)
at scala.tools.nsc.ScriptRunner.runScript(ScriptRunner.scala:188) at
scala.tools.nsc.ScriptRunner.runScriptAndCatch(ScriptRunner.scala:201)
at
scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:58)
at
scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:80)
at
scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:89)
at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

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Thanks

Answer 1

The program is not being passed enough arguments (it requires at least two; see the java command manual for how these can be specified). Consider putting this code as the first line of the main method:

println("I have " + args.length + " argument(s)")

And then try this on the Scala REPL to see a similar explosion:

val a = Array("Hello world!") // array of one element
a(0)      // access first element, okay
a(1)      // access second element -- KABOOM!

How can this new knowledge be used to make the program more robust (and not throw the exception)?

Happy coding.

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The article First Steps to Scala has examples of passing and using arguments.